From 6bf0a5cb5034a7e684dcc3500e841785237ce2dd Mon Sep 17 00:00:00 2001
From: Daniel Baumann <daniel.baumann@progress-linux.org>
Date: Sun, 7 Apr 2024 19:32:43 +0200
Subject: Adding upstream version 1:115.7.0.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
---
 editor/libeditor/HTMLEditorDeleteHandler.cpp | 6854 ++++++++++++++++++++++++++
 1 file changed, 6854 insertions(+)
 create mode 100644 editor/libeditor/HTMLEditorDeleteHandler.cpp

(limited to 'editor/libeditor/HTMLEditorDeleteHandler.cpp')

diff --git a/editor/libeditor/HTMLEditorDeleteHandler.cpp b/editor/libeditor/HTMLEditorDeleteHandler.cpp
new file mode 100644
index 0000000000..928d9b3b4c
--- /dev/null
+++ b/editor/libeditor/HTMLEditorDeleteHandler.cpp
@@ -0,0 +1,6854 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=2 sw=2 et tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "HTMLEditor.h"
+#include "HTMLEditorNestedClasses.h"
+
+#include <algorithm>
+#include <utility>
+
+#include "AutoRangeArray.h"
+#include "CSSEditUtils.h"
+#include "EditAction.h"
+#include "EditorDOMPoint.h"
+#include "EditorUtils.h"
+#include "HTMLEditHelpers.h"
+#include "HTMLEditUtils.h"
+#include "WSRunObject.h"
+
+#include "ErrorList.h"
+#include "js/ErrorReport.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/CheckedInt.h"
+#include "mozilla/ComputedStyle.h"  // for ComputedStyle
+#include "mozilla/ContentIterator.h"
+#include "mozilla/EditorDOMPoint.h"
+#include "mozilla/EditorForwards.h"
+#include "mozilla/InternalMutationEvent.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/OwningNonNull.h"
+#include "mozilla/SelectionState.h"
+#include "mozilla/StaticPrefs_editor.h"  // for StaticPrefs::editor_*
+#include "mozilla/Unused.h"
+#include "mozilla/dom/AncestorIterator.h"
+#include "mozilla/dom/Element.h"
+#include "mozilla/dom/HTMLBRElement.h"
+#include "mozilla/dom/Selection.h"
+#include "mozilla/mozalloc.h"
+#include "nsAString.h"
+#include "nsAtom.h"
+#include "nsComputedDOMStyle.h"  // for nsComputedDOMStyle
+#include "nsContentUtils.h"
+#include "nsDebug.h"
+#include "nsError.h"
+#include "nsFrameSelection.h"
+#include "nsGkAtoms.h"
+#include "nsIContent.h"
+#include "nsINode.h"
+#include "nsRange.h"
+#include "nsString.h"
+#include "nsStringFwd.h"
+#include "nsStyleConsts.h"  // for StyleWhiteSpace
+#include "nsTArray.h"
+
+// NOTE: This file was split from:
+//   https://searchfox.org/mozilla-central/rev/c409dd9235c133ab41eba635f906aa16e050c197/editor/libeditor/HTMLEditSubActionHandler.cpp
+
+namespace mozilla {
+
+using namespace dom;
+using EmptyCheckOption = HTMLEditUtils::EmptyCheckOption;
+using InvisibleWhiteSpaces = HTMLEditUtils::InvisibleWhiteSpaces;
+using LeafNodeType = HTMLEditUtils::LeafNodeType;
+using ScanLineBreak = HTMLEditUtils::ScanLineBreak;
+using TableBoundary = HTMLEditUtils::TableBoundary;
+using WalkTreeOption = HTMLEditUtils::WalkTreeOption;
+
+template Result<CaretPoint, nsresult>
+HTMLEditor::DeleteTextAndTextNodesWithTransaction(
+    const EditorDOMPoint& aStartPoint, const EditorDOMPoint& aEndPoint,
+    TreatEmptyTextNodes aTreatEmptyTextNodes);
+template Result<CaretPoint, nsresult>
+HTMLEditor::DeleteTextAndTextNodesWithTransaction(
+    const EditorDOMPointInText& aStartPoint,
+    const EditorDOMPointInText& aEndPoint,
+    TreatEmptyTextNodes aTreatEmptyTextNodes);
+
+/*****************************************************************************
+ * AutoSetTemporaryAncestorLimiter
+ ****************************************************************************/
+
+class MOZ_RAII AutoSetTemporaryAncestorLimiter final {
+ public:
+  AutoSetTemporaryAncestorLimiter(const HTMLEditor& aHTMLEditor,
+                                  Selection& aSelection,
+                                  nsINode& aStartPointNode,
+                                  AutoRangeArray* aRanges = nullptr) {
+    MOZ_ASSERT(aSelection.GetType() == SelectionType::eNormal);
+
+    if (aSelection.GetAncestorLimiter()) {
+      return;
+    }
+
+    Element* selectionRootElement =
+        aHTMLEditor.FindSelectionRoot(aStartPointNode);
+    if (!selectionRootElement) {
+      return;
+    }
+    aHTMLEditor.InitializeSelectionAncestorLimit(*selectionRootElement);
+    mSelection = &aSelection;
+    // Setting ancestor limiter may change ranges which were outer of
+    // the new limiter.  Therefore, we need to reinitialize aRanges.
+    if (aRanges) {
+      aRanges->Initialize(aSelection);
+    }
+  }
+
+  ~AutoSetTemporaryAncestorLimiter() {
+    if (mSelection) {
+      mSelection->SetAncestorLimiter(nullptr);
+    }
+  }
+
+ private:
+  RefPtr<Selection> mSelection;
+};
+
+/*****************************************************************************
+ * AutoDeleteRangesHandler
+ ****************************************************************************/
+
+class MOZ_STACK_CLASS HTMLEditor::AutoDeleteRangesHandler final {
+ public:
+  explicit AutoDeleteRangesHandler(
+      const AutoDeleteRangesHandler* aParent = nullptr)
+      : mParent(aParent),
+        mOriginalDirectionAndAmount(nsIEditor::eNone),
+        mOriginalStripWrappers(nsIEditor::eNoStrip) {}
+
+  /**
+   * ComputeRangesToDelete() computes actual deletion ranges.
+   */
+  [[nodiscard]] MOZ_CAN_RUN_SCRIPT nsresult ComputeRangesToDelete(
+      const HTMLEditor& aHTMLEditor, nsIEditor::EDirection aDirectionAndAmount,
+      AutoRangeArray& aRangesToDelete, const Element& aEditingHost);
+
+  /**
+   * Deletes content in or around aRangesToDelete.
+   * NOTE: This method creates SelectionBatcher.  Therefore, each caller
+   *       needs to check if the editor is still available even if this returns
+   *       NS_OK.
+   */
+  [[nodiscard]] MOZ_CAN_RUN_SCRIPT Result<EditActionResult, nsresult> Run(
+      HTMLEditor& aHTMLEditor, nsIEditor::EDirection aDirectionAndAmount,
+      nsIEditor::EStripWrappers aStripWrappers, AutoRangeArray& aRangesToDelete,
+      const Element& aEditingHost);
+
+ private:
+  bool IsHandlingRecursively() const { return mParent != nullptr; }
+
+  bool CanFallbackToDeleteRangesWithTransaction(
+      const AutoRangeArray& aRangesToDelete) const {
+    return !IsHandlingRecursively() && !aRangesToDelete.Ranges().IsEmpty() &&
+           (!aRangesToDelete.IsCollapsed() ||
+            EditorBase::HowToHandleCollapsedRangeFor(
+                mOriginalDirectionAndAmount) !=
+                EditorBase::HowToHandleCollapsedRange::Ignore);
+  }
+
+  /**
+   * HandleDeleteAroundCollapsedRanges() handles deletion with collapsed
+   * ranges.  Callers must guarantee that this is called only when
+   * aRangesToDelete.IsCollapsed() returns true.
+   *
+   * @param aDirectionAndAmount Direction of the deletion.
+   * @param aStripWrappers      Must be eStrip or eNoStrip.
+   * @param aRangesToDelete     Ranges to delete.  This `IsCollapsed()` must
+   *                            return true.
+   * @param aWSRunScannerAtCaret        Scanner instance which scanned from
+   *                                    caret point.
+   * @param aScanFromCaretPointResult   Scan result of aWSRunScannerAtCaret
+   *                                    toward aDirectionAndAmount.
+   * @param aEditingHost        The editing host.
+   */
+  [[nodiscard]] MOZ_CAN_RUN_SCRIPT Result<EditActionResult, nsresult>
+  HandleDeleteAroundCollapsedRanges(
+      HTMLEditor& aHTMLEditor, nsIEditor::EDirection aDirectionAndAmount,
+      nsIEditor::EStripWrappers aStripWrappers, AutoRangeArray& aRangesToDelete,
+      const WSRunScanner& aWSRunScannerAtCaret,
+      const WSScanResult& aScanFromCaretPointResult,
+      const Element& aEditingHost);
+  nsresult ComputeRangesToDeleteAroundCollapsedRanges(
+      const HTMLEditor& aHTMLEditor, nsIEditor::EDirection aDirectionAndAmount,
+      AutoRangeArray& aRangesToDelete, const WSRunScanner& aWSRunScannerAtCaret,
+      const WSScanResult& aScanFromCaretPointResult,
+      const Element& aEditingHost) const;
+
+  /**
+   * HandleDeleteNonCollapsedRanges() handles deletion with non-collapsed
+   * ranges.  Callers must guarantee that this is called only when
+   * aRangesToDelete.IsCollapsed() returns false.
+   *
+   * @param aDirectionAndAmount         Direction of the deletion.
+   * @param aStripWrappers              Must be eStrip or eNoStrip.
+   * @param aRangesToDelete             The ranges to delete.
+   * @param aSelectionWasCollapsed      If the caller extended `Selection`
+   *                                    from collapsed, set this to `Yes`.
+   *                                    Otherwise, i.e., `Selection` is not
+   *                                    collapsed from the beginning, set
+   *                                    this to `No`.
+   * @param aEditingHost                The editing host.
+   */
+  enum class SelectionWasCollapsed { Yes, No };
+  [[nodiscard]] MOZ_CAN_RUN_SCRIPT Result<EditActionResult, nsresult>
+  HandleDeleteNonCollapsedRanges(HTMLEditor& aHTMLEditor,
+                                 nsIEditor::EDirection aDirectionAndAmount,
+                                 nsIEditor::EStripWrappers aStripWrappers,
+                                 AutoRangeArray& aRangesToDelete,
+                                 SelectionWasCollapsed aSelectionWasCollapsed,
+                                 const Element& aEditingHost);
+  nsresult ComputeRangesToDeleteNonCollapsedRanges(
+      const HTMLEditor& aHTMLEditor, nsIEditor::EDirection aDirectionAndAmount,
+      AutoRangeArray& aRangesToDelete,
+      SelectionWasCollapsed aSelectionWasCollapsed,
+      const Element& aEditingHost) const;
+
+  /**
+   * Handle deletion of collapsed ranges in a text node.
+   *
+   * @param aDirectionAndAmount Must be eNext or ePrevious.
+   * @param aCaretPosition      The position where caret is.  This container
+   *                            must be a text node.
+   * @param aEditingHost        The editing host.
+   */
+  [[nodiscard]] MOZ_CAN_RUN_SCRIPT Result<CaretPoint, nsresult>
+  HandleDeleteTextAroundCollapsedRanges(
+      HTMLEditor& aHTMLEditor, nsIEditor::EDirection aDirectionAndAmount,
+      AutoRangeArray& aRangesToDelete, const Element& aEditingHost);
+  nsresult ComputeRangesToDeleteTextAroundCollapsedRanges(
+      nsIEditor::EDirection aDirectionAndAmount,
+      AutoRangeArray& aRangesToDelete, const Element& aEditingHost) const;
+
+  /**
+   * Handles deletion of collapsed selection at white-spaces in a text node.
+   *
+   * @param aDirectionAndAmount Direction of the deletion.
+   * @param aPointToDelete      The point to delete.  I.e., typically, caret
+   *                            position.
+   * @param aEditingHost        The editing host.
+   */
+  [[nodiscard]] MOZ_CAN_RUN_SCRIPT Result<CaretPoint, nsresult>
+  HandleDeleteCollapsedSelectionAtWhiteSpaces(
+      HTMLEditor& aHTMLEditor, nsIEditor::EDirection aDirectionAndAmount,
+      const EditorDOMPoint& aPointToDelete, const Element& aEditingHost);
+
+  /**
+   * Handle deletion of collapsed selection in a text node.
+   *
+   * @param aDirectionAndAmount Direction of the deletion.
+   * @param aRangesToDelete     Computed selection ranges to delete.
+   * @param aPointAtDeletingChar   The visible char position which you want to
+   *                               delete.
+   * @param aEditingHost        The editing host.
+   */
+  [[nodiscard]] MOZ_CAN_RUN_SCRIPT Result<CaretPoint, nsresult>
+  HandleDeleteCollapsedSelectionAtVisibleChar(
+      HTMLEditor& aHTMLEditor, nsIEditor::EDirection aDirectionAndAmount,
+      AutoRangeArray& aRangesToDelete,
+      const EditorDOMPoint& aPointAtDeletingChar, const Element& aEditingHost);
+
+  /**
+   * Handle deletion of atomic elements like <br>, <hr>, <img>, <input>, etc and
+   * data nodes except text node (e.g., comment node). Note that don't call this
+   * directly with `<hr>` element.
+   *
+   * @param aAtomicContent      The atomic content to be deleted.
+   * @param aCaretPoint         The caret point (i.e., selection start or
+   *                            end).
+   * @param aWSRunScannerAtCaret WSRunScanner instance which was initialized
+   *                             with the caret point.
+   * @param aEditingHost        The editing host.
+   */
+  [[nodiscard]] MOZ_CAN_RUN_SCRIPT Result<CaretPoint, nsresult>
+  HandleDeleteAtomicContent(HTMLEditor& aHTMLEditor, nsIContent& aAtomicContent,
+                            const EditorDOMPoint& aCaretPoint,
+                            const WSRunScanner& aWSRunScannerAtCaret,
+                            const Element& aEditingHost);
+  nsresult ComputeRangesToDeleteAtomicContent(
+      Element* aEditingHost, const nsIContent& aAtomicContent,
+      AutoRangeArray& aRangesToDelete) const;
+
+  /**
+   * GetAtomicContnetToDelete() returns better content that is deletion of
+   * atomic element.  If aScanFromCaretPointResult is special, since this
+   * point may not be editable, we look for better point to remove atomic
+   * content.
+   *
+   * @param aDirectionAndAmount       Direction of the deletion.
+   * @param aWSRunScannerAtCaret      WSRunScanner instance which was
+   *                                  initialized with the caret point.
+   * @param aScanFromCaretPointResult Scan result of aWSRunScannerAtCaret
+   *                                  toward aDirectionAndAmount.
+   */
+  static nsIContent* GetAtomicContentToDelete(
+      nsIEditor::EDirection aDirectionAndAmount,
+      const WSRunScanner& aWSRunScannerAtCaret,
+      const WSScanResult& aScanFromCaretPointResult) MOZ_NONNULL_RETURN;
+
+  /**
+   * HandleDeleteAtOtherBlockBoundary() handles deletion at other block boundary
+   * (i.e., immediately before or after a block). If this does not join blocks,
+   * `Run()` may be called recursively with creating another instance.
+   *
+   * @param aDirectionAndAmount Direction of the deletion.
+   * @param aStripWrappers      Must be eStrip or eNoStrip.
+   * @param aOtherBlockElement  The block element which follows the caret or
+   *                            is followed by caret.
+   * @param aCaretPoint         The caret point (i.e., selection start or
+   *                            end).
+   * @param aWSRunScannerAtCaret WSRunScanner instance which was initialized
+   *                             with the caret point.
+   * @param aRangesToDelete     Ranges to delete of the caller.  This should
+   *                            be collapsed and the point should match with
+   *                            aCaretPoint.
+   * @param aEditingHost        The editing host.
+   */
+  [[nodiscard]] MOZ_CAN_RUN_SCRIPT Result<EditActionResult, nsresult>
+  HandleDeleteAtOtherBlockBoundary(
+      HTMLEditor& aHTMLEditor, nsIEditor::EDirection aDirectionAndAmount,
+      nsIEditor::EStripWrappers aStripWrappers, Element& aOtherBlockElement,
+      const EditorDOMPoint& aCaretPoint, WSRunScanner& aWSRunScannerAtCaret,
+      AutoRangeArray& aRangesToDelete, const Element& aEditingHost);
+
+  /**
+   * ExtendOrShrinkRangeToDelete() extends aRangeToDelete if there are
+   * an invisible <br> element and/or some parent empty elements.
+   *
+   * @param aFrameSelection     If the caller wants range in selection limiter,
+   *                            set this to non-nullptr which knows the limiter.
+   * @param aRangeToDelete       The range to be extended for deletion.  This
+   *                            must not be collapsed, must be positioned.
+   */
+  template <typename EditorDOMRangeType>
+  Result<EditorRawDOMRange, nsresult> ExtendOrShrinkRangeToDelete(
+      const HTMLEditor& aHTMLEditor, const nsFrameSelection* aFrameSelection,
+      const EditorDOMRangeType& aRangeToDelete) const;
+
+  /**
+   * A helper method for ExtendOrShrinkRangeToDelete().  This returns shrunken
+   * range if aRangeToDelete selects all over list elements which have some list
+   * item elements to avoid to delete all list items from the list element.
+   */
+  MOZ_NEVER_INLINE_DEBUG static EditorRawDOMRange
+  GetRangeToAvoidDeletingAllListItemsIfSelectingAllOverListElements(
+      const EditorRawDOMRange& aRangeToDelete);
+
+  /**
+   * DeleteUnnecessaryNodes() removes unnecessary nodes around aRange.
+   * Note that aRange is tracked with AutoTrackDOMRange.
+   */
+  [[nodiscard]] MOZ_CAN_RUN_SCRIPT nsresult
+  DeleteUnnecessaryNodes(HTMLEditor& aHTMLEditor, EditorDOMRange& aRange);
+
+  /**
+   * DeleteUnnecessaryNodesAndCollapseSelection() calls DeleteUnnecessaryNodes()
+   * and then, collapse selection at tracked aSelectionStartPoint or
+   * aSelectionEndPoint (depending on aDirectionAndAmount).
+   *
+   * @param aDirectionAndAmount         Direction of the deletion.
+   *                                    If nsIEditor::ePrevious, selection
+   *                                    will be collapsed to aSelectionEndPoint.
+   *                                    Otherwise, selection will be collapsed
+   *                                    to aSelectionStartPoint.
+   * @param aSelectionStartPoint        First selection range start after
+   *                                    computing the deleting range.
+   * @param aSelectionEndPoint          First selection range end after
+   *                                    computing the deleting range.
+   */
+  [[nodiscard]] MOZ_CAN_RUN_SCRIPT nsresult
+  DeleteUnnecessaryNodesAndCollapseSelection(
+      HTMLEditor& aHTMLEditor, nsIEditor::EDirection aDirectionAndAmount,
+      const EditorDOMPoint& aSelectionStartPoint,
+      const EditorDOMPoint& aSelectionEndPoint);
+
+  /**
+   * If aContent is a text node that contains only collapsed white-space or
+   * empty and editable.
+   */
+  [[nodiscard]] MOZ_CAN_RUN_SCRIPT nsresult
+  DeleteNodeIfInvisibleAndEditableTextNode(HTMLEditor& aHTMLEditor,
+                                           nsIContent& aContent);
+
+  /**
+   * DeleteParentBlocksIfEmpty() removes parent block elements if they
+   * don't have visible contents.  Note that due performance issue of
+   * WhiteSpaceVisibilityKeeper, this call may be expensive.  And also note that
+   * this removes a empty block with a transaction.  So, please make sure that
+   * you've already created `AutoPlaceholderBatch`.
+   *
+   * @param aPoint      The point whether this method climbing up the DOM
+   *                    tree to remove empty parent blocks.
+   * @return            NS_OK if one or more empty block parents are deleted.
+   *                    NS_SUCCESS_EDITOR_ELEMENT_NOT_FOUND if the point is
+   *                    not in empty block.
+   *                    Or NS_ERROR_* if something unexpected occurs.
+   */
+  [[nodiscard]] MOZ_CAN_RUN_SCRIPT nsresult
+  DeleteParentBlocksWithTransactionIfEmpty(HTMLEditor& aHTMLEditor,
+                                           const EditorDOMPoint& aPoint);
+
+  [[nodiscard]] MOZ_CAN_RUN_SCRIPT Result<CaretPoint, nsresult>
+  FallbackToDeleteRangesWithTransaction(HTMLEditor& aHTMLEditor,
+                                        AutoRangeArray& aRangesToDelete) const {
+    MOZ_ASSERT(aHTMLEditor.IsEditActionDataAvailable());
+    MOZ_ASSERT(CanFallbackToDeleteRangesWithTransaction(aRangesToDelete));
+    Result<CaretPoint, nsresult> caretPointOrError =
+        aHTMLEditor.DeleteRangesWithTransaction(mOriginalDirectionAndAmount,
+                                                mOriginalStripWrappers,
+                                                aRangesToDelete);
+    NS_WARNING_ASSERTION(caretPointOrError.isOk(),
+                         "HTMLEditor::DeleteRangesWithTransaction() failed");
+    return caretPointOrError;
+  }
+
+  /**
+   * ComputeRangesToDeleteRangesWithTransaction() computes target ranges
+   * which will be called by `EditorBase::DeleteRangesWithTransaction()`.
+   * TODO: We should not use it for consistency with each deletion handler
+   *       in this and nested classes.
+   */
+  nsresult ComputeRangesToDeleteRangesWithTransaction(
+      const HTMLEditor& aHTMLEditor, nsIEditor::EDirection aDirectionAndAmount,
+      AutoRangeArray& aRangesToDelete) const;
+
+  nsresult FallbackToComputeRangesToDeleteRangesWithTransaction(
+      const HTMLEditor& aHTMLEditor, AutoRangeArray& aRangesToDelete) const {
+    MOZ_ASSERT(aHTMLEditor.IsEditActionDataAvailable());
+    MOZ_ASSERT(CanFallbackToDeleteRangesWithTransaction(aRangesToDelete));
+    nsresult rv = ComputeRangesToDeleteRangesWithTransaction(
+        aHTMLEditor, mOriginalDirectionAndAmount, aRangesToDelete);
+    NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                         "AutoDeleteRangesHandler::"
+                         "ComputeRangesToDeleteRangesWithTransaction() failed");
+    return rv;
+  }
+
+  class MOZ_STACK_CLASS AutoBlockElementsJoiner final {
+   public:
+    AutoBlockElementsJoiner() = delete;
+    explicit AutoBlockElementsJoiner(
+        AutoDeleteRangesHandler& aDeleteRangesHandler)
+        : mDeleteRangesHandler(&aDeleteRangesHandler),
+          mDeleteRangesHandlerConst(aDeleteRangesHandler) {}
+    explicit AutoBlockElementsJoiner(
+        const AutoDeleteRangesHandler& aDeleteRangesHandler)
+        : mDeleteRangesHandler(nullptr),
+          mDeleteRangesHandlerConst(aDeleteRangesHandler) {}
+
+    /**
+     * PrepareToDeleteAtCurrentBlockBoundary() considers left content and right
+     * content which are joined for handling deletion at current block boundary
+     * (i.e., at start or end of the current block).
+     *
+     * @param aHTMLEditor               The HTML editor.
+     * @param aDirectionAndAmount       Direction of the deletion.
+     * @param aCurrentBlockElement      The current block element.
+     * @param aCaretPoint               The caret point (i.e., selection start
+     *                                  or end).
+     * @return                          true if can continue to handle the
+     *                                  deletion.
+     */
+    bool PrepareToDeleteAtCurrentBlockBoundary(
+        const HTMLEditor& aHTMLEditor,
+        nsIEditor::EDirection aDirectionAndAmount,
+        Element& aCurrentBlockElement, const EditorDOMPoint& aCaretPoint);
+
+    /**
+     * PrepareToDeleteAtOtherBlockBoundary() considers left content and right
+     * content which are joined for handling deletion at other block boundary
+     * (i.e., immediately before or after a block).
+     *
+     * @param aHTMLEditor               The HTML editor.
+     * @param aDirectionAndAmount       Direction of the deletion.
+     * @param aOtherBlockElement        The block element which follows the
+     *                                  caret or is followed by caret.
+     * @param aCaretPoint               The caret point (i.e., selection start
+     *                                  or end).
+     * @param aWSRunScannerAtCaret      WSRunScanner instance which was
+     *                                  initialized with the caret point.
+     * @return                          true if can continue to handle the
+     *                                  deletion.
+     */
+    bool PrepareToDeleteAtOtherBlockBoundary(
+        const HTMLEditor& aHTMLEditor,
+        nsIEditor::EDirection aDirectionAndAmount, Element& aOtherBlockElement,
+        const EditorDOMPoint& aCaretPoint,
+        const WSRunScanner& aWSRunScannerAtCaret);
+
+    /**
+     * PrepareToDeleteNonCollapsedRanges() considers left block element and
+     * right block element which are inclusive ancestor block element of
+     * start and end container of first range of aRangesToDelete.
+     *
+     * @param aHTMLEditor               The HTML editor.
+     * @param aRangesToDelete           Ranges to delete.  Must not be
+     *                                  collapsed.
+     * @return                          true if can continue to handle the
+     *                                  deletion.
+     */
+    bool PrepareToDeleteNonCollapsedRanges(
+        const HTMLEditor& aHTMLEditor, const AutoRangeArray& aRangesToDelete);
+
+    /**
+     * Run() executes the joining.
+     *
+     * @param aHTMLEditor               The HTML editor.
+     * @param aDirectionAndAmount       Direction of the deletion.
+     * @param aStripWrappers            Must be eStrip or eNoStrip.
+     * @param aCaretPoint               The caret point (i.e., selection start
+     *                                  or end).
+     * @param aRangesToDelete           Ranges to delete of the caller.
+     *                                  This should be collapsed and match
+     *                                  with aCaretPoint.
+     */
+    [[nodiscard]] MOZ_CAN_RUN_SCRIPT Result<EditActionResult, nsresult> Run(
+        HTMLEditor& aHTMLEditor, nsIEditor::EDirection aDirectionAndAmount,
+        nsIEditor::EStripWrappers aStripWrappers,
+        const EditorDOMPoint& aCaretPoint, AutoRangeArray& aRangesToDelete,
+        const Element& aEditingHost) {
+      switch (mMode) {
+        case Mode::JoinCurrentBlock: {
+          Result<EditActionResult, nsresult> result =
+              HandleDeleteAtCurrentBlockBoundary(
+                  aHTMLEditor, aDirectionAndAmount, aCaretPoint, aEditingHost);
+          NS_WARNING_ASSERTION(result.isOk(),
+                               "AutoBlockElementsJoiner::"
+                               "HandleDeleteAtCurrentBlockBoundary() failed");
+          return result;
+        }
+        case Mode::JoinOtherBlock: {
+          Result<EditActionResult, nsresult> result =
+              HandleDeleteAtOtherBlockBoundary(aHTMLEditor, aDirectionAndAmount,
+                                               aStripWrappers, aCaretPoint,
+                                               aRangesToDelete, aEditingHost);
+          NS_WARNING_ASSERTION(result.isOk(),
+                               "AutoBlockElementsJoiner::"
+                               "HandleDeleteAtOtherBlockBoundary() failed");
+          return result;
+        }
+        case Mode::DeleteBRElement: {
+          Result<EditActionResult, nsresult> result =
+              DeleteBRElement(aHTMLEditor, aDirectionAndAmount, aEditingHost);
+          NS_WARNING_ASSERTION(
+              result.isOk(),
+              "AutoBlockElementsJoiner::DeleteBRElement() failed");
+          return result;
+        }
+        case Mode::JoinBlocksInSameParent:
+        case Mode::DeleteContentInRanges:
+        case Mode::DeleteNonCollapsedRanges:
+          MOZ_ASSERT_UNREACHABLE(
+              "This mode should be handled in the other Run()");
+          return Err(NS_ERROR_UNEXPECTED);
+        case Mode::NotInitialized:
+          return EditActionResult::IgnoredResult();
+      }
+      return Err(NS_ERROR_NOT_INITIALIZED);
+    }
+
+    nsresult ComputeRangesToDelete(const HTMLEditor& aHTMLEditor,
+                                   nsIEditor::EDirection aDirectionAndAmount,
+                                   const EditorDOMPoint& aCaretPoint,
+                                   AutoRangeArray& aRangesToDelete,
+                                   const Element& aEditingHost) const {
+      switch (mMode) {
+        case Mode::JoinCurrentBlock: {
+          nsresult rv = ComputeRangesToDeleteAtCurrentBlockBoundary(
+              aHTMLEditor, aCaretPoint, aRangesToDelete, aEditingHost);
+          NS_WARNING_ASSERTION(
+              NS_SUCCEEDED(rv),
+              "AutoBlockElementsJoiner::"
+              "ComputeRangesToDeleteAtCurrentBlockBoundary() failed");
+          return rv;
+        }
+        case Mode::JoinOtherBlock: {
+          nsresult rv = ComputeRangesToDeleteAtOtherBlockBoundary(
+              aHTMLEditor, aDirectionAndAmount, aCaretPoint, aRangesToDelete,
+              aEditingHost);
+          NS_WARNING_ASSERTION(
+              NS_SUCCEEDED(rv),
+              "AutoBlockElementsJoiner::"
+              "ComputeRangesToDeleteAtOtherBlockBoundary() failed");
+          return rv;
+        }
+        case Mode::DeleteBRElement: {
+          nsresult rv = ComputeRangesToDeleteBRElement(aRangesToDelete);
+          NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                               "AutoBlockElementsJoiner::"
+                               "ComputeRangesToDeleteBRElement() failed");
+          return rv;
+        }
+        case Mode::JoinBlocksInSameParent:
+        case Mode::DeleteContentInRanges:
+        case Mode::DeleteNonCollapsedRanges:
+          MOZ_ASSERT_UNREACHABLE(
+              "This mode should be handled in the other "
+              "ComputeRangesToDelete()");
+          return NS_ERROR_UNEXPECTED;
+        case Mode::NotInitialized:
+          return NS_OK;
+      }
+      return NS_ERROR_NOT_IMPLEMENTED;
+    }
+
+    /**
+     * Run() executes the joining.
+     *
+     * @param aHTMLEditor               The HTML editor.
+     * @param aDirectionAndAmount       Direction of the deletion.
+     * @param aStripWrappers            Whether delete or keep new empty
+     *                                  ancestor elements.
+     * @param aRangesToDelete           Ranges to delete.  Must not be
+     *                                  collapsed.
+     * @param aSelectionWasCollapsed    Whether selection was or was not
+     *                                  collapsed when starting to handle
+     *                                  deletion.
+     */
+    [[nodiscard]] MOZ_CAN_RUN_SCRIPT Result<EditActionResult, nsresult> Run(
+        HTMLEditor& aHTMLEditor, nsIEditor::EDirection aDirectionAndAmount,
+        nsIEditor::EStripWrappers aStripWrappers,
+        AutoRangeArray& aRangesToDelete,
+        AutoDeleteRangesHandler::SelectionWasCollapsed aSelectionWasCollapsed,
+        const Element& aEditingHost) {
+      switch (mMode) {
+        case Mode::JoinCurrentBlock:
+        case Mode::JoinOtherBlock:
+        case Mode::DeleteBRElement:
+          MOZ_ASSERT_UNREACHABLE(
+              "This mode should be handled in the other Run()");
+          return Err(NS_ERROR_UNEXPECTED);
+        case Mode::JoinBlocksInSameParent: {
+          Result<EditActionResult, nsresult> result =
+              JoinBlockElementsInSameParent(
+                  aHTMLEditor, aDirectionAndAmount, aStripWrappers,
+                  aRangesToDelete, aSelectionWasCollapsed, aEditingHost);
+          NS_WARNING_ASSERTION(result.isOk(),
+                               "AutoBlockElementsJoiner::"
+                               "JoinBlockElementsInSameParent() failed");
+          return result;
+        }
+        case Mode::DeleteContentInRanges: {
+          Result<EditActionResult, nsresult> result =
+              DeleteContentInRanges(aHTMLEditor, aDirectionAndAmount,
+                                    aStripWrappers, aRangesToDelete);
+          NS_WARNING_ASSERTION(
+              result.isOk(),
+              "AutoBlockElementsJoiner::DeleteContentInRanges() failed");
+          return result;
+        }
+        case Mode::DeleteNonCollapsedRanges: {
+          Result<EditActionResult, nsresult> result =
+              HandleDeleteNonCollapsedRanges(
+                  aHTMLEditor, aDirectionAndAmount, aStripWrappers,
+                  aRangesToDelete, aSelectionWasCollapsed, aEditingHost);
+          NS_WARNING_ASSERTION(result.isOk(),
+                               "AutoBlockElementsJoiner::"
+                               "HandleDeleteNonCollapsedRange() failed");
+          return result;
+        }
+        case Mode::NotInitialized:
+          MOZ_ASSERT_UNREACHABLE(
+              "Call Run() after calling a preparation method");
+          return EditActionResult::IgnoredResult();
+      }
+      return Err(NS_ERROR_NOT_INITIALIZED);
+    }
+
+    nsresult ComputeRangesToDelete(
+        const HTMLEditor& aHTMLEditor,
+        nsIEditor::EDirection aDirectionAndAmount,
+        AutoRangeArray& aRangesToDelete,
+        AutoDeleteRangesHandler::SelectionWasCollapsed aSelectionWasCollapsed,
+        const Element& aEditingHost) const {
+      switch (mMode) {
+        case Mode::JoinCurrentBlock:
+        case Mode::JoinOtherBlock:
+        case Mode::DeleteBRElement:
+          MOZ_ASSERT_UNREACHABLE(
+              "This mode should be handled in the other "
+              "ComputeRangesToDelete()");
+          return NS_ERROR_UNEXPECTED;
+        case Mode::JoinBlocksInSameParent: {
+          nsresult rv = ComputeRangesToJoinBlockElementsInSameParent(
+              aHTMLEditor, aDirectionAndAmount, aRangesToDelete);
+          NS_WARNING_ASSERTION(
+              NS_SUCCEEDED(rv),
+              "AutoBlockElementsJoiner::"
+              "ComputeRangesToJoinBlockElementsInSameParent() failed");
+          return rv;
+        }
+        case Mode::DeleteContentInRanges: {
+          nsresult rv = ComputeRangesToDeleteContentInRanges(
+              aHTMLEditor, aDirectionAndAmount, aRangesToDelete);
+          NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                               "AutoBlockElementsJoiner::"
+                               "ComputeRangesToDeleteContentInRanges() failed");
+          return rv;
+        }
+        case Mode::DeleteNonCollapsedRanges: {
+          nsresult rv = ComputeRangesToDeleteNonCollapsedRanges(
+              aHTMLEditor, aDirectionAndAmount, aRangesToDelete,
+              aSelectionWasCollapsed, aEditingHost);
+          NS_WARNING_ASSERTION(
+              NS_SUCCEEDED(rv),
+              "AutoBlockElementsJoiner::"
+              "ComputeRangesToDeleteNonCollapsedRanges() failed");
+          return rv;
+        }
+        case Mode::NotInitialized:
+          MOZ_ASSERT_UNREACHABLE(
+              "Call ComputeRangesToDelete() after calling a preparation "
+              "method");
+          return NS_ERROR_NOT_INITIALIZED;
+      }
+      return NS_ERROR_NOT_INITIALIZED;
+    }
+
+    nsIContent* GetLeafContentInOtherBlockElement() const {
+      MOZ_ASSERT(mMode == Mode::JoinOtherBlock);
+      return mLeafContentInOtherBlock;
+    }
+
+   private:
+    [[nodiscard]] MOZ_CAN_RUN_SCRIPT Result<EditActionResult, nsresult>
+    HandleDeleteAtCurrentBlockBoundary(
+        HTMLEditor& aHTMLEditor, nsIEditor::EDirection aDirectionAndAmount,
+        const EditorDOMPoint& aCaretPoint, const Element& aEditingHost);
+    nsresult ComputeRangesToDeleteAtCurrentBlockBoundary(
+        const HTMLEditor& aHTMLEditor, const EditorDOMPoint& aCaretPoint,
+        AutoRangeArray& aRangesToDelete, const Element& aEditingHost) const;
+    [[nodiscard]] MOZ_CAN_RUN_SCRIPT Result<EditActionResult, nsresult>
+    HandleDeleteAtOtherBlockBoundary(HTMLEditor& aHTMLEditor,
+                                     nsIEditor::EDirection aDirectionAndAmount,
+                                     nsIEditor::EStripWrappers aStripWrappers,
+                                     const EditorDOMPoint& aCaretPoint,
+                                     AutoRangeArray& aRangesToDelete,
+                                     const Element& aEditingHost);
+    // FYI: This method may modify selection, but it won't cause running
+    //      script because of `AutoHideSelectionChanges` which blocks
+    //      selection change listeners and the selection change event
+    //      dispatcher.
+    MOZ_CAN_RUN_SCRIPT_BOUNDARY nsresult
+    ComputeRangesToDeleteAtOtherBlockBoundary(
+        const HTMLEditor& aHTMLEditor,
+        nsIEditor::EDirection aDirectionAndAmount,
+        const EditorDOMPoint& aCaretPoint, AutoRangeArray& aRangesToDelete,
+        const Element& aEditingHost) const;
+    [[nodiscard]] MOZ_CAN_RUN_SCRIPT Result<EditActionResult, nsresult>
+    JoinBlockElementsInSameParent(
+        HTMLEditor& aHTMLEditor, nsIEditor::EDirection aDirectionAndAmount,
+        nsIEditor::EStripWrappers aStripWrappers,
+        AutoRangeArray& aRangesToDelete,
+        AutoDeleteRangesHandler::SelectionWasCollapsed aSelectionWasCollapsed,
+        const Element& aEditingHost);
+    nsresult ComputeRangesToJoinBlockElementsInSameParent(
+        const HTMLEditor& aHTMLEditor,
+        nsIEditor::EDirection aDirectionAndAmount,
+        AutoRangeArray& aRangesToDelete) const;
+    [[nodiscard]] MOZ_CAN_RUN_SCRIPT Result<EditActionResult, nsresult>
+    DeleteBRElement(HTMLEditor& aHTMLEditor,
+                    nsIEditor::EDirection aDirectionAndAmount,
+                    const Element& aEditingHost);
+    nsresult ComputeRangesToDeleteBRElement(
+        AutoRangeArray& aRangesToDelete) const;
+    [[nodiscard]] MOZ_CAN_RUN_SCRIPT Result<EditActionResult, nsresult>
+    DeleteContentInRanges(HTMLEditor& aHTMLEditor,
+                          nsIEditor::EDirection aDirectionAndAmount,
+                          nsIEditor::EStripWrappers aStripWrappers,
+                          AutoRangeArray& aRangesToDelete);
+    nsresult ComputeRangesToDeleteContentInRanges(
+        const HTMLEditor& aHTMLEditor,
+        nsIEditor::EDirection aDirectionAndAmount,
+        AutoRangeArray& aRangesToDelete) const;
+    [[nodiscard]] MOZ_CAN_RUN_SCRIPT Result<EditActionResult, nsresult>
+    HandleDeleteNonCollapsedRanges(
+        HTMLEditor& aHTMLEditor, nsIEditor::EDirection aDirectionAndAmount,
+        nsIEditor::EStripWrappers aStripWrappers,
+        AutoRangeArray& aRangesToDelete,
+        AutoDeleteRangesHandler::SelectionWasCollapsed aSelectionWasCollapsed,
+        const Element& aEditingHost);
+    nsresult ComputeRangesToDeleteNonCollapsedRanges(
+        const HTMLEditor& aHTMLEditor,
+        nsIEditor::EDirection aDirectionAndAmount,
+        AutoRangeArray& aRangesToDelete,
+        AutoDeleteRangesHandler::SelectionWasCollapsed aSelectionWasCollapsed,
+        const Element& aEditingHost) const;
+
+    /**
+     * JoinNodesDeepWithTransaction() joins aLeftNode and aRightNode "deeply".
+     * First, they are joined simply, then, new right node is assumed as the
+     * child at length of the left node before joined and new left node is
+     * assumed as its previous sibling.  Then, they will be joined again.
+     * And then, these steps are repeated.
+     *
+     * @param aLeftContent    The node which will be removed form the tree.
+     * @param aRightContent   The node which will be inserted the contents of
+     *                        aRightContent.
+     * @return                The point of the first child of the last right
+     * node. The result is always set if this succeeded.
+     */
+    MOZ_CAN_RUN_SCRIPT Result<EditorDOMPoint, nsresult>
+    JoinNodesDeepWithTransaction(HTMLEditor& aHTMLEditor,
+                                 nsIContent& aLeftContent,
+                                 nsIContent& aRightContent);
+
+    /**
+     * DeleteNodesEntirelyInRangeButKeepTableStructure() removes nodes which are
+     * entirely in aRange.  Howevers, if some nodes are part of a table,
+     * removes all children of them instead.  I.e., this does not make damage to
+     * table structure at the range, but may remove table entirely if it's
+     * in the range.
+     *
+     * @return                  true if inclusive ancestor block elements at
+     *                          start and end of the range should be joined.
+     */
+    MOZ_CAN_RUN_SCRIPT Result<bool, nsresult>
+    DeleteNodesEntirelyInRangeButKeepTableStructure(
+        HTMLEditor& aHTMLEditor, nsRange& aRange,
+        AutoDeleteRangesHandler::SelectionWasCollapsed aSelectionWasCollapsed);
+    bool NeedsToJoinNodesAfterDeleteNodesEntirelyInRangeButKeepTableStructure(
+        const HTMLEditor& aHTMLEditor,
+        const nsTArray<OwningNonNull<nsIContent>>& aArrayOfContents,
+        AutoDeleteRangesHandler::SelectionWasCollapsed aSelectionWasCollapsed)
+        const;
+    Result<bool, nsresult>
+    ComputeRangesToDeleteNodesEntirelyInRangeButKeepTableStructure(
+        const HTMLEditor& aHTMLEditor, nsRange& aRange,
+        AutoDeleteRangesHandler::SelectionWasCollapsed aSelectionWasCollapsed)
+        const;
+
+    /**
+     * DeleteContentButKeepTableStructure() removes aContent if it's an element
+     * which is part of a table structure.  If it's a part of table structure,
+     * removes its all children recursively.  I.e., this may delete all of a
+     * table, but won't break table structure partially.
+     *
+     * @param aContent            The content which or whose all children should
+     *                            be removed.
+     */
+    [[nodiscard]] MOZ_CAN_RUN_SCRIPT nsresult
+    DeleteContentButKeepTableStructure(HTMLEditor& aHTMLEditor,
+                                       nsIContent& aContent);
+
+    /**
+     * DeleteTextAtStartAndEndOfRange() removes text if start and/or end of
+     * aRange is in a text node.
+     */
+    [[nodiscard]] MOZ_CAN_RUN_SCRIPT nsresult
+    DeleteTextAtStartAndEndOfRange(HTMLEditor& aHTMLEditor, nsRange& aRange);
+
+    class MOZ_STACK_CLASS AutoInclusiveAncestorBlockElementsJoiner final {
+     public:
+      AutoInclusiveAncestorBlockElementsJoiner() = delete;
+      AutoInclusiveAncestorBlockElementsJoiner(
+          nsIContent& aInclusiveDescendantOfLeftBlockElement,
+          nsIContent& aInclusiveDescendantOfRightBlockElement)
+          : mInclusiveDescendantOfLeftBlockElement(
+                aInclusiveDescendantOfLeftBlockElement),
+            mInclusiveDescendantOfRightBlockElement(
+                aInclusiveDescendantOfRightBlockElement),
+            mCanJoinBlocks(false),
+            mFallbackToDeleteLeafContent(false) {}
+
+      bool IsSet() const { return mLeftBlockElement && mRightBlockElement; }
+      bool IsSameBlockElement() const {
+        return mLeftBlockElement && mLeftBlockElement == mRightBlockElement;
+      }
+
+      const EditorDOMPoint& PointRefToPutCaret() const {
+        return mPointToPutCaret;
+      }
+
+      /**
+       * Prepare for joining inclusive ancestor block elements.  When this
+       * returns false, the deletion should be canceled.
+       */
+      Result<bool, nsresult> Prepare(const HTMLEditor& aHTMLEditor,
+                                     const Element& aEditingHost);
+
+      /**
+       * When this returns true, this can join the blocks with `Run()`.
+       */
+      bool CanJoinBlocks() const { return mCanJoinBlocks; }
+
+      /**
+       * When this returns true, `Run()` must return "ignored" so that
+       * caller can skip calling `Run()`.  This is available only when
+       * `CanJoinBlocks()` returns `true`.
+       * TODO: This should be merged into `CanJoinBlocks()` in the future.
+       */
+      bool ShouldDeleteLeafContentInstead() const {
+        MOZ_ASSERT(CanJoinBlocks());
+        return mFallbackToDeleteLeafContent;
+      }
+
+      /**
+       * ComputeRangesToDelete() extends aRangesToDelete includes the element
+       * boundaries between joining blocks.  If they won't be joined, this
+       * collapses the range to aCaretPoint.
+       */
+      nsresult ComputeRangesToDelete(const HTMLEditor& aHTMLEditor,
+                                     const EditorDOMPoint& aCaretPoint,
+                                     AutoRangeArray& aRangesToDelete) const;
+
+      /**
+       * Join inclusive ancestor block elements which are found by preceding
+       * Preare() call.
+       * The right element is always joined to the left element.
+       * If the elements are the same type and not nested within each other,
+       * JoinEditableNodesWithTransaction() is called (example, joining two
+       * list items together into one).
+       * If the elements are not the same type, or one is a descendant of the
+       * other, we instead destroy the right block placing its children into
+       * left block.
+       */
+      [[nodiscard]] MOZ_CAN_RUN_SCRIPT Result<EditActionResult, nsresult> Run(
+          HTMLEditor& aHTMLEditor, const Element& aEditingHost);
+
+     private:
+      /**
+       * This method returns true when
+       * `MergeFirstLineOfRightBlockElementIntoDescendantLeftBlockElement()`,
+       * `MergeFirstLineOfRightBlockElementIntoAncestorLeftBlockElement()` and
+       * `MergeFirstLineOfRightBlockElementIntoLeftBlockElement()` handle it
+       * with the `if` block of their main blocks.
+       */
+      bool CanMergeLeftAndRightBlockElements() const {
+        if (!IsSet()) {
+          return false;
+        }
+        // `MergeFirstLineOfRightBlockElementIntoDescendantLeftBlockElement()`
+        if (mPointContainingTheOtherBlockElement.GetContainer() ==
+            mRightBlockElement) {
+          return mNewListElementTagNameOfRightListElement.isSome();
+        }
+        // `MergeFirstLineOfRightBlockElementIntoAncestorLeftBlockElement()`
+        if (mPointContainingTheOtherBlockElement.GetContainer() ==
+            mLeftBlockElement) {
+          return mNewListElementTagNameOfRightListElement.isSome() &&
+                 !mRightBlockElement->GetChildCount();
+        }
+        MOZ_ASSERT(!mPointContainingTheOtherBlockElement.IsSet());
+        // `MergeFirstLineOfRightBlockElementIntoLeftBlockElement()`
+        return mNewListElementTagNameOfRightListElement.isSome() ||
+               mLeftBlockElement->NodeInfo()->NameAtom() ==
+                   mRightBlockElement->NodeInfo()->NameAtom();
+      }
+
+      OwningNonNull<nsIContent> mInclusiveDescendantOfLeftBlockElement;
+      OwningNonNull<nsIContent> mInclusiveDescendantOfRightBlockElement;
+      RefPtr<Element> mLeftBlockElement;
+      RefPtr<Element> mRightBlockElement;
+      Maybe<nsAtom*> mNewListElementTagNameOfRightListElement;
+      EditorDOMPoint mPointContainingTheOtherBlockElement;
+      EditorDOMPoint mPointToPutCaret;
+      RefPtr<dom::HTMLBRElement> mPrecedingInvisibleBRElement;
+      bool mCanJoinBlocks;
+      bool mFallbackToDeleteLeafContent;
+    };  // HTMLEditor::AutoDeleteRangesHandler::AutoBlockElementsJoiner::
+        // AutoInclusiveAncestorBlockElementsJoiner
+
+    enum class Mode {
+      NotInitialized,
+      JoinCurrentBlock,
+      JoinOtherBlock,
+      JoinBlocksInSameParent,
+      DeleteBRElement,
+      DeleteContentInRanges,
+      DeleteNonCollapsedRanges,
+    };
+    AutoDeleteRangesHandler* mDeleteRangesHandler;
+    const AutoDeleteRangesHandler& mDeleteRangesHandlerConst;
+    nsCOMPtr<nsIContent> mLeftContent;
+    nsCOMPtr<nsIContent> mRightContent;
+    nsCOMPtr<nsIContent> mLeafContentInOtherBlock;
+    // mSkippedInvisibleContents stores all content nodes which are skipped at
+    // scanning mLeftContent and mRightContent.  The content nodes should be
+    // removed at deletion.
+    AutoTArray<OwningNonNull<nsIContent>, 8> mSkippedInvisibleContents;
+    RefPtr<dom::HTMLBRElement> mBRElement;
+    Mode mMode = Mode::NotInitialized;
+  };  // HTMLEditor::AutoDeleteRangesHandler::AutoBlockElementsJoiner
+
+  class MOZ_STACK_CLASS AutoEmptyBlockAncestorDeleter final {
+   public:
+    /**
+     * ScanEmptyBlockInclusiveAncestor() scans an inclusive ancestor element
+     * which is empty and a block element.  Then, stores the result and
+     * returns the found empty block element.
+     *
+     * @param aHTMLEditor         The HTMLEditor.
+     * @param aStartContent       Start content to look for empty ancestors.
+     */
+    [[nodiscard]] Element* ScanEmptyBlockInclusiveAncestor(
+        const HTMLEditor& aHTMLEditor, nsIContent& aStartContent);
+
+    /**
+     * ComputeTargetRanges() computes "target ranges" for deleting
+     * `mEmptyInclusiveAncestorBlockElement`.
+     */
+    nsresult ComputeTargetRanges(const HTMLEditor& aHTMLEditor,
+                                 nsIEditor::EDirection aDirectionAndAmount,
+                                 const Element& aEditingHost,
+                                 AutoRangeArray& aRangesToDelete) const;
+
+    /**
+     * Deletes found empty block element by `ScanEmptyBlockInclusiveAncestor()`.
+     * If found one is a list item element, calls
+     * `MaybeInsertBRElementBeforeEmptyListItemElement()` before deleting
+     * the list item element.
+     * If found empty ancestor is not a list item element,
+     * `GetNewCaretPosition()` will be called to determine new caret position.
+     * Finally, removes the empty block ancestor.
+     *
+     * @param aHTMLEditor         The HTMLEditor.
+     * @param aDirectionAndAmount If found empty ancestor block is a list item
+     *                            element, this is ignored.  Otherwise:
+     *                            - If eNext, eNextWord or eToEndOfLine,
+     *                              collapse Selection to after found empty
+     *                              ancestor.
+     *                            - If ePrevious, ePreviousWord or
+     *                              eToBeginningOfLine, collapse Selection to
+     *                              end of previous editable node.
+     *                            - Otherwise, eNone is allowed but does
+     *                              nothing.
+     */
+    [[nodiscard]] MOZ_CAN_RUN_SCRIPT Result<EditActionResult, nsresult> Run(
+        HTMLEditor& aHTMLEditor, nsIEditor::EDirection aDirectionAndAmount);
+
+   private:
+    /**
+     * MaybeReplaceSubListWithNewListItem() replaces
+     * mEmptyInclusiveAncestorBlockElement with new list item element
+     * (containing <br>) if:
+     * - mEmptyInclusiveAncestorBlockElement is a list element
+     * - The parent of mEmptyInclusiveAncestorBlockElement is a list element
+     * - The parent becomes empty after deletion
+     * If this does not perform the replacement, returns "ignored".
+     */
+    [[nodiscard]] MOZ_CAN_RUN_SCRIPT Result<EditActionResult, nsresult>
+    MaybeReplaceSubListWithNewListItem(HTMLEditor& aHTMLEditor);
+
+    /**
+     * MaybeInsertBRElementBeforeEmptyListItemElement() inserts a `<br>` element
+     * if `mEmptyInclusiveAncestorBlockElement` is a list item element which
+     * is first editable element in its parent, and its grand parent is not a
+     * list element, inserts a `<br>` element before the empty list item.
+     */
+    [[nodiscard]] MOZ_CAN_RUN_SCRIPT Result<RefPtr<Element>, nsresult>
+    MaybeInsertBRElementBeforeEmptyListItemElement(HTMLEditor& aHTMLEditor);
+
+    /**
+     * GetNewCaretPosition() returns new caret position after deleting
+     * `mEmptyInclusiveAncestorBlockElement`.
+     */
+    [[nodiscard]] Result<CaretPoint, nsresult> GetNewCaretPosition(
+        const HTMLEditor& aHTMLEditor,
+        nsIEditor::EDirection aDirectionAndAmount) const;
+
+    RefPtr<Element> mEmptyInclusiveAncestorBlockElement;
+  };  // HTMLEditor::AutoDeleteRangesHandler::AutoEmptyBlockAncestorDeleter
+
+  const AutoDeleteRangesHandler* const mParent;
+  nsIEditor::EDirection mOriginalDirectionAndAmount;
+  nsIEditor::EStripWrappers mOriginalStripWrappers;
+};  // HTMLEditor::AutoDeleteRangesHandler
+
+nsresult HTMLEditor::ComputeTargetRanges(
+    nsIEditor::EDirection aDirectionAndAmount,
+    AutoRangeArray& aRangesToDelete) const {
+  MOZ_ASSERT(IsEditActionDataAvailable());
+
+  Element* editingHost = ComputeEditingHost();
+  if (!editingHost) {
+    aRangesToDelete.RemoveAllRanges();
+    return NS_ERROR_EDITOR_NO_EDITABLE_RANGE;
+  }
+
+  // First check for table selection mode.  If so, hand off to table editor.
+  SelectedTableCellScanner scanner(aRangesToDelete);
+  if (scanner.IsInTableCellSelectionMode()) {
+    // If it's in table cell selection mode, we'll delete all childen in
+    // the all selected table cell elements,
+    if (scanner.ElementsRef().Length() == aRangesToDelete.Ranges().Length()) {
+      return NS_OK;
+    }
+    // but will ignore all ranges which does not select a table cell.
+    size_t removedRanges = 0;
+    for (size_t i = 1; i < scanner.ElementsRef().Length(); i++) {
+      if (HTMLEditUtils::GetTableCellElementIfOnlyOneSelected(
+              aRangesToDelete.Ranges()[i - removedRanges]) !=
+          scanner.ElementsRef()[i]) {
+        // XXX Need to manage anchor-focus range too!
+        aRangesToDelete.Ranges().RemoveElementAt(i - removedRanges);
+        removedRanges++;
+      }
+    }
+    return NS_OK;
+  }
+
+  aRangesToDelete.EnsureOnlyEditableRanges(*editingHost);
+  if (aRangesToDelete.Ranges().IsEmpty()) {
+    NS_WARNING(
+        "There is no range which we can delete entire of or around the caret");
+    return NS_ERROR_EDITOR_NO_EDITABLE_RANGE;
+  }
+  AutoDeleteRangesHandler deleteHandler;
+  // Should we delete target ranges which cannot delete actually?
+  nsresult rv = deleteHandler.ComputeRangesToDelete(
+      *this, aDirectionAndAmount, aRangesToDelete, *editingHost);
+  NS_WARNING_ASSERTION(
+      NS_SUCCEEDED(rv),
+      "AutoDeleteRangesHandler::ComputeRangesToDelete() failed");
+  return rv;
+}
+
+Result<EditActionResult, nsresult> HTMLEditor::HandleDeleteSelection(
+    nsIEditor::EDirection aDirectionAndAmount,
+    nsIEditor::EStripWrappers aStripWrappers) {
+  MOZ_ASSERT(IsEditActionDataAvailable());
+  MOZ_ASSERT(aStripWrappers == nsIEditor::eStrip ||
+             aStripWrappers == nsIEditor::eNoStrip);
+
+  if (MOZ_UNLIKELY(!SelectionRef().RangeCount())) {
+    return Err(NS_ERROR_EDITOR_NO_EDITABLE_RANGE);
+  }
+
+  RefPtr<Element> editingHost = ComputeEditingHost();
+  if (MOZ_UNLIKELY(!editingHost)) {
+    return Err(NS_ERROR_EDITOR_NO_EDITABLE_RANGE);
+  }
+
+  // Remember that we did a selection deletion.  Used by
+  // CreateStyleForInsertText()
+  TopLevelEditSubActionDataRef().mDidDeleteSelection = true;
+
+  if (MOZ_UNLIKELY(IsEmpty())) {
+    return EditActionResult::CanceledResult();
+  }
+
+  // First check for table selection mode.  If so, hand off to table editor.
+  if (HTMLEditUtils::IsInTableCellSelectionMode(SelectionRef())) {
+    nsresult rv = DeleteTableCellContentsWithTransaction();
+    if (NS_WARN_IF(Destroyed())) {
+      return Err(NS_ERROR_EDITOR_DESTROYED);
+    }
+    if (NS_FAILED(rv)) {
+      NS_WARNING("HTMLEditor::DeleteTableCellContentsWithTransaction() failed");
+      return Err(rv);
+    }
+    return EditActionResult::HandledResult();
+  }
+
+  AutoRangeArray rangesToDelete(SelectionRef());
+  rangesToDelete.EnsureOnlyEditableRanges(*editingHost);
+  if (MOZ_UNLIKELY(rangesToDelete.Ranges().IsEmpty())) {
+    NS_WARNING(
+        "There is no range which we can delete entire the ranges or around the "
+        "caret");
+    return Err(NS_ERROR_EDITOR_NO_EDITABLE_RANGE);
+  }
+  AutoDeleteRangesHandler deleteHandler;
+  Result<EditActionResult, nsresult> result = deleteHandler.Run(
+      *this, aDirectionAndAmount, aStripWrappers, rangesToDelete, *editingHost);
+  if (MOZ_UNLIKELY(result.isErr()) || result.inspect().Canceled()) {
+    NS_WARNING_ASSERTION(result.isOk(),
+                         "AutoDeleteRangesHandler::Run() failed");
+    return result;
+  }
+
+  // XXX At here, selection may have no range because of mutation event
+  //     listeners can do anything so that we should just return NS_OK instead
+  //     of returning error.
+  const auto atNewStartOfSelection =
+      GetFirstSelectionStartPoint<EditorDOMPoint>();
+  if (NS_WARN_IF(!atNewStartOfSelection.IsSet())) {
+    return Err(NS_ERROR_FAILURE);
+  }
+  if (atNewStartOfSelection.IsInContentNode()) {
+    nsresult rv = DeleteMostAncestorMailCiteElementIfEmpty(
+        MOZ_KnownLive(*atNewStartOfSelection.ContainerAs<nsIContent>()));
+    if (NS_FAILED(rv)) {
+      NS_WARNING(
+          "HTMLEditor::DeleteMostAncestorMailCiteElementIfEmpty() failed");
+      return Err(rv);
+    }
+  }
+  return EditActionResult::HandledResult();
+}
+
+nsresult HTMLEditor::AutoDeleteRangesHandler::ComputeRangesToDelete(
+    const HTMLEditor& aHTMLEditor, nsIEditor::EDirection aDirectionAndAmount,
+    AutoRangeArray& aRangesToDelete, const Element& aEditingHost) {
+  MOZ_ASSERT(aHTMLEditor.IsEditActionDataAvailable());
+  MOZ_ASSERT(!aRangesToDelete.Ranges().IsEmpty());
+
+  mOriginalDirectionAndAmount = aDirectionAndAmount;
+  mOriginalStripWrappers = nsIEditor::eNoStrip;
+
+  if (aHTMLEditor.mPaddingBRElementForEmptyEditor) {
+    nsresult rv = aRangesToDelete.Collapse(
+        EditorRawDOMPoint(aHTMLEditor.mPaddingBRElementForEmptyEditor));
+    NS_WARNING_ASSERTION(NS_SUCCEEDED(rv), "AutoRangeArray::Collapse() failed");
+    return rv;
+  }
+
+  SelectionWasCollapsed selectionWasCollapsed = aRangesToDelete.IsCollapsed()
+                                                    ? SelectionWasCollapsed::Yes
+                                                    : SelectionWasCollapsed::No;
+  if (selectionWasCollapsed == SelectionWasCollapsed::Yes) {
+    const auto startPoint =
+        aRangesToDelete.GetFirstRangeStartPoint<EditorDOMPoint>();
+    if (NS_WARN_IF(!startPoint.IsSet())) {
+      return NS_ERROR_FAILURE;
+    }
+    RefPtr<Element> editingHost = aHTMLEditor.ComputeEditingHost();
+    if (NS_WARN_IF(!editingHost)) {
+      return NS_ERROR_FAILURE;
+    }
+    if (startPoint.IsInContentNode()) {
+      AutoEmptyBlockAncestorDeleter deleter;
+      if (deleter.ScanEmptyBlockInclusiveAncestor(
+              aHTMLEditor, *startPoint.ContainerAs<nsIContent>())) {
+        nsresult rv = deleter.ComputeTargetRanges(
+            aHTMLEditor, aDirectionAndAmount, *editingHost, aRangesToDelete);
+        NS_WARNING_ASSERTION(
+            NS_SUCCEEDED(rv),
+            "AutoEmptyBlockAncestorDeleter::ComputeTargetRanges() failed");
+        return rv;
+      }
+    }
+
+    // We shouldn't update caret bidi level right now, but we need to check
+    // whether the deletion will be canceled or not.
+    AutoCaretBidiLevelManager bidiLevelManager(aHTMLEditor, aDirectionAndAmount,
+                                               startPoint);
+    if (bidiLevelManager.Failed()) {
+      NS_WARNING(
+          "EditorBase::AutoCaretBidiLevelManager failed to initialize itself");
+      return NS_ERROR_FAILURE;
+    }
+    if (bidiLevelManager.Canceled()) {
+      return NS_SUCCESS_DOM_NO_OPERATION;
+    }
+
+    // AutoRangeArray::ExtendAnchorFocusRangeFor() will use `nsFrameSelection`
+    // to extend the range for deletion.  But if focus event doesn't receive
+    // yet, ancestor isn't set.  So we must set root element of editor to
+    // ancestor temporarily.
+    AutoSetTemporaryAncestorLimiter autoSetter(
+        aHTMLEditor, aHTMLEditor.SelectionRef(), *startPoint.GetContainer(),
+        &aRangesToDelete);
+
+    Result<nsIEditor::EDirection, nsresult> extendResult =
+        aRangesToDelete.ExtendAnchorFocusRangeFor(aHTMLEditor,
+                                                  aDirectionAndAmount);
+    if (extendResult.isErr()) {
+      NS_WARNING("AutoRangeArray::ExtendAnchorFocusRangeFor() failed");
+      return extendResult.unwrapErr();
+    }
+
+    // For compatibility with other browsers, we should set target ranges
+    // to start from and/or end after an atomic content rather than start
+    // from preceding text node end nor end at following text node start.
+    Result<bool, nsresult> shrunkenResult =
+        aRangesToDelete.ShrinkRangesIfStartFromOrEndAfterAtomicContent(
+            aHTMLEditor, aDirectionAndAmount,
+            AutoRangeArray::IfSelectingOnlyOneAtomicContent::Collapse,
+            editingHost);
+    if (shrunkenResult.isErr()) {
+      NS_WARNING(
+          "AutoRangeArray::ShrinkRangesIfStartFromOrEndAfterAtomicContent() "
+          "failed");
+      return shrunkenResult.unwrapErr();
+    }
+
+    if (!shrunkenResult.inspect() || !aRangesToDelete.IsCollapsed()) {
+      aDirectionAndAmount = extendResult.unwrap();
+    }
+
+    if (aDirectionAndAmount == nsIEditor::eNone) {
+      MOZ_ASSERT(aRangesToDelete.Ranges().Length() == 1);
+      if (!CanFallbackToDeleteRangesWithTransaction(aRangesToDelete)) {
+        // XXX In this case, do we need to modify the range again?
+        return NS_SUCCESS_DOM_NO_OPERATION;
+      }
+      nsresult rv = FallbackToComputeRangesToDeleteRangesWithTransaction(
+          aHTMLEditor, aRangesToDelete);
+      NS_WARNING_ASSERTION(
+          NS_SUCCEEDED(rv),
+          "AutoDeleteRangesHandler::"
+          "FallbackToComputeRangesToDeleteRangesWithTransaction() failed");
+      return rv;
+    }
+
+    if (aRangesToDelete.IsCollapsed()) {
+      const auto caretPoint =
+          aRangesToDelete.GetFirstRangeStartPoint<EditorDOMPoint>();
+      if (MOZ_UNLIKELY(NS_WARN_IF(!caretPoint.IsInContentNode()))) {
+        return NS_ERROR_FAILURE;
+      }
+      if (!EditorUtils::IsEditableContent(*caretPoint.ContainerAs<nsIContent>(),
+                                          EditorType::HTML)) {
+        return NS_SUCCESS_DOM_NO_OPERATION;
+      }
+      WSRunScanner wsRunScannerAtCaret(editingHost, caretPoint);
+      WSScanResult scanFromCaretPointResult =
+          aDirectionAndAmount == nsIEditor::eNext
+              ? wsRunScannerAtCaret.ScanNextVisibleNodeOrBlockBoundaryFrom(
+                    caretPoint)
+              : wsRunScannerAtCaret.ScanPreviousVisibleNodeOrBlockBoundaryFrom(
+                    caretPoint);
+      if (scanFromCaretPointResult.Failed()) {
+        NS_WARNING(
+            "WSRunScanner::Scan(Next|Previous)VisibleNodeOrBlockBoundaryFrom() "
+            "failed");
+        return NS_ERROR_FAILURE;
+      }
+      if (!scanFromCaretPointResult.GetContent()) {
+        return NS_SUCCESS_DOM_NO_OPERATION;
+      }
+
+      if (scanFromCaretPointResult.ReachedBRElement()) {
+        if (scanFromCaretPointResult.BRElementPtr() ==
+            wsRunScannerAtCaret.GetEditingHost()) {
+          return NS_OK;
+        }
+        if (!EditorUtils::IsEditableContent(
+                *scanFromCaretPointResult.BRElementPtr(), EditorType::HTML)) {
+          return NS_SUCCESS_DOM_NO_OPERATION;
+        }
+        if (HTMLEditUtils::IsInvisibleBRElement(
+                *scanFromCaretPointResult.BRElementPtr())) {
+          EditorDOMPoint newCaretPosition =
+              aDirectionAndAmount == nsIEditor::eNext
+                  ? EditorDOMPoint::After(
+                        *scanFromCaretPointResult.BRElementPtr())
+                  : EditorDOMPoint(scanFromCaretPointResult.BRElementPtr());
+          if (NS_WARN_IF(!newCaretPosition.IsSet())) {
+            return NS_ERROR_FAILURE;
+          }
+          AutoHideSelectionChanges blockSelectionListeners(
+              aHTMLEditor.SelectionRef());
+          nsresult rv = aHTMLEditor.CollapseSelectionTo(newCaretPosition);
+          if (MOZ_UNLIKELY(NS_FAILED(rv))) {
+            NS_WARNING("EditorBase::CollapseSelectionTo() failed");
+            return NS_ERROR_FAILURE;
+          }
+          if (NS_WARN_IF(!aHTMLEditor.SelectionRef().RangeCount())) {
+            return NS_ERROR_UNEXPECTED;
+          }
+          aRangesToDelete.Initialize(aHTMLEditor.SelectionRef());
+          AutoDeleteRangesHandler anotherHandler(this);
+          rv = anotherHandler.ComputeRangesToDelete(
+              aHTMLEditor, aDirectionAndAmount, aRangesToDelete, aEditingHost);
+          NS_WARNING_ASSERTION(
+              NS_SUCCEEDED(rv),
+              "Recursive AutoDeleteRangesHandler::ComputeRangesToDelete() "
+              "failed");
+
+          rv = aHTMLEditor.CollapseSelectionTo(caretPoint);
+          if (MOZ_UNLIKELY(rv == NS_ERROR_EDITOR_DESTROYED)) {
+            NS_WARNING(
+                "EditorBase::CollapseSelectionTo() caused destroying the "
+                "editor");
+            return NS_ERROR_EDITOR_DESTROYED;
+          }
+          NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                               "EditorBase::CollapseSelectionTo() failed to "
+                               "restore original selection, but ignored");
+
+          MOZ_ASSERT(aRangesToDelete.Ranges().Length() == 1);
+          // If the range is collapsed, there is no content which should
+          // be removed together.  In this case, only the invisible `<br>`
+          // element should be selected.
+          if (aRangesToDelete.IsCollapsed()) {
+            nsresult rv = aRangesToDelete.SelectNode(
+                *scanFromCaretPointResult.BRElementPtr());
+            NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                                 "AutoRangeArray::SelectNode() failed");
+            return rv;
+          }
+
+          // Otherwise, extend the range to contain the invisible `<br>`
+          // element.
+          if (EditorRawDOMPoint(scanFromCaretPointResult.BRElementPtr())
+                  .IsBefore(
+                      aRangesToDelete
+                          .GetFirstRangeStartPoint<EditorRawDOMPoint>())) {
+            nsresult rv = aRangesToDelete.FirstRangeRef()->SetStartAndEnd(
+                EditorRawDOMPoint(scanFromCaretPointResult.BRElementPtr())
+                    .ToRawRangeBoundary(),
+                aRangesToDelete.FirstRangeRef()->EndRef());
+            NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                                 "nsRange::SetStartAndEnd() failed");
+            return rv;
+          }
+          if (aRangesToDelete.GetFirstRangeEndPoint<EditorRawDOMPoint>()
+                  .IsBefore(EditorRawDOMPoint::After(
+                      *scanFromCaretPointResult.BRElementPtr()))) {
+            nsresult rv = aRangesToDelete.FirstRangeRef()->SetStartAndEnd(
+                aRangesToDelete.FirstRangeRef()->StartRef(),
+                EditorRawDOMPoint::After(
+                    *scanFromCaretPointResult.BRElementPtr())
+                    .ToRawRangeBoundary());
+            NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                                 "nsRange::SetStartAndEnd() failed");
+            return rv;
+          }
+          NS_WARNING("Was the invisible `<br>` element selected?");
+          return NS_OK;
+        }
+      }
+
+      nsresult rv = ComputeRangesToDeleteAroundCollapsedRanges(
+          aHTMLEditor, aDirectionAndAmount, aRangesToDelete,
+          wsRunScannerAtCaret, scanFromCaretPointResult, aEditingHost);
+      NS_WARNING_ASSERTION(
+          NS_SUCCEEDED(rv),
+          "AutoDeleteRangesHandler::ComputeRangesToDeleteAroundCollapsedRanges("
+          ") failed");
+      return rv;
+    }
+  }
+
+  nsresult rv = ComputeRangesToDeleteNonCollapsedRanges(
+      aHTMLEditor, aDirectionAndAmount, aRangesToDelete, selectionWasCollapsed,
+      aEditingHost);
+  NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                       "AutoDeleteRangesHandler::"
+                       "ComputeRangesToDeleteNonCollapsedRanges() failed");
+  return rv;
+}
+
+Result<EditActionResult, nsresult> HTMLEditor::AutoDeleteRangesHandler::Run(
+    HTMLEditor& aHTMLEditor, nsIEditor::EDirection aDirectionAndAmount,
+    nsIEditor::EStripWrappers aStripWrappers, AutoRangeArray& aRangesToDelete,
+    const Element& aEditingHost) {
+  MOZ_ASSERT(aHTMLEditor.IsEditActionDataAvailable());
+  MOZ_ASSERT(aStripWrappers == nsIEditor::eStrip ||
+             aStripWrappers == nsIEditor::eNoStrip);
+  MOZ_ASSERT(!aRangesToDelete.Ranges().IsEmpty());
+
+  mOriginalDirectionAndAmount = aDirectionAndAmount;
+  mOriginalStripWrappers = aStripWrappers;
+
+  if (MOZ_UNLIKELY(aHTMLEditor.IsEmpty())) {
+    return EditActionResult::CanceledResult();
+  }
+
+  // selectionWasCollapsed is used later to determine whether we should join
+  // blocks in HandleDeleteNonCollapsedRanges(). We don't really care about
+  // collapsed because it will be modified by
+  // AutoRangeArray::ExtendAnchorFocusRangeFor() later.
+  // AutoBlockElementsJoiner::AutoInclusiveAncestorBlockElementsJoiner should
+  // happen if the original selection is collapsed and the cursor is at the end
+  // of a block element, in which case
+  // AutoRangeArray::ExtendAnchorFocusRangeFor() would always make the selection
+  // not collapsed.
+  SelectionWasCollapsed selectionWasCollapsed = aRangesToDelete.IsCollapsed()
+                                                    ? SelectionWasCollapsed::Yes
+                                                    : SelectionWasCollapsed::No;
+
+  if (selectionWasCollapsed == SelectionWasCollapsed::Yes) {
+    const auto startPoint =
+        aRangesToDelete.GetFirstRangeStartPoint<EditorDOMPoint>();
+    if (NS_WARN_IF(!startPoint.IsSet())) {
+      return Err(NS_ERROR_FAILURE);
+    }
+
+    // If we are inside an empty block, delete it.
+    if (startPoint.IsInContentNode()) {
+#ifdef DEBUG
+      nsMutationGuard debugMutation;
+#endif  // #ifdef DEBUG
+      AutoEmptyBlockAncestorDeleter deleter;
+      if (deleter.ScanEmptyBlockInclusiveAncestor(
+              aHTMLEditor, *startPoint.ContainerAs<nsIContent>())) {
+        Result<EditActionResult, nsresult> result =
+            deleter.Run(aHTMLEditor, aDirectionAndAmount);
+        if (MOZ_UNLIKELY(result.isErr()) || result.inspect().Handled()) {
+          NS_WARNING_ASSERTION(result.isOk(),
+                               "AutoEmptyBlockAncestorDeleter::Run() failed");
+          return result;
+        }
+      }
+      MOZ_ASSERT(!debugMutation.Mutated(0),
+                 "AutoEmptyBlockAncestorDeleter shouldn't modify the DOM tree "
+                 "if it returns not handled nor error");
+    }
+
+    // Test for distance between caret and text that will be deleted.
+    // Note that this call modifies `nsFrameSelection` without modifying
+    // `Selection`.  However, it does not have problem for now because
+    // it'll be referred by `AutoRangeArray::ExtendAnchorFocusRangeFor()`
+    // before modifying `Selection`.
+    // XXX This looks odd.  `ExtendAnchorFocusRangeFor()` will extend
+    //     anchor-focus range, but here refers the first range.
+    AutoCaretBidiLevelManager bidiLevelManager(aHTMLEditor, aDirectionAndAmount,
+                                               startPoint);
+    if (MOZ_UNLIKELY(bidiLevelManager.Failed())) {
+      NS_WARNING(
+          "EditorBase::AutoCaretBidiLevelManager failed to initialize itself");
+      return Err(NS_ERROR_FAILURE);
+    }
+    bidiLevelManager.MaybeUpdateCaretBidiLevel(aHTMLEditor);
+    if (bidiLevelManager.Canceled()) {
+      return EditActionResult::CanceledResult();
+    }
+
+    // AutoRangeArray::ExtendAnchorFocusRangeFor() will use `nsFrameSelection`
+    // to extend the range for deletion.  But if focus event doesn't receive
+    // yet, ancestor isn't set.  So we must set root element of editor to
+    // ancestor temporarily.
+    AutoSetTemporaryAncestorLimiter autoSetter(
+        aHTMLEditor, aHTMLEditor.SelectionRef(), *startPoint.GetContainer(),
+        &aRangesToDelete);
+
+    // Calling `ExtendAnchorFocusRangeFor()` and
+    // `ShrinkRangesIfStartFromOrEndAfterAtomicContent()` may move caret to
+    // the container of deleting atomic content.  However, it may be different
+    // from the original caret's container.  The original caret container may
+    // be important to put caret after deletion so that let's cache the
+    // original position.
+    Maybe<EditorDOMPoint> caretPoint;
+    if (aRangesToDelete.IsCollapsed() && !aRangesToDelete.Ranges().IsEmpty()) {
+      caretPoint =
+          Some(aRangesToDelete.GetFirstRangeStartPoint<EditorDOMPoint>());
+      if (NS_WARN_IF(!caretPoint.ref().IsInContentNode())) {
+        return Err(NS_ERROR_FAILURE);
+      }
+    }
+
+    Result<nsIEditor::EDirection, nsresult> extendResult =
+        aRangesToDelete.ExtendAnchorFocusRangeFor(aHTMLEditor,
+                                                  aDirectionAndAmount);
+    if (MOZ_UNLIKELY(extendResult.isErr())) {
+      NS_WARNING("AutoRangeArray::ExtendAnchorFocusRangeFor() failed");
+      return extendResult.propagateErr();
+    }
+    if (caretPoint.isSome() &&
+        MOZ_UNLIKELY(!caretPoint.ref().IsSetAndValid())) {
+      NS_WARNING("The caret position became invalid");
+      return Err(NS_ERROR_EDITOR_UNEXPECTED_DOM_TREE);
+    }
+
+    // If there is only one range and it selects an atomic content, we should
+    // delete it with collapsed range path for making consistent behavior
+    // between both cases, the content is selected case and caret is at it or
+    // after it case.
+    Result<bool, nsresult> shrunkenResult =
+        aRangesToDelete.ShrinkRangesIfStartFromOrEndAfterAtomicContent(
+            aHTMLEditor, aDirectionAndAmount,
+            AutoRangeArray::IfSelectingOnlyOneAtomicContent::Collapse,
+            &aEditingHost);
+    if (MOZ_UNLIKELY(shrunkenResult.isErr())) {
+      NS_WARNING(
+          "AutoRangeArray::ShrinkRangesIfStartFromOrEndAfterAtomicContent() "
+          "failed");
+      return shrunkenResult.propagateErr();
+    }
+
+    if (!shrunkenResult.inspect() || !aRangesToDelete.IsCollapsed()) {
+      aDirectionAndAmount = extendResult.unwrap();
+    }
+
+    if (aDirectionAndAmount == nsIEditor::eNone) {
+      MOZ_ASSERT(aRangesToDelete.Ranges().Length() == 1);
+      if (!CanFallbackToDeleteRangesWithTransaction(aRangesToDelete)) {
+        return EditActionResult::IgnoredResult();
+      }
+      Result<CaretPoint, nsresult> caretPointOrError =
+          FallbackToDeleteRangesWithTransaction(aHTMLEditor, aRangesToDelete);
+      if (MOZ_UNLIKELY(caretPointOrError.isErr())) {
+        NS_WARNING(
+            "AutoDeleteRangesHandler::FallbackToDeleteRangesWithTransaction() "
+            "failed");
+      }
+      nsresult rv = caretPointOrError.inspect().SuggestCaretPointTo(
+          aHTMLEditor, {SuggestCaret::OnlyIfHasSuggestion,
+                        SuggestCaret::OnlyIfTransactionsAllowedToDoIt,
+                        SuggestCaret::AndIgnoreTrivialError});
+      if (NS_FAILED(rv)) {
+        NS_WARNING("CaretPoint::SuggestCaretPointTo() failed");
+        return Err(rv);
+      }
+      NS_WARNING_ASSERTION(
+          rv != NS_SUCCESS_EDITOR_BUT_IGNORED_TRIVIAL_ERROR,
+          "CaretPoint::SuggestCaretPointTo() failed, but ignored");
+      // Don't return "ignored" to avoid to fall it back to delete ranges
+      // recursively.
+      return EditActionResult::HandledResult();
+    }
+
+    if (aRangesToDelete.IsCollapsed()) {
+      // Use the original caret position for handling the deletion around
+      // collapsed range because the container may be different from the
+      // new collapsed position's container.
+      if (!EditorUtils::IsEditableContent(
+              *caretPoint.ref().ContainerAs<nsIContent>(), EditorType::HTML)) {
+        return EditActionResult::CanceledResult();
+      }
+      WSRunScanner wsRunScannerAtCaret(&aEditingHost, caretPoint.ref());
+      WSScanResult scanFromCaretPointResult =
+          aDirectionAndAmount == nsIEditor::eNext
+              ? wsRunScannerAtCaret.ScanNextVisibleNodeOrBlockBoundaryFrom(
+                    caretPoint.ref())
+              : wsRunScannerAtCaret.ScanPreviousVisibleNodeOrBlockBoundaryFrom(
+                    caretPoint.ref());
+      if (MOZ_UNLIKELY(scanFromCaretPointResult.Failed())) {
+        NS_WARNING(
+            "WSRunScanner::Scan(Next|Previous)VisibleNodeOrBlockBoundaryFrom() "
+            "failed");
+        return Err(NS_ERROR_FAILURE);
+      }
+      if (!scanFromCaretPointResult.GetContent()) {
+        return EditActionResult::CanceledResult();
+      }
+      // Short circuit for invisible breaks.  delete them and recurse.
+      if (scanFromCaretPointResult.ReachedBRElement()) {
+        if (scanFromCaretPointResult.BRElementPtr() == &aEditingHost) {
+          return EditActionResult::HandledResult();
+        }
+        if (!EditorUtils::IsEditableContent(
+                *scanFromCaretPointResult.BRElementPtr(), EditorType::HTML)) {
+          return EditActionResult::CanceledResult();
+        }
+        if (HTMLEditUtils::IsInvisibleBRElement(
+                *scanFromCaretPointResult.BRElementPtr())) {
+          // TODO: We should extend the range to delete again before/after
+          //       the caret point and use `HandleDeleteNonCollapsedRanges()`
+          //       instead after we would create delete range computation
+          //       method at switching to the new white-space normalizer.
+          Result<CaretPoint, nsresult> caretPointOrError =
+              WhiteSpaceVisibilityKeeper::
+                  DeleteContentNodeAndJoinTextNodesAroundIt(
+                      aHTMLEditor,
+                      MOZ_KnownLive(*scanFromCaretPointResult.BRElementPtr()),
+                      caretPoint.ref(), aEditingHost);
+          if (MOZ_UNLIKELY(caretPointOrError.isErr())) {
+            NS_WARNING(
+                "WhiteSpaceVisibilityKeeper::"
+                "DeleteContentNodeAndJoinTextNodesAroundIt() failed");
+            return caretPointOrError.propagateErr();
+          }
+          if (caretPointOrError.inspect().HasCaretPointSuggestion()) {
+            caretPoint = Some(caretPointOrError.unwrap().UnwrapCaretPoint());
+          }
+          if (NS_WARN_IF(!caretPoint->IsSetAndValid())) {
+            return Err(NS_ERROR_FAILURE);
+          }
+          AutoRangeArray rangesToDelete(caretPoint.ref());
+          if (aHTMLEditor.MayHaveMutationEventListeners(
+                  NS_EVENT_BITS_MUTATION_SUBTREEMODIFIED |
+                  NS_EVENT_BITS_MUTATION_NODEREMOVED |
+                  NS_EVENT_BITS_MUTATION_NODEREMOVEDFROMDOCUMENT)) {
+            // Let's check whether there is new invisible `<br>` element
+            // for avoiding infinite recursive calls.
+            WSRunScanner wsRunScannerAtCaret(&aEditingHost, caretPoint.ref());
+            WSScanResult scanFromCaretPointResult =
+                aDirectionAndAmount == nsIEditor::eNext
+                    ? wsRunScannerAtCaret
+                          .ScanNextVisibleNodeOrBlockBoundaryFrom(
+                              caretPoint.ref())
+                    : wsRunScannerAtCaret
+                          .ScanPreviousVisibleNodeOrBlockBoundaryFrom(
+                              caretPoint.ref());
+            if (MOZ_UNLIKELY(scanFromCaretPointResult.Failed())) {
+              NS_WARNING(
+                  "WSRunScanner::Scan(Next|Previous)"
+                  "VisibleNodeOrBlockBoundaryFrom() failed");
+              return Err(NS_ERROR_FAILURE);
+            }
+            if (MOZ_UNLIKELY(
+                    scanFromCaretPointResult.ReachedInvisibleBRElement())) {
+              return Err(NS_ERROR_EDITOR_UNEXPECTED_DOM_TREE);
+            }
+          }
+          AutoDeleteRangesHandler anotherHandler(this);
+          Result<EditActionResult, nsresult> result =
+              anotherHandler.Run(aHTMLEditor, aDirectionAndAmount,
+                                 aStripWrappers, rangesToDelete, aEditingHost);
+          NS_WARNING_ASSERTION(
+              result.isOk(), "Recursive AutoDeleteRangesHandler::Run() failed");
+          return result;
+        }
+      }
+
+      Result<EditActionResult, nsresult> result =
+          HandleDeleteAroundCollapsedRanges(
+              aHTMLEditor, aDirectionAndAmount, aStripWrappers, aRangesToDelete,
+              wsRunScannerAtCaret, scanFromCaretPointResult, aEditingHost);
+      NS_WARNING_ASSERTION(result.isOk(),
+                           "AutoDeleteRangesHandler::"
+                           "HandleDeleteAroundCollapsedRanges() failed");
+      return result;
+    }
+  }
+
+  Result<EditActionResult, nsresult> result = HandleDeleteNonCollapsedRanges(
+      aHTMLEditor, aDirectionAndAmount, aStripWrappers, aRangesToDelete,
+      selectionWasCollapsed, aEditingHost);
+  NS_WARNING_ASSERTION(
+      result.isOk(),
+      "AutoDeleteRangesHandler::HandleDeleteNonCollapsedRanges() failed");
+  return result;
+}
+
+nsresult
+HTMLEditor::AutoDeleteRangesHandler::ComputeRangesToDeleteAroundCollapsedRanges(
+    const HTMLEditor& aHTMLEditor, nsIEditor::EDirection aDirectionAndAmount,
+    AutoRangeArray& aRangesToDelete, const WSRunScanner& aWSRunScannerAtCaret,
+    const WSScanResult& aScanFromCaretPointResult,
+    const Element& aEditingHost) const {
+  if (aScanFromCaretPointResult.InCollapsibleWhiteSpaces() ||
+      aScanFromCaretPointResult.InNonCollapsibleCharacters() ||
+      aScanFromCaretPointResult.ReachedPreformattedLineBreak()) {
+    nsresult rv = aRangesToDelete.Collapse(
+        aScanFromCaretPointResult.Point<EditorRawDOMPoint>());
+    if (MOZ_UNLIKELY(NS_FAILED(rv))) {
+      NS_WARNING("AutoRangeArray::Collapse() failed");
+      return NS_ERROR_FAILURE;
+    }
+    rv = ComputeRangesToDeleteTextAroundCollapsedRanges(
+        aDirectionAndAmount, aRangesToDelete, aEditingHost);
+    NS_WARNING_ASSERTION(
+        NS_SUCCEEDED(rv),
+        "AutoDeleteRangesHandler::"
+        "ComputeRangesToDeleteTextAroundCollapsedRanges() failed");
+    return rv;
+  }
+
+  if (aScanFromCaretPointResult.ReachedSpecialContent() ||
+      aScanFromCaretPointResult.ReachedBRElement() ||
+      aScanFromCaretPointResult.ReachedHRElement() ||
+      aScanFromCaretPointResult.ReachedNonEditableOtherBlockElement()) {
+    if (aScanFromCaretPointResult.GetContent() ==
+        aWSRunScannerAtCaret.GetEditingHost()) {
+      return NS_OK;
+    }
+    nsIContent* atomicContent = GetAtomicContentToDelete(
+        aDirectionAndAmount, aWSRunScannerAtCaret, aScanFromCaretPointResult);
+    if (!HTMLEditUtils::IsRemovableNode(*atomicContent)) {
+      NS_WARNING(
+          "AutoDeleteRangesHandler::GetAtomicContentToDelete() cannot find "
+          "removable atomic content");
+      return NS_ERROR_FAILURE;
+    }
+    nsresult rv = ComputeRangesToDeleteAtomicContent(
+        aWSRunScannerAtCaret.GetEditingHost(), *atomicContent, aRangesToDelete);
+    NS_WARNING_ASSERTION(
+        NS_SUCCEEDED(rv),
+        "AutoDeleteRangesHandler::ComputeRangesToDeleteAtomicContent() failed");
+    return rv;
+  }
+
+  if (aScanFromCaretPointResult.ReachedOtherBlockElement()) {
+    if (NS_WARN_IF(!aScanFromCaretPointResult.GetContent()->IsElement())) {
+      return NS_ERROR_FAILURE;
+    }
+    AutoBlockElementsJoiner joiner(*this);
+    if (!joiner.PrepareToDeleteAtOtherBlockBoundary(
+            aHTMLEditor, aDirectionAndAmount,
+            *aScanFromCaretPointResult.ElementPtr(),
+            aWSRunScannerAtCaret.ScanStartRef(), aWSRunScannerAtCaret)) {
+      return NS_SUCCESS_DOM_NO_OPERATION;
+    }
+    nsresult rv = joiner.ComputeRangesToDelete(
+        aHTMLEditor, aDirectionAndAmount, aWSRunScannerAtCaret.ScanStartRef(),
+        aRangesToDelete, aEditingHost);
+    NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                         "AutoBlockElementsJoiner::ComputeRangesToDelete() "
+                         "failed (other block boundary)");
+    return rv;
+  }
+
+  if (aScanFromCaretPointResult.ReachedCurrentBlockBoundary()) {
+    if (NS_WARN_IF(!aScanFromCaretPointResult.GetContent()->IsElement())) {
+      return NS_ERROR_FAILURE;
+    }
+    AutoBlockElementsJoiner joiner(*this);
+    if (!joiner.PrepareToDeleteAtCurrentBlockBoundary(
+            aHTMLEditor, aDirectionAndAmount,
+            *aScanFromCaretPointResult.ElementPtr(),
+            aWSRunScannerAtCaret.ScanStartRef())) {
+      return NS_SUCCESS_DOM_NO_OPERATION;
+    }
+    nsresult rv = joiner.ComputeRangesToDelete(
+        aHTMLEditor, aDirectionAndAmount, aWSRunScannerAtCaret.ScanStartRef(),
+        aRangesToDelete, aEditingHost);
+    NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                         "AutoBlockElementsJoiner::ComputeRangesToDelete() "
+                         "failed (current block boundary)");
+    return rv;
+  }
+
+  return NS_OK;
+}
+
+Result<EditActionResult, nsresult>
+HTMLEditor::AutoDeleteRangesHandler::HandleDeleteAroundCollapsedRanges(
+    HTMLEditor& aHTMLEditor, nsIEditor::EDirection aDirectionAndAmount,
+    nsIEditor::EStripWrappers aStripWrappers, AutoRangeArray& aRangesToDelete,
+    const WSRunScanner& aWSRunScannerAtCaret,
+    const WSScanResult& aScanFromCaretPointResult,
+    const Element& aEditingHost) {
+  MOZ_ASSERT(aHTMLEditor.IsTopLevelEditSubActionDataAvailable());
+  MOZ_ASSERT(aRangesToDelete.IsCollapsed());
+  MOZ_ASSERT(aDirectionAndAmount != nsIEditor::eNone);
+  MOZ_ASSERT(aWSRunScannerAtCaret.ScanStartRef().IsInContentNode());
+  MOZ_ASSERT(EditorUtils::IsEditableContent(
+      *aWSRunScannerAtCaret.ScanStartRef().ContainerAs<nsIContent>(),
+      EditorType::HTML));
+
+  if (StaticPrefs::editor_white_space_normalization_blink_compatible()) {
+    if (aScanFromCaretPointResult.InCollapsibleWhiteSpaces() ||
+        aScanFromCaretPointResult.InNonCollapsibleCharacters() ||
+        aScanFromCaretPointResult.ReachedPreformattedLineBreak()) {
+      nsresult rv = aRangesToDelete.Collapse(
+          aScanFromCaretPointResult.Point<EditorRawDOMPoint>());
+      if (NS_FAILED(rv)) {
+        NS_WARNING("AutoRangeArray::Collapse() failed");
+        return Err(NS_ERROR_FAILURE);
+      }
+      Result<CaretPoint, nsresult> caretPointOrError =
+          HandleDeleteTextAroundCollapsedRanges(
+              aHTMLEditor, aDirectionAndAmount, aRangesToDelete, aEditingHost);
+      if (MOZ_UNLIKELY(caretPointOrError.isErr())) {
+        NS_WARNING(
+            "AutoDeleteRangesHandler::HandleDeleteTextAroundCollapsedRanges() "
+            "failed");
+        return caretPointOrError.propagateErr();
+      }
+      rv = caretPointOrError.unwrap().SuggestCaretPointTo(
+          aHTMLEditor, {SuggestCaret::OnlyIfHasSuggestion,
+                        SuggestCaret::OnlyIfTransactionsAllowedToDoIt,
+                        SuggestCaret::AndIgnoreTrivialError});
+      if (NS_FAILED(rv)) {
+        NS_WARNING("CaretPoint::SuggestCaretPointTo() failed");
+        return Err(rv);
+      }
+      NS_WARNING_ASSERTION(
+          rv != NS_SUCCESS_EDITOR_BUT_IGNORED_TRIVIAL_ERROR,
+          "CaretPoint::SuggestCaretPoint() failed, but ignored");
+      return EditActionResult::HandledResult();
+    }
+  }
+
+  if (aScanFromCaretPointResult.InCollapsibleWhiteSpaces() ||
+      aScanFromCaretPointResult.ReachedPreformattedLineBreak()) {
+    Result<CaretPoint, nsresult> caretPointOrError =
+        HandleDeleteCollapsedSelectionAtWhiteSpaces(
+            aHTMLEditor, aDirectionAndAmount,
+            aWSRunScannerAtCaret.ScanStartRef(), aEditingHost);
+    if (MOZ_UNLIKELY(caretPointOrError.isErr())) {
+      NS_WARNING(
+          "AutoDeleteRangesHandler::"
+          "HandleDeleteCollapsedSelectionAtWhiteSpaces() failed");
+      return caretPointOrError.propagateErr();
+    }
+    nsresult rv = caretPointOrError.unwrap().SuggestCaretPointTo(
+        aHTMLEditor, {SuggestCaret::OnlyIfHasSuggestion});
+    if (NS_FAILED(rv)) {
+      NS_WARNING("CaretPoint::SuggestCaretPointTo() failed");
+      return Err(rv);
+    }
+    NS_WARNING_ASSERTION(
+        rv != NS_SUCCESS_EDITOR_BUT_IGNORED_TRIVIAL_ERROR,
+        "CaretPoint::SuggestCaretPointTo() failed, but ignored");
+    return EditActionResult::HandledResult();
+  }
+
+  if (aScanFromCaretPointResult.InNonCollapsibleCharacters()) {
+    if (NS_WARN_IF(!aScanFromCaretPointResult.GetContent()->IsText())) {
+      return Err(NS_ERROR_FAILURE);
+    }
+    Result<CaretPoint, nsresult> caretPointOrError =
+        HandleDeleteCollapsedSelectionAtVisibleChar(
+            aHTMLEditor, aDirectionAndAmount, aRangesToDelete,
+            aScanFromCaretPointResult.Point<EditorDOMPoint>(), aEditingHost);
+    if (MOZ_UNLIKELY(caretPointOrError.isErr())) {
+      NS_WARNING(
+          "AutoDeleteRangesHandler::"
+          "HandleDeleteCollapsedSelectionAtVisibleChar() failed");
+      return caretPointOrError.propagateErr();
+    }
+    nsresult rv = caretPointOrError.unwrap().SuggestCaretPointTo(
+        aHTMLEditor, {SuggestCaret::OnlyIfHasSuggestion});
+    if (NS_FAILED(rv)) {
+      NS_WARNING("CaretPoint::SuggestCaretPointTo() failed");
+      return Err(rv);
+    }
+    NS_WARNING_ASSERTION(
+        rv != NS_SUCCESS_EDITOR_BUT_IGNORED_TRIVIAL_ERROR,
+        "CaretPoint::SuggestCaretPointTo() failed, but ignored");
+    return EditActionResult::HandledResult();
+  }
+
+  if (aScanFromCaretPointResult.ReachedSpecialContent() ||
+      aScanFromCaretPointResult.ReachedBRElement() ||
+      aScanFromCaretPointResult.ReachedHRElement() ||
+      aScanFromCaretPointResult.ReachedNonEditableOtherBlockElement()) {
+    if (aScanFromCaretPointResult.GetContent() == &aEditingHost) {
+      return EditActionResult::HandledResult();
+    }
+    nsCOMPtr<nsIContent> atomicContent = GetAtomicContentToDelete(
+        aDirectionAndAmount, aWSRunScannerAtCaret, aScanFromCaretPointResult);
+    if (MOZ_UNLIKELY(!HTMLEditUtils::IsRemovableNode(*atomicContent))) {
+      NS_WARNING(
+          "AutoDeleteRangesHandler::GetAtomicContentToDelete() cannot find "
+          "removable atomic content");
+      return Err(NS_ERROR_FAILURE);
+    }
+    Result<CaretPoint, nsresult> caretPointOrError = HandleDeleteAtomicContent(
+        aHTMLEditor, *atomicContent, aWSRunScannerAtCaret.ScanStartRef(),
+        aWSRunScannerAtCaret, aEditingHost);
+    if (MOZ_UNLIKELY(caretPointOrError.isErr())) {
+      NS_WARNING("AutoDeleteRangesHandler::HandleDeleteAtomicContent() failed");
+      return caretPointOrError.propagateErr();
+    }
+    nsresult rv = caretPointOrError.unwrap().SuggestCaretPointTo(
+        aHTMLEditor, {SuggestCaret::OnlyIfHasSuggestion});
+    if (NS_FAILED(rv)) {
+      NS_WARNING("CaretPoint::SuggestCaretPointTo() failed");
+      return Err(rv);
+    }
+    NS_WARNING_ASSERTION(
+        rv != NS_SUCCESS_EDITOR_BUT_IGNORED_TRIVIAL_ERROR,
+        "CaretPoint::SuggestCaretPointTo() failed, but ignored");
+    return EditActionResult::HandledResult();
+  }
+
+  if (aScanFromCaretPointResult.ReachedOtherBlockElement()) {
+    if (NS_WARN_IF(!aScanFromCaretPointResult.GetContent()->IsElement())) {
+      return Err(NS_ERROR_FAILURE);
+    }
+    AutoBlockElementsJoiner joiner(*this);
+    if (!joiner.PrepareToDeleteAtOtherBlockBoundary(
+            aHTMLEditor, aDirectionAndAmount,
+            *aScanFromCaretPointResult.ElementPtr(),
+            aWSRunScannerAtCaret.ScanStartRef(), aWSRunScannerAtCaret)) {
+      return EditActionResult::CanceledResult();
+    }
+    Result<EditActionResult, nsresult> result = joiner.Run(
+        aHTMLEditor, aDirectionAndAmount, aStripWrappers,
+        aWSRunScannerAtCaret.ScanStartRef(), aRangesToDelete, aEditingHost);
+    NS_WARNING_ASSERTION(
+        result.isOk(),
+        "AutoBlockElementsJoiner::Run() failed (other block boundary)");
+    return result;
+  }
+
+  if (aScanFromCaretPointResult.ReachedCurrentBlockBoundary()) {
+    if (NS_WARN_IF(!aScanFromCaretPointResult.GetContent()->IsElement())) {
+      return Err(NS_ERROR_FAILURE);
+    }
+    AutoBlockElementsJoiner joiner(*this);
+    if (!joiner.PrepareToDeleteAtCurrentBlockBoundary(
+            aHTMLEditor, aDirectionAndAmount,
+            *aScanFromCaretPointResult.ElementPtr(),
+            aWSRunScannerAtCaret.ScanStartRef())) {
+      return EditActionResult::CanceledResult();
+    }
+    Result<EditActionResult, nsresult> result = joiner.Run(
+        aHTMLEditor, aDirectionAndAmount, aStripWrappers,
+        aWSRunScannerAtCaret.ScanStartRef(), aRangesToDelete, aEditingHost);
+    NS_WARNING_ASSERTION(
+        result.isOk(),
+        "AutoBlockElementsJoiner::Run() failed (current block boundary)");
+    return result;
+  }
+
+  MOZ_ASSERT_UNREACHABLE("New type of reached content hasn't been handled yet");
+  return EditActionResult::IgnoredResult();
+}
+
+nsresult HTMLEditor::AutoDeleteRangesHandler::
+    ComputeRangesToDeleteTextAroundCollapsedRanges(
+        nsIEditor::EDirection aDirectionAndAmount,
+        AutoRangeArray& aRangesToDelete, const Element& aEditingHost) const {
+  MOZ_ASSERT(aDirectionAndAmount == nsIEditor::eNext ||
+             aDirectionAndAmount == nsIEditor::ePrevious);
+
+  const auto caretPosition =
+      aRangesToDelete.GetFirstRangeStartPoint<EditorDOMPoint>();
+  MOZ_ASSERT(caretPosition.IsSetAndValid());
+  if (MOZ_UNLIKELY(NS_WARN_IF(!caretPosition.IsInContentNode()))) {
+    return NS_ERROR_FAILURE;
+  }
+
+  EditorDOMRangeInTexts rangeToDelete;
+  if (aDirectionAndAmount == nsIEditor::eNext) {
+    Result<EditorDOMRangeInTexts, nsresult> result =
+        WSRunScanner::GetRangeInTextNodesToForwardDeleteFrom(caretPosition,
+                                                             aEditingHost);
+    if (result.isErr()) {
+      NS_WARNING(
+          "WSRunScanner::GetRangeInTextNodesToForwardDeleteFrom() failed");
+      return result.unwrapErr();
+    }
+    rangeToDelete = result.unwrap();
+    if (!rangeToDelete.IsPositioned()) {
+      return NS_OK;  // no range to delete, but consume it.
+    }
+  } else {
+    Result<EditorDOMRangeInTexts, nsresult> result =
+        WSRunScanner::GetRangeInTextNodesToBackspaceFrom(caretPosition,
+                                                         aEditingHost);
+    if (result.isErr()) {
+      NS_WARNING("WSRunScanner::GetRangeInTextNodesToBackspaceFrom() failed");
+      return result.unwrapErr();
+    }
+    rangeToDelete = result.unwrap();
+    if (!rangeToDelete.IsPositioned()) {
+      return NS_OK;  // no range to delete, but consume it.
+    }
+  }
+
+  nsresult rv = aRangesToDelete.SetStartAndEnd(rangeToDelete.StartRef(),
+                                               rangeToDelete.EndRef());
+  NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                       "AutoArrayRanges::SetStartAndEnd() failed");
+  return rv;
+}
+
+Result<CaretPoint, nsresult>
+HTMLEditor::AutoDeleteRangesHandler::HandleDeleteTextAroundCollapsedRanges(
+    HTMLEditor& aHTMLEditor, nsIEditor::EDirection aDirectionAndAmount,
+    AutoRangeArray& aRangesToDelete, const Element& aEditingHost) {
+  MOZ_ASSERT(aHTMLEditor.IsEditActionDataAvailable());
+  MOZ_ASSERT(aDirectionAndAmount == nsIEditor::eNext ||
+             aDirectionAndAmount == nsIEditor::ePrevious);
+
+  nsresult rv = ComputeRangesToDeleteTextAroundCollapsedRanges(
+      aDirectionAndAmount, aRangesToDelete, aEditingHost);
+  if (NS_FAILED(rv)) {
+    return Err(NS_ERROR_FAILURE);
+  }
+  if (MOZ_UNLIKELY(aRangesToDelete.IsCollapsed())) {
+    return CaretPoint(EditorDOMPoint());  // no range to delete
+  }
+
+  // FYI: rangeToDelete does not contain newly empty inline ancestors which
+  //      are removed by DeleteTextAndNormalizeSurroundingWhiteSpaces().
+  //      So, if `getTargetRanges()` needs to include parent empty elements,
+  //      we need to extend the range with
+  //      HTMLEditUtils::GetMostDistantAncestorEditableEmptyInlineElement().
+  EditorRawDOMRange rangeToDelete(aRangesToDelete.FirstRangeRef());
+  if (MOZ_UNLIKELY(!rangeToDelete.IsInTextNodes())) {
+    NS_WARNING("The extended range to delete character was not in text nodes");
+    return Err(NS_ERROR_FAILURE);
+  }
+
+  Result<CaretPoint, nsresult> caretPointOrError =
+      aHTMLEditor.DeleteTextAndNormalizeSurroundingWhiteSpaces(
+          rangeToDelete.StartRef().AsInText(),
+          rangeToDelete.EndRef().AsInText(),
+          TreatEmptyTextNodes::RemoveAllEmptyInlineAncestors,
+          aDirectionAndAmount == nsIEditor::eNext ? DeleteDirection::Forward
+                                                  : DeleteDirection::Backward);
+  aHTMLEditor.TopLevelEditSubActionDataRef().mDidNormalizeWhitespaces = true;
+  NS_WARNING_ASSERTION(
+      caretPointOrError.isOk(),
+      "HTMLEditor::DeleteTextAndNormalizeSurroundingWhiteSpaces() failed");
+  return caretPointOrError;
+}
+
+Result<CaretPoint, nsresult> HTMLEditor::AutoDeleteRangesHandler::
+    HandleDeleteCollapsedSelectionAtWhiteSpaces(
+        HTMLEditor& aHTMLEditor, nsIEditor::EDirection aDirectionAndAmount,
+        const EditorDOMPoint& aPointToDelete, const Element& aEditingHost) {
+  MOZ_ASSERT(aHTMLEditor.IsEditActionDataAvailable());
+  MOZ_ASSERT(!StaticPrefs::editor_white_space_normalization_blink_compatible());
+
+  EditorDOMPoint pointToPutCaret;
+  if (aDirectionAndAmount == nsIEditor::eNext) {
+    Result<CaretPoint, nsresult> caretPointOrError =
+        WhiteSpaceVisibilityKeeper::DeleteInclusiveNextWhiteSpace(
+            aHTMLEditor, aPointToDelete, aEditingHost);
+    if (MOZ_UNLIKELY(caretPointOrError.isErr())) {
+      NS_WARNING(
+          "WhiteSpaceVisibilityKeeper::DeleteInclusiveNextWhiteSpace() failed");
+      return caretPointOrError;
+    }
+    caretPointOrError.unwrap().MoveCaretPointTo(
+        pointToPutCaret, aHTMLEditor,
+        {SuggestCaret::OnlyIfHasSuggestion,
+         SuggestCaret::OnlyIfTransactionsAllowedToDoIt});
+  } else {
+    Result<CaretPoint, nsresult> caretPointOrError =
+        WhiteSpaceVisibilityKeeper::DeletePreviousWhiteSpace(
+            aHTMLEditor, aPointToDelete, aEditingHost);
+    if (MOZ_UNLIKELY(caretPointOrError.isErr())) {
+      NS_WARNING(
+          "WhiteSpaceVisibilityKeeper::DeletePreviousWhiteSpace() failed");
+      return caretPointOrError;
+    }
+    caretPointOrError.unwrap().MoveCaretPointTo(
+        pointToPutCaret, aHTMLEditor,
+        {SuggestCaret::OnlyIfHasSuggestion,
+         SuggestCaret::OnlyIfTransactionsAllowedToDoIt});
+  }
+  const auto newCaretPosition =
+      aHTMLEditor.GetFirstSelectionStartPoint<EditorDOMPoint>();
+  if (MOZ_UNLIKELY(!newCaretPosition.IsSet())) {
+    NS_WARNING("There was no selection range");
+    return Err(NS_ERROR_EDITOR_UNEXPECTED_DOM_TREE);
+  }
+  Result<CaretPoint, nsresult> caretPointOrError =
+      aHTMLEditor.InsertBRElementIfHardLineIsEmptyAndEndsWithBlockBoundary(
+          newCaretPosition);
+  if (MOZ_UNLIKELY(caretPointOrError.isErr())) {
+    NS_WARNING(
+        "HTMLEditor::InsertBRElementIfHardLineIsEmptyAndEndsWithBlockBoundary()"
+        " failed");
+    return caretPointOrError;
+  }
+  caretPointOrError.unwrap().MoveCaretPointTo(
+      pointToPutCaret, {SuggestCaret::OnlyIfHasSuggestion});
+  return CaretPoint(std::move(pointToPutCaret));
+}
+
+Result<CaretPoint, nsresult> HTMLEditor::AutoDeleteRangesHandler::
+    HandleDeleteCollapsedSelectionAtVisibleChar(
+        HTMLEditor& aHTMLEditor, nsIEditor::EDirection aDirectionAndAmount,
+        AutoRangeArray& aRangesToDelete,
+        const EditorDOMPoint& aPointAtDeletingChar,
+        const Element& aEditingHost) {
+  MOZ_ASSERT(aHTMLEditor.IsTopLevelEditSubActionDataAvailable());
+  MOZ_ASSERT(!StaticPrefs::editor_white_space_normalization_blink_compatible());
+  MOZ_ASSERT(aPointAtDeletingChar.IsSet());
+  MOZ_ASSERT(aPointAtDeletingChar.IsInTextNode());
+
+  OwningNonNull<Text> visibleTextNode =
+      *aPointAtDeletingChar.ContainerAs<Text>();
+  EditorDOMPoint startToDelete, endToDelete;
+  // FIXME: This does not care grapheme cluster of complicate character
+  // sequence like Emoji.
+  // TODO: Investigate what happens if a grapheme cluster which should be
+  // delete once is split to multiple text nodes.
+  // TODO: We should stop using this path, instead, we should extend the range
+  // before calling this method.
+  if (aDirectionAndAmount == nsIEditor::ePrevious) {
+    if (MOZ_UNLIKELY(aPointAtDeletingChar.IsStartOfContainer())) {
+      return Err(NS_ERROR_UNEXPECTED);
+    }
+    startToDelete = aPointAtDeletingChar.PreviousPoint();
+    endToDelete = aPointAtDeletingChar;
+    // Bug 1068979: delete both codepoints if surrogate pair
+    if (!startToDelete.IsStartOfContainer()) {
+      const nsTextFragment* text = &visibleTextNode->TextFragment();
+      if (text->IsLowSurrogateFollowingHighSurrogateAt(
+              startToDelete.Offset())) {
+        startToDelete.RewindOffset();
+      }
+    }
+  } else {
+    if (NS_WARN_IF(aRangesToDelete.Ranges().IsEmpty()) ||
+        NS_WARN_IF(aRangesToDelete.FirstRangeRef()->GetStartContainer() !=
+                   aPointAtDeletingChar.GetContainer()) ||
+        NS_WARN_IF(aRangesToDelete.FirstRangeRef()->GetEndContainer() !=
+                   aPointAtDeletingChar.GetContainer())) {
+      return Err(NS_ERROR_FAILURE);
+    }
+    startToDelete = aRangesToDelete.FirstRangeRef()->StartRef();
+    endToDelete = aRangesToDelete.FirstRangeRef()->EndRef();
+  }
+
+  {
+    Result<CaretPoint, nsresult> caretPointOrError =
+        WhiteSpaceVisibilityKeeper::PrepareToDeleteRangeAndTrackPoints(
+            aHTMLEditor, &startToDelete, &endToDelete, aEditingHost);
+    if (MOZ_UNLIKELY(caretPointOrError.isErr())) {
+      NS_WARNING(
+          "WhiteSpaceVisibilityKeeper::PrepareToDeleteRangeAndTrackPoints() "
+          "failed");
+      return caretPointOrError.propagateErr();
+    }
+    // Ignore caret position because we'll set caret position below
+    caretPointOrError.unwrap().IgnoreCaretPointSuggestion();
+  }
+
+  if (aHTMLEditor.MayHaveMutationEventListeners(
+          NS_EVENT_BITS_MUTATION_NODEREMOVED |
+          NS_EVENT_BITS_MUTATION_NODEREMOVEDFROMDOCUMENT |
+          NS_EVENT_BITS_MUTATION_ATTRMODIFIED |
+          NS_EVENT_BITS_MUTATION_CHARACTERDATAMODIFIED) &&
+      (NS_WARN_IF(!startToDelete.IsSetAndValid()) ||
+       NS_WARN_IF(!startToDelete.IsInTextNode()) ||
+       NS_WARN_IF(!endToDelete.IsSetAndValid()) ||
+       NS_WARN_IF(!endToDelete.IsInTextNode()) ||
+       NS_WARN_IF(startToDelete.ContainerAs<Text>() != visibleTextNode) ||
+       NS_WARN_IF(endToDelete.ContainerAs<Text>() != visibleTextNode) ||
+       NS_WARN_IF(startToDelete.Offset() >= endToDelete.Offset()))) {
+    NS_WARNING("Mutation event listener changed the DOM tree");
+    return Err(NS_ERROR_EDITOR_UNEXPECTED_DOM_TREE);
+  }
+
+  EditorDOMPoint pointToPutCaret = startToDelete;
+  {
+    AutoTrackDOMPoint trackPointToPutCaret(aHTMLEditor.RangeUpdaterRef(),
+                                           &pointToPutCaret);
+    Result<CaretPoint, nsresult> caretPointOrError =
+        aHTMLEditor.DeleteTextWithTransaction(
+            visibleTextNode, startToDelete.Offset(),
+            endToDelete.Offset() - startToDelete.Offset());
+    if (MOZ_UNLIKELY(caretPointOrError.isErr())) {
+      NS_WARNING("HTMLEditor::DeleteTextWithTransaction() failed");
+      return caretPointOrError.propagateErr();
+    }
+    trackPointToPutCaret.FlushAndStopTracking();
+    caretPointOrError.unwrap().MoveCaretPointTo(
+        pointToPutCaret, aHTMLEditor,
+        {SuggestCaret::OnlyIfHasSuggestion,
+         SuggestCaret::OnlyIfTransactionsAllowedToDoIt});
+  }
+
+  // XXX When Backspace key is pressed, Chromium removes following empty
+  //     text nodes when removing the last character of the non-empty text
+  //     node.  However, Edge never removes empty text nodes even if
+  //     selection is in the following empty text node(s).  For now, we
+  //     should keep our traditional behavior same as Edge for backward
+  //     compatibility.
+  // XXX When Delete key is pressed, Edge removes all preceding empty
+  //     text nodes when removing the first character of the non-empty
+  //     text node.  Chromium removes only selected empty text node and
+  //     following empty text nodes and the first character of the
+  //     non-empty text node.  For now, we should keep our traditional
+  //     behavior same as Chromium for backward compatibility.
+  {
+    AutoTrackDOMPoint trackPointToPutCaret(aHTMLEditor.RangeUpdaterRef(),
+                                           &pointToPutCaret);
+    nsresult rv =
+        DeleteNodeIfInvisibleAndEditableTextNode(aHTMLEditor, visibleTextNode);
+    if (NS_WARN_IF(rv == NS_ERROR_EDITOR_DESTROYED)) {
+      return Err(NS_ERROR_EDITOR_DESTROYED);
+    }
+    NS_WARNING_ASSERTION(
+        NS_SUCCEEDED(rv),
+        "AutoDeleteRangesHandler::DeleteNodeIfInvisibleAndEditableTextNode() "
+        "failed, but ignored");
+  }
+
+  if (NS_WARN_IF(!pointToPutCaret.IsSet())) {
+    return Err(NS_ERROR_EDITOR_UNEXPECTED_DOM_TREE);
+  }
+
+  // XXX `Selection` may be modified by mutation event listeners so
+  //     that we should use EditorDOMPoint::AtEndOf(visibleTextNode)
+  //     instead.  (Perhaps, we don't and/or shouldn't need to do this
+  //     if the text node is preformatted.)
+  AutoTrackDOMPoint trackPointToPutCaret(aHTMLEditor.RangeUpdaterRef(),
+                                         &pointToPutCaret);
+  Result<CaretPoint, nsresult> caretPointOrError =
+      aHTMLEditor.InsertBRElementIfHardLineIsEmptyAndEndsWithBlockBoundary(
+          pointToPutCaret);
+  if (MOZ_UNLIKELY(caretPointOrError.isErr())) {
+    NS_WARNING(
+        "HTMLEditor::InsertBRElementIfHardLineIsEmptyAndEndsWithBlockBoundary()"
+        " failed");
+    return caretPointOrError.propagateErr();
+  }
+  trackPointToPutCaret.FlushAndStopTracking();
+  caretPointOrError.unwrap().MoveCaretPointTo(
+      pointToPutCaret, {SuggestCaret::OnlyIfHasSuggestion});
+  // Remember that we did a ranged delete for the benefit of
+  // AfterEditInner().
+  aHTMLEditor.TopLevelEditSubActionDataRef().mDidDeleteNonCollapsedRange = true;
+  return CaretPoint(std::move(pointToPutCaret));
+}
+
+// static
+nsIContent* HTMLEditor::AutoDeleteRangesHandler::GetAtomicContentToDelete(
+    nsIEditor::EDirection aDirectionAndAmount,
+    const WSRunScanner& aWSRunScannerAtCaret,
+    const WSScanResult& aScanFromCaretPointResult) {
+  MOZ_ASSERT(aScanFromCaretPointResult.GetContent());
+
+  if (!aScanFromCaretPointResult.ReachedSpecialContent()) {
+    return aScanFromCaretPointResult.GetContent();
+  }
+
+  if (!aScanFromCaretPointResult.GetContent()->IsText() ||
+      HTMLEditUtils::IsRemovableNode(*aScanFromCaretPointResult.GetContent())) {
+    return aScanFromCaretPointResult.GetContent();
+  }
+
+  // aScanFromCaretPointResult is non-removable text node.
+  // Since we try removing atomic content, we look for removable node from
+  // scanned point that is non-removable text.
+  nsIContent* removableRoot = aScanFromCaretPointResult.GetContent();
+  while (removableRoot && !HTMLEditUtils::IsRemovableNode(*removableRoot)) {
+    removableRoot = removableRoot->GetParent();
+  }
+
+  if (removableRoot) {
+    return removableRoot;
+  }
+
+  // Not found better content. This content may not be removable.
+  return aScanFromCaretPointResult.GetContent();
+}
+
+nsresult
+HTMLEditor::AutoDeleteRangesHandler::ComputeRangesToDeleteAtomicContent(
+    Element* aEditingHost, const nsIContent& aAtomicContent,
+    AutoRangeArray& aRangesToDelete) const {
+  EditorDOMRange rangeToDelete =
+      WSRunScanner::GetRangesForDeletingAtomicContent(aEditingHost,
+                                                      aAtomicContent);
+  if (!rangeToDelete.IsPositioned()) {
+    NS_WARNING("WSRunScanner::GetRangeForDeleteAContentNode() failed");
+    return NS_ERROR_FAILURE;
+  }
+  nsresult rv = aRangesToDelete.SetStartAndEnd(rangeToDelete.StartRef(),
+                                               rangeToDelete.EndRef());
+  NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                       "AutoRangeArray::SetStartAndEnd() failed");
+  return rv;
+}
+
+Result<CaretPoint, nsresult>
+HTMLEditor::AutoDeleteRangesHandler::HandleDeleteAtomicContent(
+    HTMLEditor& aHTMLEditor, nsIContent& aAtomicContent,
+    const EditorDOMPoint& aCaretPoint, const WSRunScanner& aWSRunScannerAtCaret,
+    const Element& aEditingHost) {
+  MOZ_ASSERT(aHTMLEditor.IsEditActionDataAvailable());
+  MOZ_ASSERT(!HTMLEditUtils::IsInvisibleBRElement(aAtomicContent));
+  MOZ_ASSERT(&aAtomicContent != aWSRunScannerAtCaret.GetEditingHost());
+
+  EditorDOMPoint pointToPutCaret = aCaretPoint;
+  {
+    AutoTrackDOMPoint trackPointToPutCaret(aHTMLEditor.RangeUpdaterRef(),
+                                           &pointToPutCaret);
+    Result<CaretPoint, nsresult> caretPointOrError =
+        WhiteSpaceVisibilityKeeper::DeleteContentNodeAndJoinTextNodesAroundIt(
+            aHTMLEditor, aAtomicContent, aCaretPoint, aEditingHost);
+    if (MOZ_UNLIKELY(caretPointOrError.isErr())) {
+      NS_WARNING(
+          "WhiteSpaceVisibilityKeeper::"
+          "DeleteContentNodeAndJoinTextNodesAroundIt() failed");
+      return caretPointOrError;
+    }
+    trackPointToPutCaret.FlushAndStopTracking();
+    caretPointOrError.unwrap().MoveCaretPointTo(
+        pointToPutCaret, aHTMLEditor,
+        {SuggestCaret::OnlyIfHasSuggestion,
+         SuggestCaret::OnlyIfTransactionsAllowedToDoIt});
+    if (NS_WARN_IF(!pointToPutCaret.IsSet())) {
+      return Err(NS_ERROR_EDITOR_UNEXPECTED_DOM_TREE);
+    }
+  }
+
+  {
+    AutoTrackDOMPoint trackPointToPutCaret(aHTMLEditor.RangeUpdaterRef(),
+                                           &pointToPutCaret);
+    Result<CaretPoint, nsresult> caretPointOrError =
+        aHTMLEditor.InsertBRElementIfHardLineIsEmptyAndEndsWithBlockBoundary(
+            pointToPutCaret);
+    if (MOZ_UNLIKELY(caretPointOrError.isErr())) {
+      NS_WARNING(
+          "HTMLEditor::"
+          "InsertBRElementIfHardLineIsEmptyAndEndsWithBlockBoundary()"
+          " failed");
+      return caretPointOrError;
+    }
+    trackPointToPutCaret.FlushAndStopTracking();
+    caretPointOrError.unwrap().MoveCaretPointTo(
+        pointToPutCaret, aHTMLEditor, {SuggestCaret::OnlyIfHasSuggestion});
+    if (NS_WARN_IF(!pointToPutCaret.IsSet())) {
+      return Err(NS_ERROR_EDITOR_UNEXPECTED_DOM_TREE);
+    }
+  }
+  return CaretPoint(std::move(pointToPutCaret));
+}
+
+bool HTMLEditor::AutoDeleteRangesHandler::AutoBlockElementsJoiner::
+    PrepareToDeleteAtOtherBlockBoundary(
+        const HTMLEditor& aHTMLEditor,
+        nsIEditor::EDirection aDirectionAndAmount, Element& aOtherBlockElement,
+        const EditorDOMPoint& aCaretPoint,
+        const WSRunScanner& aWSRunScannerAtCaret) {
+  MOZ_ASSERT(aHTMLEditor.IsEditActionDataAvailable());
+  MOZ_ASSERT(aCaretPoint.IsSetAndValid());
+
+  mMode = Mode::JoinOtherBlock;
+
+  // Make sure it's not a table element.  If so, cancel the operation
+  // (translation: users cannot backspace or delete across table cells)
+  if (HTMLEditUtils::IsAnyTableElement(&aOtherBlockElement)) {
+    return false;
+  }
+
+  // First find the adjacent node in the block
+  if (aDirectionAndAmount == nsIEditor::ePrevious) {
+    mLeafContentInOtherBlock = HTMLEditUtils::GetLastLeafContent(
+        aOtherBlockElement, {LeafNodeType::OnlyEditableLeafNode},
+        &aOtherBlockElement);
+    mLeftContent = mLeafContentInOtherBlock;
+    mRightContent = aCaretPoint.GetContainerAs<nsIContent>();
+  } else {
+    mLeafContentInOtherBlock = HTMLEditUtils::GetFirstLeafContent(
+        aOtherBlockElement, {LeafNodeType::OnlyEditableLeafNode},
+        &aOtherBlockElement);
+    mLeftContent = aCaretPoint.GetContainerAs<nsIContent>();
+    mRightContent = mLeafContentInOtherBlock;
+  }
+
+  // Next to a block.  See if we are between the block and a `<br>`.
+  // If so, we really want to delete the `<br>`.  Else join content at
+  // selection to the block.
+  WSScanResult scanFromCaretResult =
+      aDirectionAndAmount == nsIEditor::eNext
+          ? aWSRunScannerAtCaret.ScanPreviousVisibleNodeOrBlockBoundaryFrom(
+                aCaretPoint)
+          : aWSRunScannerAtCaret.ScanNextVisibleNodeOrBlockBoundaryFrom(
+                aCaretPoint);
+  // If we found a `<br>` element, we need to delete it instead of joining the
+  // contents.
+  if (scanFromCaretResult.ReachedBRElement()) {
+    mBRElement = scanFromCaretResult.BRElementPtr();
+    mMode = Mode::DeleteBRElement;
+    return true;
+  }
+
+  return mLeftContent && mRightContent;
+}
+
+nsresult HTMLEditor::AutoDeleteRangesHandler::AutoBlockElementsJoiner::
+    ComputeRangesToDeleteBRElement(AutoRangeArray& aRangesToDelete) const {
+  MOZ_ASSERT(mBRElement);
+  // XXX Why don't we scan invisible leading white-spaces which follows the
+  //     `<br>` element?
+  nsresult rv = aRangesToDelete.SelectNode(*mBRElement);
+  NS_WARNING_ASSERTION(NS_SUCCEEDED(rv), "AutoRangeArray::SelectNode() failed");
+  return rv;
+}
+
+Result<EditActionResult, nsresult>
+HTMLEditor::AutoDeleteRangesHandler::AutoBlockElementsJoiner::DeleteBRElement(
+    HTMLEditor& aHTMLEditor, nsIEditor::EDirection aDirectionAndAmount,
+    const Element& aEditingHost) {
+  MOZ_ASSERT(aHTMLEditor.IsEditActionDataAvailable());
+  MOZ_ASSERT(mBRElement);
+
+  // If we're deleting selection (not replacing with new content), we should
+  // put caret to end of preceding text node if there is.  Then, users can type
+  // text in it like the other browsers.
+  EditorDOMPoint pointToPutCaret = [&]() {
+    if (!MayEditActionDeleteAroundCollapsedSelection(
+            aHTMLEditor.GetEditAction())) {
+      return EditorDOMPoint();
+    }
+    WSRunScanner scanner(&aEditingHost, EditorRawDOMPoint(mBRElement));
+    WSScanResult maybePreviousText =
+        scanner.ScanPreviousVisibleNodeOrBlockBoundaryFrom(
+            EditorRawDOMPoint(mBRElement));
+    if (maybePreviousText.IsContentEditable() &&
+        maybePreviousText.InVisibleOrCollapsibleCharacters() &&
+        !HTMLEditor::GetLinkElement(maybePreviousText.TextPtr())) {
+      return maybePreviousText.Point<EditorDOMPoint>();
+    }
+    WSScanResult maybeNextText = scanner.ScanNextVisibleNodeOrBlockBoundaryFrom(
+        EditorRawDOMPoint::After(*mBRElement));
+    if (maybeNextText.IsContentEditable() &&
+        maybeNextText.InVisibleOrCollapsibleCharacters()) {
+      return maybeNextText.Point<EditorDOMPoint>();
+    }
+    return EditorDOMPoint();
+  }();
+
+  // If we found a `<br>` element, we should delete it instead of joining the
+  // contents.
+  nsresult rv =
+      aHTMLEditor.DeleteNodeWithTransaction(MOZ_KnownLive(*mBRElement));
+  if (NS_FAILED(rv)) {
+    NS_WARNING("EditorBase::DeleteNodeWithTransaction() failed");
+    return Err(rv);
+  }
+
+  if (mLeftContent && mRightContent &&
+      HTMLEditUtils::GetInclusiveAncestorAnyTableElement(*mLeftContent) !=
+          HTMLEditUtils::GetInclusiveAncestorAnyTableElement(*mRightContent)) {
+    return EditActionResult::HandledResult();
+  }
+
+  // Put selection at edge of block and we are done.
+  if (NS_WARN_IF(!mLeafContentInOtherBlock)) {
+    // XXX This must be odd case.  The other block can be empty.
+    return Err(NS_ERROR_FAILURE);
+  }
+
+  if (pointToPutCaret.IsSet()) {
+    nsresult rv = aHTMLEditor.CollapseSelectionTo(pointToPutCaret);
+    if (NS_WARN_IF(rv == NS_ERROR_EDITOR_DESTROYED)) {
+      return Err(NS_ERROR_EDITOR_DESTROYED);
+    }
+    if (NS_SUCCEEDED(rv)) {
+      // If we prefer to use style in the previous line, we should forget
+      // previous styles since the caret position has all styles which we want
+      // to use with new content.
+      if (nsIEditor::DirectionIsBackspace(aDirectionAndAmount)) {
+        aHTMLEditor.TopLevelEditSubActionDataRef()
+            .mCachedPendingStyles->Clear();
+      }
+      // And we don't want to keep extending a link at ex-end of the previous
+      // paragraph.
+      if (HTMLEditor::GetLinkElement(pointToPutCaret.GetContainer())) {
+        aHTMLEditor.mPendingStylesToApplyToNewContent
+            ->ClearLinkAndItsSpecifiedStyle();
+      }
+    } else {
+      NS_WARNING("EditorBase::CollapseSelectionTo() failed, but ignored");
+    }
+    return EditActionResult::HandledResult();
+  }
+
+  EditorRawDOMPoint newCaretPosition =
+      HTMLEditUtils::GetGoodCaretPointFor<EditorRawDOMPoint>(
+          *mLeafContentInOtherBlock, aDirectionAndAmount);
+  if (MOZ_UNLIKELY(!newCaretPosition.IsSet())) {
+    NS_WARNING("HTMLEditUtils::GetGoodCaretPointFor() failed");
+    return Err(NS_ERROR_FAILURE);
+  }
+  rv = aHTMLEditor.CollapseSelectionTo(newCaretPosition);
+  if (NS_WARN_IF(rv == NS_ERROR_EDITOR_DESTROYED)) {
+    return Err(NS_ERROR_EDITOR_DESTROYED);
+  }
+  NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                       "EditorBase::CollapseSelectionTo() failed, but ignored");
+  return EditActionResult::HandledResult();
+}
+
+nsresult HTMLEditor::AutoDeleteRangesHandler::AutoBlockElementsJoiner::
+    ComputeRangesToDeleteAtOtherBlockBoundary(
+        const HTMLEditor& aHTMLEditor,
+        nsIEditor::EDirection aDirectionAndAmount,
+        const EditorDOMPoint& aCaretPoint, AutoRangeArray& aRangesToDelete,
+        const Element& aEditingHost) const {
+  MOZ_ASSERT(aHTMLEditor.IsEditActionDataAvailable());
+  MOZ_ASSERT(aCaretPoint.IsSetAndValid());
+  MOZ_ASSERT(mLeftContent);
+  MOZ_ASSERT(mRightContent);
+
+  if (HTMLEditUtils::GetInclusiveAncestorAnyTableElement(*mLeftContent) !=
+      HTMLEditUtils::GetInclusiveAncestorAnyTableElement(*mRightContent)) {
+    if (!mDeleteRangesHandlerConst.CanFallbackToDeleteRangesWithTransaction(
+            aRangesToDelete)) {
+      nsresult rv = aRangesToDelete.Collapse(aCaretPoint);
+      NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                           "AutoRangeArray::Collapse() failed");
+      return rv;
+    }
+    nsresult rv = mDeleteRangesHandlerConst
+                      .FallbackToComputeRangesToDeleteRangesWithTransaction(
+                          aHTMLEditor, aRangesToDelete);
+    NS_WARNING_ASSERTION(
+        NS_SUCCEEDED(rv),
+        "AutoDeleteRangesHandler::"
+        "FallbackToComputeRangesToDeleteRangesWithTransaction() failed");
+    return rv;
+  }
+
+  AutoInclusiveAncestorBlockElementsJoiner joiner(*mLeftContent,
+                                                  *mRightContent);
+  Result<bool, nsresult> canJoinThem =
+      joiner.Prepare(aHTMLEditor, aEditingHost);
+  if (canJoinThem.isErr()) {
+    NS_WARNING("AutoInclusiveAncestorBlockElementsJoiner::Prepare() failed");
+    return canJoinThem.unwrapErr();
+  }
+  if (canJoinThem.inspect() && joiner.CanJoinBlocks() &&
+      !joiner.ShouldDeleteLeafContentInstead()) {
+    nsresult rv =
+        joiner.ComputeRangesToDelete(aHTMLEditor, aCaretPoint, aRangesToDelete);
+    NS_WARNING_ASSERTION(
+        NS_SUCCEEDED(rv),
+        "AutoInclusiveAncestorBlockElementsJoiner::ComputeRangesToDelete() "
+        "failed");
+    return rv;
+  }
+
+  // If AutoInclusiveAncestorBlockElementsJoiner didn't handle it and it's not
+  // canceled, user may want to modify the start leaf node or the last leaf
+  // node of the block.
+  if (mLeafContentInOtherBlock == aCaretPoint.GetContainer()) {
+    return NS_OK;
+  }
+
+  AutoHideSelectionChanges hideSelectionChanges(aHTMLEditor.SelectionRef());
+
+  // If it's ignored, it didn't modify the DOM tree.  In this case, user must
+  // want to delete nearest leaf node in the other block element.
+  // TODO: We need to consider this before calling ComputeRangesToDelete() for
+  //       computing the deleting range.
+  EditorRawDOMPoint newCaretPoint =
+      aDirectionAndAmount == nsIEditor::ePrevious
+          ? EditorRawDOMPoint::AtEndOf(*mLeafContentInOtherBlock)
+          : EditorRawDOMPoint(mLeafContentInOtherBlock, 0);
+  // If new caret position is same as current caret position, we can do
+  // nothing anymore.
+  if (aRangesToDelete.IsCollapsed() &&
+      aRangesToDelete.FocusRef() == newCaretPoint.ToRawRangeBoundary()) {
+    return NS_OK;
+  }
+  // TODO: Stop modifying the `Selection` for computing the targer ranges.
+  nsresult rv = aHTMLEditor.CollapseSelectionTo(newCaretPoint);
+  if (MOZ_UNLIKELY(rv == NS_ERROR_EDITOR_DESTROYED)) {
+    NS_WARNING(
+        "EditorBase::CollapseSelectionTo() caused destroying the editor");
+    return NS_ERROR_EDITOR_DESTROYED;
+  }
+  NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                       "EditorBase::CollapseSelectionTo() failed");
+  if (NS_SUCCEEDED(rv)) {
+    aRangesToDelete.Initialize(aHTMLEditor.SelectionRef());
+    AutoDeleteRangesHandler anotherHandler(mDeleteRangesHandlerConst);
+    rv = anotherHandler.ComputeRangesToDelete(aHTMLEditor, aDirectionAndAmount,
+                                              aRangesToDelete, aEditingHost);
+    NS_WARNING_ASSERTION(
+        NS_SUCCEEDED(rv),
+        "Recursive AutoDeleteRangesHandler::ComputeRangesToDelete() failed");
+  }
+  // Restore selection.
+  nsresult rvCollapsingSelectionTo =
+      aHTMLEditor.CollapseSelectionTo(aCaretPoint);
+  if (MOZ_UNLIKELY(rvCollapsingSelectionTo == NS_ERROR_EDITOR_DESTROYED)) {
+    NS_WARNING(
+        "EditorBase::CollapseSelectionTo() caused destroying the editor");
+    return NS_ERROR_EDITOR_DESTROYED;
+  }
+  NS_WARNING_ASSERTION(
+      NS_SUCCEEDED(rvCollapsingSelectionTo),
+      "EditorBase::CollapseSelectionTo() failed to restore caret position");
+  return NS_SUCCEEDED(rv) && NS_SUCCEEDED(rvCollapsingSelectionTo)
+             ? NS_OK
+             : NS_ERROR_FAILURE;
+}
+
+Result<EditActionResult, nsresult> HTMLEditor::AutoDeleteRangesHandler::
+    AutoBlockElementsJoiner::HandleDeleteAtOtherBlockBoundary(
+        HTMLEditor& aHTMLEditor, nsIEditor::EDirection aDirectionAndAmount,
+        nsIEditor::EStripWrappers aStripWrappers,
+        const EditorDOMPoint& aCaretPoint, AutoRangeArray& aRangesToDelete,
+        const Element& aEditingHost) {
+  MOZ_ASSERT(aHTMLEditor.IsEditActionDataAvailable());
+  MOZ_ASSERT(aCaretPoint.IsSetAndValid());
+  MOZ_ASSERT(mDeleteRangesHandler);
+  MOZ_ASSERT(mLeftContent);
+  MOZ_ASSERT(mRightContent);
+
+  if (HTMLEditUtils::GetInclusiveAncestorAnyTableElement(*mLeftContent) !=
+      HTMLEditUtils::GetInclusiveAncestorAnyTableElement(*mRightContent)) {
+    // If we have not deleted `<br>` element and are not called recursively,
+    // we should call `DeleteRangesWithTransaction()` here.
+    if (!mDeleteRangesHandler->CanFallbackToDeleteRangesWithTransaction(
+            aRangesToDelete)) {
+      return EditActionResult::IgnoredResult();
+    }
+    Result<CaretPoint, nsresult> caretPointOrError =
+        mDeleteRangesHandler->FallbackToDeleteRangesWithTransaction(
+            aHTMLEditor, aRangesToDelete);
+    if (MOZ_UNLIKELY(caretPointOrError.isErr())) {
+      NS_WARNING(
+          "AutoDeleteRangesHandler::FallbackToDeleteRangesWithTransaction() "
+          "failed");
+      return caretPointOrError.propagateErr();
+    }
+    nsresult rv = caretPointOrError.inspect().SuggestCaretPointTo(
+        aHTMLEditor, {SuggestCaret::OnlyIfHasSuggestion,
+                      SuggestCaret::OnlyIfTransactionsAllowedToDoIt,
+                      SuggestCaret::AndIgnoreTrivialError});
+    if (NS_FAILED(rv)) {
+      NS_WARNING("CaretPoint::SuggestCaretPointTo() failed");
+      return Err(rv);
+    }
+    NS_WARNING_ASSERTION(
+        rv != NS_SUCCESS_EDITOR_BUT_IGNORED_TRIVIAL_ERROR,
+        "CaretPoint::SuggestCaretPointTo() failed, but ignored");
+    // Don't return "ignored" to avoid to fall it back to delete ranges
+    // recursively.
+    return EditActionResult::HandledResult();
+  }
+
+  // Else we are joining content to block
+  AutoInclusiveAncestorBlockElementsJoiner joiner(*mLeftContent,
+                                                  *mRightContent);
+  Result<bool, nsresult> canJoinThem =
+      joiner.Prepare(aHTMLEditor, aEditingHost);
+  if (MOZ_UNLIKELY(canJoinThem.isErr())) {
+    NS_WARNING("AutoInclusiveAncestorBlockElementsJoiner::Prepare() failed");
+    return canJoinThem.propagateErr();
+  }
+
+  if (!canJoinThem.inspect()) {
+    nsresult rv = aHTMLEditor.CollapseSelectionTo(aCaretPoint);
+    if (NS_WARN_IF(rv == NS_ERROR_EDITOR_DESTROYED)) {
+      return Err(NS_ERROR_EDITOR_DESTROYED);
+    }
+    NS_WARNING_ASSERTION(
+        NS_SUCCEEDED(rv),
+        "EditorBase::CollapseSelectionTo() failed, but ignored");
+    return EditActionResult::CanceledResult();
+  }
+
+  auto result = EditActionResult::IgnoredResult();
+  EditorDOMPoint pointToPutCaret(aCaretPoint);
+  if (joiner.CanJoinBlocks()) {
+    {
+      AutoTrackDOMPoint tracker(aHTMLEditor.RangeUpdaterRef(),
+                                &pointToPutCaret);
+      Result<EditActionResult, nsresult> joinResult =
+          joiner.Run(aHTMLEditor, aEditingHost);
+      if (MOZ_UNLIKELY(joinResult.isErr())) {
+        NS_WARNING("AutoInclusiveAncestorBlockElementsJoiner::Run() failed");
+        return joinResult;
+      }
+      result |= joinResult.unwrap();
+#ifdef DEBUG
+      if (joiner.ShouldDeleteLeafContentInstead()) {
+        NS_ASSERTION(
+            result.Ignored(),
+            "Assumed `AutoInclusiveAncestorBlockElementsJoiner::Run()` "
+            "returning ignored, but returned not ignored");
+      } else {
+        NS_ASSERTION(
+            !result.Ignored(),
+            "Assumed `AutoInclusiveAncestorBlockElementsJoiner::Run()` "
+            "returning handled, but returned ignored");
+      }
+#endif  // #ifdef DEBUG
+      // If we're deleting selection (not replacing with new content) and
+      // AutoInclusiveAncestorBlockElementsJoiner computed new caret position,
+      // we should use it.  Otherwise, we should keep the our traditional
+      // behavior.
+      if (result.Handled() && joiner.PointRefToPutCaret().IsSet()) {
+        nsresult rv =
+            aHTMLEditor.CollapseSelectionTo(joiner.PointRefToPutCaret());
+        if (NS_WARN_IF(rv == NS_ERROR_EDITOR_DESTROYED)) {
+          return Err(NS_ERROR_EDITOR_DESTROYED);
+        }
+        if (NS_FAILED(rv)) {
+          NS_WARNING("EditorBase::CollapseSelectionTo() failed, but ignored");
+          return result;
+        }
+        // If we prefer to use style in the previous line, we should forget
+        // previous styles since the caret position has all styles which we want
+        // to use with new content.
+        if (nsIEditor::DirectionIsBackspace(aDirectionAndAmount)) {
+          aHTMLEditor.TopLevelEditSubActionDataRef()
+              .mCachedPendingStyles->Clear();
+        }
+        // And we don't want to keep extending a link at ex-end of the previous
+        // paragraph.
+        if (HTMLEditor::GetLinkElement(
+                joiner.PointRefToPutCaret().GetContainer())) {
+          aHTMLEditor.mPendingStylesToApplyToNewContent
+              ->ClearLinkAndItsSpecifiedStyle();
+        }
+        return result;
+      }
+    }
+
+    // If AutoInclusiveAncestorBlockElementsJoiner didn't handle it and it's not
+    // canceled, user may want to modify the start leaf node or the last leaf
+    // node of the block.
+    if (result.Ignored() &&
+        mLeafContentInOtherBlock != aCaretPoint.GetContainer()) {
+      // If it's ignored, it didn't modify the DOM tree.  In this case, user
+      // must want to delete nearest leaf node in the other block element.
+      // TODO: We need to consider this before calling Run() for computing the
+      //       deleting range.
+      EditorRawDOMPoint newCaretPoint =
+          aDirectionAndAmount == nsIEditor::ePrevious
+              ? EditorRawDOMPoint::AtEndOf(*mLeafContentInOtherBlock)
+              : EditorRawDOMPoint(mLeafContentInOtherBlock, 0);
+      // If new caret position is same as current caret position, we can do
+      // nothing anymore.
+      if (aRangesToDelete.IsCollapsed() &&
+          aRangesToDelete.FocusRef() == newCaretPoint.ToRawRangeBoundary()) {
+        return EditActionResult::CanceledResult();
+      }
+      nsresult rv = aHTMLEditor.CollapseSelectionTo(newCaretPoint);
+      if (NS_FAILED(rv)) {
+        NS_WARNING("EditorBase::CollapseSelectionTo() failed");
+        return Err(rv);
+      }
+      AutoRangeArray rangesToDelete(aHTMLEditor.SelectionRef());
+      AutoDeleteRangesHandler anotherHandler(mDeleteRangesHandler);
+      Result<EditActionResult, nsresult> fallbackResult =
+          anotherHandler.Run(aHTMLEditor, aDirectionAndAmount, aStripWrappers,
+                             rangesToDelete, aEditingHost);
+      if (MOZ_UNLIKELY(fallbackResult.isErr())) {
+        NS_WARNING("Recursive AutoDeleteRangesHandler::Run() failed");
+        return fallbackResult;
+      }
+      result |= fallbackResult.unwrap();
+      return result;
+    }
+  } else {
+    result.MarkAsHandled();
+  }
+
+  // Otherwise, we must have deleted the selection as user expected.
+  nsresult rv = aHTMLEditor.CollapseSelectionTo(pointToPutCaret);
+  if (NS_WARN_IF(rv == NS_ERROR_EDITOR_DESTROYED)) {
+    return Err(NS_ERROR_EDITOR_DESTROYED);
+  }
+  NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                       "EditorBase::CollapseSelectionTo() failed, but ignored");
+  return result;
+}
+
+bool HTMLEditor::AutoDeleteRangesHandler::AutoBlockElementsJoiner::
+    PrepareToDeleteAtCurrentBlockBoundary(
+        const HTMLEditor& aHTMLEditor,
+        nsIEditor::EDirection aDirectionAndAmount,
+        Element& aCurrentBlockElement, const EditorDOMPoint& aCaretPoint) {
+  MOZ_ASSERT(aHTMLEditor.IsEditActionDataAvailable());
+
+  // At edge of our block.  Look beside it and see if we can join to an
+  // adjacent block
+  mMode = Mode::JoinCurrentBlock;
+
+  // Don't break the basic structure of the HTML document.
+  if (aCurrentBlockElement.IsAnyOfHTMLElements(nsGkAtoms::html, nsGkAtoms::head,
+                                               nsGkAtoms::body)) {
+    return false;
+  }
+
+  // Make sure it's not a table element.  If so, cancel the operation
+  // (translation: users cannot backspace or delete across table cells)
+  if (HTMLEditUtils::IsAnyTableElement(&aCurrentBlockElement)) {
+    return false;
+  }
+
+  Element* editingHost = aHTMLEditor.ComputeEditingHost();
+  if (NS_WARN_IF(!editingHost)) {
+    return false;
+  }
+
+  auto ScanJoinTarget = [&]() -> nsIContent* {
+    nsIContent* targetContent =
+        aDirectionAndAmount == nsIEditor::ePrevious
+            ? HTMLEditUtils::GetPreviousContent(
+                  aCurrentBlockElement, {WalkTreeOption::IgnoreNonEditableNode},
+                  editingHost)
+            : HTMLEditUtils::GetNextContent(
+                  aCurrentBlockElement, {WalkTreeOption::IgnoreNonEditableNode},
+                  editingHost);
+    // If found content is an invisible text node, let's scan visible things.
+    auto IsIgnorableDataNode = [](nsIContent* aContent) {
+      return aContent && HTMLEditUtils::IsRemovableNode(*aContent) &&
+             ((aContent->IsText() &&
+               aContent->AsText()->TextIsOnlyWhitespace() &&
+               !HTMLEditUtils::IsVisibleTextNode(*aContent->AsText())) ||
+              (aContent->IsCharacterData() && !aContent->IsText()));
+    };
+    if (!IsIgnorableDataNode(targetContent)) {
+      return targetContent;
+    }
+    MOZ_ASSERT(mSkippedInvisibleContents.IsEmpty());
+    for (nsIContent* adjacentContent =
+             aDirectionAndAmount == nsIEditor::ePrevious
+                 ? HTMLEditUtils::GetPreviousContent(
+                       *targetContent, {WalkTreeOption::StopAtBlockBoundary},
+                       editingHost)
+                 : HTMLEditUtils::GetNextContent(
+                       *targetContent, {WalkTreeOption::StopAtBlockBoundary},
+                       editingHost);
+         adjacentContent;
+         adjacentContent =
+             aDirectionAndAmount == nsIEditor::ePrevious
+                 ? HTMLEditUtils::GetPreviousContent(
+                       *adjacentContent, {WalkTreeOption::StopAtBlockBoundary},
+                       editingHost)
+                 : HTMLEditUtils::GetNextContent(
+                       *adjacentContent, {WalkTreeOption::StopAtBlockBoundary},
+                       editingHost)) {
+      // If non-editable element is found, we should not skip it to avoid
+      // joining too far nodes.
+      if (!HTMLEditUtils::IsSimplyEditableNode(*adjacentContent)) {
+        break;
+      }
+      // If block element is found, we should join last leaf content in it.
+      if (HTMLEditUtils::IsBlockElement(*adjacentContent)) {
+        nsIContent* leafContent =
+            aDirectionAndAmount == nsIEditor::ePrevious
+                ? HTMLEditUtils::GetLastLeafContent(
+                      *adjacentContent, {LeafNodeType::OnlyEditableLeafNode})
+                : HTMLEditUtils::GetFirstLeafContent(
+                      *adjacentContent, {LeafNodeType::OnlyEditableLeafNode});
+        mSkippedInvisibleContents.AppendElement(*targetContent);
+        return leafContent ? leafContent : adjacentContent;
+      }
+      // Only when the found node is an invisible text node or a non-text data
+      // node, we should keep scanning.
+      if (IsIgnorableDataNode(adjacentContent)) {
+        mSkippedInvisibleContents.AppendElement(*targetContent);
+        targetContent = adjacentContent;
+        continue;
+      }
+      // Otherwise, we find a visible things. We should join with last found
+      // invisible text node.
+      break;
+    }
+    return targetContent;
+  };
+
+  if (aDirectionAndAmount == nsIEditor::ePrevious) {
+    mLeftContent = ScanJoinTarget();
+    mRightContent = aCaretPoint.GetContainerAs<nsIContent>();
+  } else {
+    mRightContent = ScanJoinTarget();
+    mLeftContent = aCaretPoint.GetContainerAs<nsIContent>();
+  }
+
+  // Nothing to join
+  if (!mLeftContent || !mRightContent) {
+    return false;
+  }
+
+  // Don't cross table boundaries.
+  return HTMLEditUtils::GetInclusiveAncestorAnyTableElement(*mLeftContent) ==
+         HTMLEditUtils::GetInclusiveAncestorAnyTableElement(*mRightContent);
+}
+
+nsresult HTMLEditor::AutoDeleteRangesHandler::AutoBlockElementsJoiner::
+    ComputeRangesToDeleteAtCurrentBlockBoundary(
+        const HTMLEditor& aHTMLEditor, const EditorDOMPoint& aCaretPoint,
+        AutoRangeArray& aRangesToDelete, const Element& aEditingHost) const {
+  MOZ_ASSERT(mLeftContent);
+  MOZ_ASSERT(mRightContent);
+
+  AutoInclusiveAncestorBlockElementsJoiner joiner(*mLeftContent,
+                                                  *mRightContent);
+  Result<bool, nsresult> canJoinThem =
+      joiner.Prepare(aHTMLEditor, aEditingHost);
+  if (canJoinThem.isErr()) {
+    NS_WARNING("AutoInclusiveAncestorBlockElementsJoiner::Prepare() failed");
+    return canJoinThem.unwrapErr();
+  }
+  if (canJoinThem.inspect()) {
+    nsresult rv =
+        joiner.ComputeRangesToDelete(aHTMLEditor, aCaretPoint, aRangesToDelete);
+    NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                         "AutoInclusiveAncestorBlockElementsJoiner::"
+                         "ComputeRangesToDelete() failed");
+    return rv;
+  }
+
+  // In this case, nothing will be deleted so that the affected range should
+  // be collapsed.
+  nsresult rv = aRangesToDelete.Collapse(aCaretPoint);
+  NS_WARNING_ASSERTION(NS_SUCCEEDED(rv), "AutoRangeArray::Collapse() failed");
+  return rv;
+}
+
+Result<EditActionResult, nsresult> HTMLEditor::AutoDeleteRangesHandler::
+    AutoBlockElementsJoiner::HandleDeleteAtCurrentBlockBoundary(
+        HTMLEditor& aHTMLEditor, nsIEditor::EDirection aDirectionAndAmount,
+        const EditorDOMPoint& aCaretPoint, const Element& aEditingHost) {
+  MOZ_ASSERT(mLeftContent);
+  MOZ_ASSERT(mRightContent);
+
+  AutoInclusiveAncestorBlockElementsJoiner joiner(*mLeftContent,
+                                                  *mRightContent);
+  Result<bool, nsresult> canJoinThem =
+      joiner.Prepare(aHTMLEditor, aEditingHost);
+  if (MOZ_UNLIKELY(canJoinThem.isErr())) {
+    NS_WARNING("AutoInclusiveAncestorBlockElementsJoiner::Prepare() failed");
+    return Err(canJoinThem.unwrapErr());
+  }
+
+  if (!canJoinThem.inspect()) {
+    nsresult rv = aHTMLEditor.CollapseSelectionTo(aCaretPoint);
+    if (NS_WARN_IF(rv == NS_ERROR_EDITOR_DESTROYED)) {
+      return Err(NS_ERROR_EDITOR_DESTROYED);
+    }
+    NS_WARNING_ASSERTION(
+        NS_SUCCEEDED(rv),
+        "EditorBase::CollapseSelectionTo() failed, but ignored");
+    return EditActionResult::CanceledResult();
+  }
+
+  EditActionResult result = EditActionResult::IgnoredResult();
+  EditorDOMPoint pointToPutCaret(aCaretPoint);
+  if (joiner.CanJoinBlocks()) {
+    AutoTrackDOMPoint tracker(aHTMLEditor.RangeUpdaterRef(), &pointToPutCaret);
+    Result<EditActionResult, nsresult> joinResult =
+        joiner.Run(aHTMLEditor, aEditingHost);
+    if (MOZ_UNLIKELY(joinResult.isErr())) {
+      NS_WARNING("AutoInclusiveAncestorBlockElementsJoiner::Run() failed");
+      return joinResult;
+    }
+    result |= joinResult.unwrap();
+#ifdef DEBUG
+    if (joiner.ShouldDeleteLeafContentInstead()) {
+      NS_ASSERTION(result.Ignored(),
+                   "Assumed `AutoInclusiveAncestorBlockElementsJoiner::Run()` "
+                   "returning ignored, but returned not ignored");
+    } else {
+      NS_ASSERTION(!result.Ignored(),
+                   "Assumed `AutoInclusiveAncestorBlockElementsJoiner::Run()` "
+                   "returning handled, but returned ignored");
+    }
+#endif  // #ifdef DEBUG
+
+    // Cleaning up invisible nodes which are skipped at scanning mLeftContent or
+    // mRightContent.
+    for (const OwningNonNull<nsIContent>& content : mSkippedInvisibleContents) {
+      nsresult rv =
+          aHTMLEditor.DeleteNodeWithTransaction(MOZ_KnownLive(content));
+      if (NS_FAILED(rv)) {
+        NS_WARNING("EditorBase::DeleteNodeWithTransaction() failed");
+        return Err(rv);
+      }
+    }
+    mSkippedInvisibleContents.Clear();
+
+    // If we're deleting selection (not replacing with new content) and
+    // AutoInclusiveAncestorBlockElementsJoiner computed new caret position, we
+    // should use it.  Otherwise, we should keep the our traditional behavior.
+    if (result.Handled() && joiner.PointRefToPutCaret().IsSet()) {
+      nsresult rv =
+          aHTMLEditor.CollapseSelectionTo(joiner.PointRefToPutCaret());
+      if (NS_WARN_IF(rv == NS_ERROR_EDITOR_DESTROYED)) {
+        return Err(NS_ERROR_EDITOR_DESTROYED);
+      }
+      if (NS_FAILED(rv)) {
+        NS_WARNING("EditorBase::CollapseSelectionTo() failed, but ignored");
+        return result;
+      }
+      // If we prefer to use style in the previous line, we should forget
+      // previous styles since the caret position has all styles which we want
+      // to use with new content.
+      if (nsIEditor::DirectionIsBackspace(aDirectionAndAmount)) {
+        aHTMLEditor.TopLevelEditSubActionDataRef()
+            .mCachedPendingStyles->Clear();
+      }
+      // And we don't want to keep extending a link at ex-end of the previous
+      // paragraph.
+      if (HTMLEditor::GetLinkElement(
+              joiner.PointRefToPutCaret().GetContainer())) {
+        aHTMLEditor.mPendingStylesToApplyToNewContent
+            ->ClearLinkAndItsSpecifiedStyle();
+      }
+      return result;
+    }
+  }
+  // This should claim that trying to join the block means that
+  // this handles the action because the caller shouldn't do anything
+  // anymore in this case.
+  result.MarkAsHandled();
+
+  nsresult rv = aHTMLEditor.CollapseSelectionTo(pointToPutCaret);
+  if (NS_WARN_IF(rv == NS_ERROR_EDITOR_DESTROYED)) {
+    return Err(NS_ERROR_EDITOR_DESTROYED);
+  }
+  NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                       "EditorBase::CollapseSelectionTo() failed, but ignored");
+  return result;
+}
+
+nsresult
+HTMLEditor::AutoDeleteRangesHandler::ComputeRangesToDeleteNonCollapsedRanges(
+    const HTMLEditor& aHTMLEditor, nsIEditor::EDirection aDirectionAndAmount,
+    AutoRangeArray& aRangesToDelete,
+    AutoDeleteRangesHandler::SelectionWasCollapsed aSelectionWasCollapsed,
+    const Element& aEditingHost) const {
+  MOZ_ASSERT(!aRangesToDelete.IsCollapsed());
+
+  if (NS_WARN_IF(!aRangesToDelete.FirstRangeRef()->StartRef().IsSet()) ||
+      NS_WARN_IF(!aRangesToDelete.FirstRangeRef()->EndRef().IsSet())) {
+    return NS_ERROR_FAILURE;
+  }
+
+  if (aRangesToDelete.Ranges().Length() == 1) {
+    nsFrameSelection* frameSelection =
+        aHTMLEditor.SelectionRef().GetFrameSelection();
+    if (NS_WARN_IF(!frameSelection)) {
+      return NS_ERROR_FAILURE;
+    }
+    Result<EditorRawDOMRange, nsresult> result = ExtendOrShrinkRangeToDelete(
+        aHTMLEditor, frameSelection,
+        EditorRawDOMRange(aRangesToDelete.FirstRangeRef()));
+    if (MOZ_UNLIKELY(result.isErr())) {
+      NS_WARNING(
+          "AutoDeleteRangesHandler::ExtendOrShrinkRangeToDelete() failed");
+      return NS_ERROR_FAILURE;
+    }
+    EditorRawDOMRange newRange(result.unwrap());
+    if (MOZ_UNLIKELY(NS_FAILED(aRangesToDelete.FirstRangeRef()->SetStartAndEnd(
+            newRange.StartRef().ToRawRangeBoundary(),
+            newRange.EndRef().ToRawRangeBoundary())))) {
+      NS_WARNING("nsRange::SetStartAndEnd() failed");
+      return NS_ERROR_FAILURE;
+    }
+    if (MOZ_UNLIKELY(
+            NS_WARN_IF(!aRangesToDelete.FirstRangeRef()->IsPositioned()))) {
+      return NS_ERROR_FAILURE;
+    }
+    if (NS_WARN_IF(aRangesToDelete.FirstRangeRef()->Collapsed())) {
+      return NS_OK;  // Hmm, there is nothing to delete...?
+    }
+  }
+
+  if (!aHTMLEditor.IsInPlaintextMode()) {
+    EditorDOMRange firstRange(aRangesToDelete.FirstRangeRef());
+    EditorDOMRange extendedRange =
+        WSRunScanner::GetRangeContainingInvisibleWhiteSpacesAtRangeBoundaries(
+            aHTMLEditor.ComputeEditingHost(),
+            EditorDOMRange(aRangesToDelete.FirstRangeRef()));
+    if (firstRange != extendedRange) {
+      nsresult rv = aRangesToDelete.FirstRangeRef()->SetStartAndEnd(
+          extendedRange.StartRef().ToRawRangeBoundary(),
+          extendedRange.EndRef().ToRawRangeBoundary());
+      if (NS_FAILED(rv)) {
+        NS_WARNING("nsRange::SetStartAndEnd() failed");
+        return NS_ERROR_FAILURE;
+      }
+    }
+  }
+
+  if (aRangesToDelete.FirstRangeRef()->GetStartContainer() ==
+      aRangesToDelete.FirstRangeRef()->GetEndContainer()) {
+    if (!aRangesToDelete.FirstRangeRef()->Collapsed()) {
+      nsresult rv = ComputeRangesToDeleteRangesWithTransaction(
+          aHTMLEditor, aDirectionAndAmount, aRangesToDelete);
+      NS_WARNING_ASSERTION(
+          NS_SUCCEEDED(rv),
+          "AutoDeleteRangesHandler::ComputeRangesToDeleteRangesWithTransaction("
+          ") failed");
+      return rv;
+    }
+    // `DeleteUnnecessaryNodesAndCollapseSelection()` may delete parent
+    // elements, but it does not affect computing target ranges.  Therefore,
+    // we don't need to touch aRangesToDelete in this case.
+    return NS_OK;
+  }
+
+  Element* startCiteNode = aHTMLEditor.GetMostDistantAncestorMailCiteElement(
+      *aRangesToDelete.FirstRangeRef()->GetStartContainer());
+  Element* endCiteNode = aHTMLEditor.GetMostDistantAncestorMailCiteElement(
+      *aRangesToDelete.FirstRangeRef()->GetEndContainer());
+
+  if (startCiteNode && !endCiteNode) {
+    aDirectionAndAmount = nsIEditor::eNext;
+  } else if (!startCiteNode && endCiteNode) {
+    aDirectionAndAmount = nsIEditor::ePrevious;
+  }
+
+  AutoBlockElementsJoiner joiner(*this);
+  if (!joiner.PrepareToDeleteNonCollapsedRanges(aHTMLEditor, aRangesToDelete)) {
+    return NS_ERROR_FAILURE;
+  }
+  nsresult rv = joiner.ComputeRangesToDelete(
+      aHTMLEditor, aDirectionAndAmount, aRangesToDelete, aSelectionWasCollapsed,
+      aEditingHost);
+  NS_WARNING_ASSERTION(
+      NS_SUCCEEDED(rv),
+      "AutoBlockElementsJoiner::ComputeRangesToDelete() failed");
+  return rv;
+}
+
+Result<EditActionResult, nsresult>
+HTMLEditor::AutoDeleteRangesHandler::HandleDeleteNonCollapsedRanges(
+    HTMLEditor& aHTMLEditor, nsIEditor::EDirection aDirectionAndAmount,
+    nsIEditor::EStripWrappers aStripWrappers, AutoRangeArray& aRangesToDelete,
+    SelectionWasCollapsed aSelectionWasCollapsed, const Element& aEditingHost) {
+  MOZ_ASSERT(aHTMLEditor.IsTopLevelEditSubActionDataAvailable());
+  MOZ_ASSERT(!aRangesToDelete.IsCollapsed());
+
+  if (NS_WARN_IF(!aRangesToDelete.FirstRangeRef()->StartRef().IsSet()) ||
+      NS_WARN_IF(!aRangesToDelete.FirstRangeRef()->EndRef().IsSet())) {
+    return Err(NS_ERROR_FAILURE);
+  }
+
+  MOZ_ASSERT_IF(aRangesToDelete.Ranges().Length() == 1,
+                aRangesToDelete.IsFirstRangeEditable(aEditingHost));
+
+  // Else we have a non-collapsed selection.  First adjust the selection.
+  // XXX Why do we extend selection only when there is only one range?
+  if (aRangesToDelete.Ranges().Length() == 1) {
+    nsFrameSelection* frameSelection =
+        aHTMLEditor.SelectionRef().GetFrameSelection();
+    if (NS_WARN_IF(!frameSelection)) {
+      return Err(NS_ERROR_FAILURE);
+    }
+    Result<EditorRawDOMRange, nsresult> result = ExtendOrShrinkRangeToDelete(
+        aHTMLEditor, frameSelection,
+        EditorRawDOMRange(aRangesToDelete.FirstRangeRef()));
+    if (MOZ_UNLIKELY(result.isErr())) {
+      NS_WARNING(
+          "AutoDeleteRangesHandler::ExtendOrShrinkRangeToDelete() failed");
+      return Err(NS_ERROR_FAILURE);
+    }
+    EditorRawDOMRange newRange(result.unwrap());
+    if (NS_FAILED(aRangesToDelete.FirstRangeRef()->SetStartAndEnd(
+            newRange.StartRef().ToRawRangeBoundary(),
+            newRange.EndRef().ToRawRangeBoundary()))) {
+      NS_WARNING("nsRange::SetStartAndEnd() failed");
+      return Err(NS_ERROR_FAILURE);
+    }
+    if (NS_WARN_IF(!aRangesToDelete.FirstRangeRef()->IsPositioned())) {
+      return Err(NS_ERROR_FAILURE);
+    }
+    if (NS_WARN_IF(aRangesToDelete.FirstRangeRef()->Collapsed())) {
+      // Hmm, there is nothing to delete...?
+      // In this case, the callers want collapsed selection.  Therefore, we need
+      // to change the `Selection` here.
+      nsresult rv = aHTMLEditor.CollapseSelectionTo(
+          aRangesToDelete.GetFirstRangeStartPoint<EditorRawDOMPoint>());
+      if (NS_FAILED(rv)) {
+        NS_WARNING("EditorBase::CollapseSelectionTo() failed");
+        return Err(rv);
+      }
+      return EditActionResult::HandledResult();
+    }
+    MOZ_ASSERT(aRangesToDelete.IsFirstRangeEditable(aEditingHost));
+  }
+
+  // Remember that we did a ranged delete for the benefit of AfterEditInner().
+  aHTMLEditor.TopLevelEditSubActionDataRef().mDidDeleteNonCollapsedRange = true;
+
+  // Figure out if the endpoints are in nodes that can be merged.  Adjust
+  // surrounding white-space in preparation to delete selection.
+  if (!aHTMLEditor.IsInPlaintextMode()) {
+    {
+      AutoTrackDOMRange firstRangeTracker(aHTMLEditor.RangeUpdaterRef(),
+                                          &aRangesToDelete.FirstRangeRef());
+      Result<CaretPoint, nsresult> caretPointOrError =
+          WhiteSpaceVisibilityKeeper::PrepareToDeleteRange(
+              aHTMLEditor, EditorDOMRange(aRangesToDelete.FirstRangeRef()),
+              aEditingHost);
+      if (MOZ_UNLIKELY(caretPointOrError.isErr())) {
+        NS_WARNING("WhiteSpaceVisibilityKeeper::PrepareToDeleteRange() failed");
+        return caretPointOrError.propagateErr();
+      }
+      // Ignore caret point suggestion because there was
+      // AutoTransactionsConserveSelection.
+      caretPointOrError.unwrap().IgnoreCaretPointSuggestion();
+    }
+    if (NS_WARN_IF(!aRangesToDelete.FirstRangeRef()->IsPositioned()) ||
+        (aHTMLEditor.MayHaveMutationEventListeners() &&
+         NS_WARN_IF(!aRangesToDelete.IsFirstRangeEditable(aEditingHost)))) {
+      NS_WARNING(
+          "WhiteSpaceVisibilityKeeper::PrepareToDeleteRange() made the first "
+          "range invalid");
+      return Err(NS_ERROR_EDITOR_UNEXPECTED_DOM_TREE);
+    }
+  }
+
+  // XXX This is odd.  We do we simply use `DeleteRangesWithTransaction()`
+  //     only when **first** range is in same container?
+  if (aRangesToDelete.FirstRangeRef()->GetStartContainer() ==
+      aRangesToDelete.FirstRangeRef()->GetEndContainer()) {
+    // Because of previous DOM tree changes, the range may be collapsed.
+    // If we've already removed all contents in the range, we shouldn't
+    // delete anything around the caret.
+    if (!aRangesToDelete.FirstRangeRef()->Collapsed()) {
+      {
+        AutoTrackDOMRange firstRangeTracker(aHTMLEditor.RangeUpdaterRef(),
+                                            &aRangesToDelete.FirstRangeRef());
+        Result<CaretPoint, nsresult> caretPointOrError =
+            aHTMLEditor.DeleteRangesWithTransaction(
+                aDirectionAndAmount, aStripWrappers, aRangesToDelete);
+        if (MOZ_UNLIKELY(caretPointOrError.isErr())) {
+          NS_WARNING("EditorBase::DeleteRangesWithTransaction() failed");
+          return caretPointOrError.propagateErr();
+        }
+        nsresult rv = caretPointOrError.inspect().SuggestCaretPointTo(
+            aHTMLEditor, {SuggestCaret::OnlyIfHasSuggestion,
+                          SuggestCaret::OnlyIfTransactionsAllowedToDoIt,
+                          SuggestCaret::AndIgnoreTrivialError});
+        if (NS_FAILED(rv)) {
+          NS_WARNING("CaretPoint::SuggestCaretPointTo() failed");
+          return Err(rv);
+        }
+        NS_WARNING_ASSERTION(
+            rv != NS_SUCCESS_EDITOR_BUT_IGNORED_TRIVIAL_ERROR,
+            "CaretPoint::SuggestCaretPointTo() failed, but ignored");
+      }
+      if (NS_WARN_IF(!aRangesToDelete.FirstRangeRef()->IsPositioned()) ||
+          (aHTMLEditor.MayHaveMutationEventListeners(
+               NS_EVENT_BITS_MUTATION_NODEREMOVED |
+               NS_EVENT_BITS_MUTATION_NODEREMOVEDFROMDOCUMENT |
+               NS_EVENT_BITS_MUTATION_SUBTREEMODIFIED) &&
+           NS_WARN_IF(!aRangesToDelete.IsFirstRangeEditable(aEditingHost)))) {
+        NS_WARNING(
+            "EditorBase::DeleteRangesWithTransaction() made the first range "
+            "invalid");
+        return Err(NS_ERROR_EDITOR_UNEXPECTED_DOM_TREE);
+      }
+    }
+    // However, even if the range is removed, we may need to clean up the
+    // containers which become empty.
+    nsresult rv = DeleteUnnecessaryNodesAndCollapseSelection(
+        aHTMLEditor, aDirectionAndAmount,
+        EditorDOMPoint(aRangesToDelete.FirstRangeRef()->StartRef()),
+        EditorDOMPoint(aRangesToDelete.FirstRangeRef()->EndRef()));
+    if (NS_FAILED(rv)) {
+      NS_WARNING(
+          "AutoDeleteRangesHandler::DeleteUnnecessaryNodesAndCollapseSelection("
+          ") failed");
+      return Err(rv);
+    }
+    return EditActionResult::HandledResult();
+  }
+
+  if (NS_WARN_IF(
+          !aRangesToDelete.FirstRangeRef()->GetStartContainer()->IsContent()) ||
+      NS_WARN_IF(
+          !aRangesToDelete.FirstRangeRef()->GetEndContainer()->IsContent())) {
+    return Err(NS_ERROR_FAILURE);
+  }
+
+  // Figure out mailcite ancestors
+  RefPtr<Element> startCiteNode =
+      aHTMLEditor.GetMostDistantAncestorMailCiteElement(
+          *aRangesToDelete.FirstRangeRef()->GetStartContainer());
+  RefPtr<Element> endCiteNode =
+      aHTMLEditor.GetMostDistantAncestorMailCiteElement(
+          *aRangesToDelete.FirstRangeRef()->GetEndContainer());
+
+  // If we only have a mailcite at one of the two endpoints, set the
+  // directionality of the deletion so that the selection will end up
+  // outside the mailcite.
+  if (startCiteNode && !endCiteNode) {
+    aDirectionAndAmount = nsIEditor::eNext;
+  } else if (!startCiteNode && endCiteNode) {
+    aDirectionAndAmount = nsIEditor::ePrevious;
+  }
+
+  AutoBlockElementsJoiner joiner(*this);
+  if (!joiner.PrepareToDeleteNonCollapsedRanges(aHTMLEditor, aRangesToDelete)) {
+    return Err(NS_ERROR_FAILURE);
+  }
+  Result<EditActionResult, nsresult> result =
+      joiner.Run(aHTMLEditor, aDirectionAndAmount, aStripWrappers,
+                 aRangesToDelete, aSelectionWasCollapsed, aEditingHost);
+  NS_WARNING_ASSERTION(result.isOk(), "AutoBlockElementsJoiner::Run() failed");
+  return result;
+}
+
+bool HTMLEditor::AutoDeleteRangesHandler::AutoBlockElementsJoiner::
+    PrepareToDeleteNonCollapsedRanges(const HTMLEditor& aHTMLEditor,
+                                      const AutoRangeArray& aRangesToDelete) {
+  MOZ_ASSERT(aHTMLEditor.IsEditActionDataAvailable());
+  MOZ_ASSERT(!aRangesToDelete.IsCollapsed());
+
+  mLeftContent = HTMLEditUtils::GetInclusiveAncestorElement(
+      *aRangesToDelete.FirstRangeRef()->GetStartContainer()->AsContent(),
+      HTMLEditUtils::ClosestEditableBlockElement);
+  mRightContent = HTMLEditUtils::GetInclusiveAncestorElement(
+      *aRangesToDelete.FirstRangeRef()->GetEndContainer()->AsContent(),
+      HTMLEditUtils::ClosestEditableBlockElement);
+  // Note that mLeftContent and/or mRightContent can be nullptr if editing host
+  // is an inline element.  If both editable ancestor block is exactly same
+  // one or one reaches an inline editing host, we can just delete the content
+  // in ranges.
+  if (mLeftContent == mRightContent || !mLeftContent || !mRightContent) {
+    MOZ_ASSERT_IF(!mLeftContent || !mRightContent,
+                  aRangesToDelete.FirstRangeRef()
+                          ->GetStartContainer()
+                          ->AsContent()
+                          ->GetEditingHost() == aRangesToDelete.FirstRangeRef()
+                                                    ->GetEndContainer()
+                                                    ->AsContent()
+                                                    ->GetEditingHost());
+    mMode = Mode::DeleteContentInRanges;
+    return true;
+  }
+
+  // If left block and right block are adjuscent siblings and they are same
+  // type of elements, we can merge them after deleting the selected contents.
+  // MOOSE: this could conceivably screw up a table.. fix me.
+  if (mLeftContent->GetParentNode() == mRightContent->GetParentNode() &&
+      HTMLEditUtils::CanContentsBeJoined(*mLeftContent, *mRightContent) &&
+      // XXX What's special about these three types of block?
+      (mLeftContent->IsHTMLElement(nsGkAtoms::p) ||
+       HTMLEditUtils::IsListItem(mLeftContent) ||
+       HTMLEditUtils::IsHeader(*mLeftContent))) {
+    mMode = Mode::JoinBlocksInSameParent;
+    return true;
+  }
+
+  mMode = Mode::DeleteNonCollapsedRanges;
+  return true;
+}
+
+nsresult HTMLEditor::AutoDeleteRangesHandler::AutoBlockElementsJoiner::
+    ComputeRangesToDeleteContentInRanges(
+        const HTMLEditor& aHTMLEditor,
+        nsIEditor::EDirection aDirectionAndAmount,
+        AutoRangeArray& aRangesToDelete) const {
+  MOZ_ASSERT(aHTMLEditor.IsEditActionDataAvailable());
+  MOZ_ASSERT(!aRangesToDelete.IsCollapsed());
+  MOZ_ASSERT(mMode == Mode::DeleteContentInRanges);
+  MOZ_ASSERT(aRangesToDelete.FirstRangeRef()
+                 ->GetStartContainer()
+                 ->AsContent()
+                 ->GetEditingHost());
+  MOZ_ASSERT(aRangesToDelete.FirstRangeRef()
+                 ->GetStartContainer()
+                 ->AsContent()
+                 ->GetEditingHost() == aRangesToDelete.FirstRangeRef()
+                                           ->GetEndContainer()
+                                           ->AsContent()
+                                           ->GetEditingHost());
+  MOZ_ASSERT(!mLeftContent == !mRightContent);
+  MOZ_ASSERT_IF(mLeftContent, mLeftContent->IsElement());
+  MOZ_ASSERT_IF(mLeftContent, aRangesToDelete.FirstRangeRef()
+                                  ->GetStartContainer()
+                                  ->IsInclusiveDescendantOf(mLeftContent));
+  MOZ_ASSERT_IF(mRightContent, mRightContent->IsElement());
+  MOZ_ASSERT_IF(mRightContent, aRangesToDelete.FirstRangeRef()
+                                   ->GetEndContainer()
+                                   ->IsInclusiveDescendantOf(mRightContent));
+  MOZ_ASSERT_IF(!mLeftContent,
+                HTMLEditUtils::IsInlineElement(*aRangesToDelete.FirstRangeRef()
+                                                    ->GetStartContainer()
+                                                    ->AsContent()
+                                                    ->GetEditingHost()));
+
+  nsresult rv =
+      mDeleteRangesHandlerConst.ComputeRangesToDeleteRangesWithTransaction(
+          aHTMLEditor, aDirectionAndAmount, aRangesToDelete);
+  NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                       "AutoDeleteRangesHandler::"
+                       "ComputeRangesToDeleteRangesWithTransaction() failed");
+  return rv;
+}
+
+Result<EditActionResult, nsresult> HTMLEditor::AutoDeleteRangesHandler::
+    AutoBlockElementsJoiner::DeleteContentInRanges(
+        HTMLEditor& aHTMLEditor, nsIEditor::EDirection aDirectionAndAmount,
+        nsIEditor::EStripWrappers aStripWrappers,
+        AutoRangeArray& aRangesToDelete) {
+  MOZ_ASSERT(aHTMLEditor.IsEditActionDataAvailable());
+  MOZ_ASSERT(!aRangesToDelete.IsCollapsed());
+  MOZ_ASSERT(mMode == Mode::DeleteContentInRanges);
+  MOZ_ASSERT(mDeleteRangesHandler);
+  MOZ_ASSERT(aRangesToDelete.FirstRangeRef()
+                 ->GetStartContainer()
+                 ->AsContent()
+                 ->GetEditingHost());
+  MOZ_ASSERT(aRangesToDelete.FirstRangeRef()
+                 ->GetStartContainer()
+                 ->AsContent()
+                 ->GetEditingHost() == aRangesToDelete.FirstRangeRef()
+                                           ->GetEndContainer()
+                                           ->AsContent()
+                                           ->GetEditingHost());
+  MOZ_ASSERT_IF(mLeftContent, mLeftContent->IsElement());
+  MOZ_ASSERT_IF(mLeftContent, aRangesToDelete.FirstRangeRef()
+                                  ->GetStartContainer()
+                                  ->IsInclusiveDescendantOf(mLeftContent));
+  MOZ_ASSERT_IF(mRightContent, mRightContent->IsElement());
+  MOZ_ASSERT_IF(mRightContent, aRangesToDelete.FirstRangeRef()
+                                   ->GetEndContainer()
+                                   ->IsInclusiveDescendantOf(mRightContent));
+  MOZ_ASSERT_IF(!mLeftContent,
+                HTMLEditUtils::IsInlineElement(*aRangesToDelete.FirstRangeRef()
+                                                    ->GetStartContainer()
+                                                    ->AsContent()
+                                                    ->GetEditingHost()));
+
+  // XXX This is also odd.  We do we simply use
+  //     `DeleteRangesWithTransaction()` only when **first** range is in
+  //     same block?
+  {
+    AutoTrackDOMRange firstRangeTracker(aHTMLEditor.RangeUpdaterRef(),
+                                        &aRangesToDelete.FirstRangeRef());
+    Result<CaretPoint, nsresult> caretPointOrError =
+        aHTMLEditor.DeleteRangesWithTransaction(
+            aDirectionAndAmount, aStripWrappers, aRangesToDelete);
+    if (MOZ_UNLIKELY(caretPointOrError.isErr())) {
+      if (NS_WARN_IF(caretPointOrError.inspectErr() ==
+                     NS_ERROR_EDITOR_DESTROYED)) {
+        return Err(NS_ERROR_EDITOR_DESTROYED);
+      }
+      NS_WARNING(
+          "EditorBase::DeleteRangesWithTransaction() failed, but ignored");
+    } else {
+      nsresult rv = caretPointOrError.inspect().SuggestCaretPointTo(
+          aHTMLEditor, {SuggestCaret::OnlyIfHasSuggestion,
+                        SuggestCaret::OnlyIfTransactionsAllowedToDoIt,
+                        SuggestCaret::AndIgnoreTrivialError});
+      if (NS_FAILED(rv)) {
+        NS_WARNING("CaretPoint::SuggestCaretPointTo() failed");
+        return Err(rv);
+      }
+      NS_WARNING_ASSERTION(
+          rv != NS_SUCCESS_EDITOR_BUT_IGNORED_TRIVIAL_ERROR,
+          "CaretPoint::SuggestCaretPointTo() failed, but ignored");
+    }
+  }
+  nsresult rv =
+      mDeleteRangesHandler->DeleteUnnecessaryNodesAndCollapseSelection(
+          aHTMLEditor, aDirectionAndAmount,
+          EditorDOMPoint(aRangesToDelete.FirstRangeRef()->StartRef()),
+          EditorDOMPoint(aRangesToDelete.FirstRangeRef()->EndRef()));
+  if (NS_FAILED(rv)) {
+    NS_WARNING(
+        "AutoDeleteRangesHandler::DeleteUnnecessaryNodesAndCollapseSelection() "
+        "failed");
+    return Err(rv);
+  }
+  return EditActionResult::HandledResult();
+}
+
+nsresult HTMLEditor::AutoDeleteRangesHandler::AutoBlockElementsJoiner::
+    ComputeRangesToJoinBlockElementsInSameParent(
+        const HTMLEditor& aHTMLEditor,
+        nsIEditor::EDirection aDirectionAndAmount,
+        AutoRangeArray& aRangesToDelete) const {
+  MOZ_ASSERT(aHTMLEditor.IsEditActionDataAvailable());
+  MOZ_ASSERT(!aRangesToDelete.IsCollapsed());
+  MOZ_ASSERT(mMode == Mode::JoinBlocksInSameParent);
+  MOZ_ASSERT(mLeftContent);
+  MOZ_ASSERT(mLeftContent->IsElement());
+  MOZ_ASSERT(aRangesToDelete.FirstRangeRef()
+                 ->GetStartContainer()
+                 ->IsInclusiveDescendantOf(mLeftContent));
+  MOZ_ASSERT(mRightContent);
+  MOZ_ASSERT(mRightContent->IsElement());
+  MOZ_ASSERT(aRangesToDelete.FirstRangeRef()
+                 ->GetEndContainer()
+                 ->IsInclusiveDescendantOf(mRightContent));
+  MOZ_ASSERT(mLeftContent->GetParentNode() == mRightContent->GetParentNode());
+
+  nsresult rv =
+      mDeleteRangesHandlerConst.ComputeRangesToDeleteRangesWithTransaction(
+          aHTMLEditor, aDirectionAndAmount, aRangesToDelete);
+  NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                       "AutoDeleteRangesHandler::"
+                       "ComputeRangesToDeleteRangesWithTransaction() failed");
+  return rv;
+}
+
+Result<EditActionResult, nsresult> HTMLEditor::AutoDeleteRangesHandler::
+    AutoBlockElementsJoiner::JoinBlockElementsInSameParent(
+        HTMLEditor& aHTMLEditor, nsIEditor::EDirection aDirectionAndAmount,
+        nsIEditor::EStripWrappers aStripWrappers,
+        AutoRangeArray& aRangesToDelete,
+        SelectionWasCollapsed aSelectionWasCollapsed,
+        const Element& aEditingHost) {
+  MOZ_ASSERT(aHTMLEditor.IsEditActionDataAvailable());
+  MOZ_ASSERT(!aRangesToDelete.IsCollapsed());
+  MOZ_ASSERT(mMode == Mode::JoinBlocksInSameParent);
+  MOZ_ASSERT(mLeftContent);
+  MOZ_ASSERT(mLeftContent->IsElement());
+  MOZ_ASSERT(aRangesToDelete.FirstRangeRef()
+                 ->GetStartContainer()
+                 ->IsInclusiveDescendantOf(mLeftContent));
+  MOZ_ASSERT(mRightContent);
+  MOZ_ASSERT(mRightContent->IsElement());
+  MOZ_ASSERT(aRangesToDelete.FirstRangeRef()
+                 ->GetEndContainer()
+                 ->IsInclusiveDescendantOf(mRightContent));
+  MOZ_ASSERT(mLeftContent->GetParentNode() == mRightContent->GetParentNode());
+
+  const bool backspaceInRightBlock =
+      aSelectionWasCollapsed == SelectionWasCollapsed::Yes &&
+      nsIEditor::DirectionIsBackspace(aDirectionAndAmount);
+
+  Result<CaretPoint, nsresult> caretPointOrError =
+      aHTMLEditor.DeleteRangesWithTransaction(aDirectionAndAmount,
+                                              aStripWrappers, aRangesToDelete);
+  if (MOZ_UNLIKELY(caretPointOrError.isErr())) {
+    NS_WARNING("EditorBase::DeleteRangesWithTransaction() failed");
+    return caretPointOrError.propagateErr();
+  }
+
+  nsresult rv = caretPointOrError.inspect().SuggestCaretPointTo(
+      aHTMLEditor, {SuggestCaret::OnlyIfHasSuggestion,
+                    SuggestCaret::OnlyIfTransactionsAllowedToDoIt,
+                    SuggestCaret::AndIgnoreTrivialError});
+  if (NS_FAILED(rv)) {
+    NS_WARNING("CaretPoint::SuggestCaretPointTo() failed");
+    return Err(rv);
+  }
+  NS_WARNING_ASSERTION(rv != NS_SUCCESS_EDITOR_BUT_IGNORED_TRIVIAL_ERROR,
+                       "CaretPoint::SuggestCaretPointTo() failed, but ignored");
+
+  if (NS_WARN_IF(!mLeftContent->GetParentNode()) ||
+      NS_WARN_IF(!mRightContent->GetParentNode()) ||
+      NS_WARN_IF(mLeftContent->GetParentNode() !=
+                 mRightContent->GetParentNode())) {
+    return Err(NS_ERROR_EDITOR_UNEXPECTED_DOM_TREE);
+  }
+
+  auto startOfRightContent =
+      HTMLEditUtils::GetDeepestEditableStartPointOf<EditorDOMPoint>(
+          *mRightContent);
+  AutoTrackDOMPoint trackStartOfRightContent(aHTMLEditor.RangeUpdaterRef(),
+                                             &startOfRightContent);
+  Result<EditorDOMPoint, nsresult> atFirstChildOfTheLastRightNodeOrError =
+      JoinNodesDeepWithTransaction(aHTMLEditor, MOZ_KnownLive(*mLeftContent),
+                                   MOZ_KnownLive(*mRightContent));
+  if (MOZ_UNLIKELY(atFirstChildOfTheLastRightNodeOrError.isErr())) {
+    NS_WARNING("HTMLEditor::JoinNodesDeepWithTransaction() failed");
+    return atFirstChildOfTheLastRightNodeOrError.propagateErr();
+  }
+  MOZ_ASSERT(atFirstChildOfTheLastRightNodeOrError.inspect().IsSet());
+  trackStartOfRightContent.FlushAndStopTracking();
+  if (NS_WARN_IF(!startOfRightContent.IsSet()) ||
+      NS_WARN_IF(!startOfRightContent.GetContainer()->IsInComposedDoc())) {
+    return Err(NS_ERROR_EDITOR_UNEXPECTED_DOM_TREE);
+  }
+
+  // If we're deleting selection (not replacing with new content) and the joined
+  // point follows a text node, we should put caret to end of the preceding text
+  // node because the other browsers insert following inputs into there.
+  if (MayEditActionDeleteAroundCollapsedSelection(
+          aHTMLEditor.GetEditAction())) {
+    WSRunScanner scanner(&aEditingHost, startOfRightContent);
+    WSScanResult maybePreviousText =
+        scanner.ScanPreviousVisibleNodeOrBlockBoundaryFrom(startOfRightContent);
+    if (maybePreviousText.IsContentEditable() &&
+        maybePreviousText.InVisibleOrCollapsibleCharacters()) {
+      nsresult rv = aHTMLEditor.CollapseSelectionTo(
+          maybePreviousText.Point<EditorRawDOMPoint>());
+      if (NS_FAILED(rv)) {
+        NS_WARNING("EditorBase::CollapseSelectionTo() failed");
+        return Err(rv);
+      }
+      // If we prefer to use style in the previous line, we should forget
+      // previous styles since the caret position has all styles which we want
+      // to use with new content.
+      if (backspaceInRightBlock) {
+        aHTMLEditor.TopLevelEditSubActionDataRef()
+            .mCachedPendingStyles->Clear();
+      }
+      // And we don't want to keep extending a link at ex-end of the previous
+      // paragraph.
+      if (HTMLEditor::GetLinkElement(maybePreviousText.TextPtr())) {
+        aHTMLEditor.mPendingStylesToApplyToNewContent
+            ->ClearLinkAndItsSpecifiedStyle();
+      }
+      return EditActionResult::HandledResult();
+    }
+  }
+
+  // Otherwise, we should put caret at start of the right content.
+  rv = aHTMLEditor.CollapseSelectionTo(
+      atFirstChildOfTheLastRightNodeOrError.inspect());
+  if (NS_FAILED(rv)) {
+    NS_WARNING("EditorBase::CollapseSelectionTo() failed");
+    return Err(rv);
+  }
+  return EditActionResult::HandledResult();
+}
+
+Result<bool, nsresult>
+HTMLEditor::AutoDeleteRangesHandler::AutoBlockElementsJoiner::
+    ComputeRangesToDeleteNodesEntirelyInRangeButKeepTableStructure(
+        const HTMLEditor& aHTMLEditor, nsRange& aRange,
+        AutoDeleteRangesHandler::SelectionWasCollapsed aSelectionWasCollapsed)
+        const {
+  MOZ_ASSERT(aHTMLEditor.IsEditActionDataAvailable());
+
+  AutoTArray<OwningNonNull<nsIContent>, 10> arrayOfTopChildren;
+  DOMSubtreeIterator iter;
+  nsresult rv = iter.Init(aRange);
+  if (NS_FAILED(rv)) {
+    NS_WARNING("DOMSubtreeIterator::Init() failed");
+    return Err(rv);
+  }
+  iter.AppendAllNodesToArray(arrayOfTopChildren);
+  return NeedsToJoinNodesAfterDeleteNodesEntirelyInRangeButKeepTableStructure(
+      aHTMLEditor, arrayOfTopChildren, aSelectionWasCollapsed);
+}
+
+Result<bool, nsresult> HTMLEditor::AutoDeleteRangesHandler::
+    AutoBlockElementsJoiner::DeleteNodesEntirelyInRangeButKeepTableStructure(
+        HTMLEditor& aHTMLEditor, nsRange& aRange,
+        AutoDeleteRangesHandler::SelectionWasCollapsed aSelectionWasCollapsed) {
+  MOZ_ASSERT(aHTMLEditor.IsEditActionDataAvailable());
+
+  // Build a list of direct child nodes in the range
+  AutoTArray<OwningNonNull<nsIContent>, 10> arrayOfTopChildren;
+  DOMSubtreeIterator iter;
+  nsresult rv = iter.Init(aRange);
+  if (NS_FAILED(rv)) {
+    NS_WARNING("DOMSubtreeIterator::Init() failed");
+    return Err(rv);
+  }
+  iter.AppendAllNodesToArray(arrayOfTopChildren);
+
+  // Now that we have the list, delete non-table elements
+  bool needsToJoinLater =
+      NeedsToJoinNodesAfterDeleteNodesEntirelyInRangeButKeepTableStructure(
+          aHTMLEditor, arrayOfTopChildren, aSelectionWasCollapsed);
+  for (auto& content : arrayOfTopChildren) {
+    // XXX After here, the child contents in the array may have been moved
+    //     to somewhere or removed.  We should handle it.
+    //
+    // MOZ_KnownLive because 'arrayOfTopChildren' is guaranteed to
+    // keep it alive.
+    //
+    // Even with https://bugzilla.mozilla.org/show_bug.cgi?id=1620312 fixed
+    // this might need to stay, because 'arrayOfTopChildren' is not const,
+    // so it's not obvious how to prove via static analysis that it won't
+    // change and release us.
+    nsresult rv =
+        DeleteContentButKeepTableStructure(aHTMLEditor, MOZ_KnownLive(content));
+    if (NS_WARN_IF(rv == NS_ERROR_EDITOR_DESTROYED)) {
+      return Err(NS_ERROR_EDITOR_DESTROYED);
+    }
+    NS_WARNING_ASSERTION(
+        NS_SUCCEEDED(rv),
+        "AutoBlockElementsJoiner::DeleteContentButKeepTableStructure() failed, "
+        "but ignored");
+  }
+  return needsToJoinLater;
+}
+
+bool HTMLEditor::AutoDeleteRangesHandler::AutoBlockElementsJoiner::
+    NeedsToJoinNodesAfterDeleteNodesEntirelyInRangeButKeepTableStructure(
+        const HTMLEditor& aHTMLEditor,
+        const nsTArray<OwningNonNull<nsIContent>>& aArrayOfContents,
+        AutoDeleteRangesHandler::SelectionWasCollapsed aSelectionWasCollapsed)
+        const {
+  // If original selection was collapsed, we need always to join the nodes.
+  // XXX Why?
+  if (aSelectionWasCollapsed ==
+      AutoDeleteRangesHandler::SelectionWasCollapsed::No) {
+    return true;
+  }
+  // If something visible is deleted, no need to join.  Visible means
+  // all nodes except non-visible textnodes and breaks.
+  if (aArrayOfContents.IsEmpty()) {
+    return true;
+  }
+  for (const OwningNonNull<nsIContent>& content : aArrayOfContents) {
+    if (content->IsText()) {
+      if (HTMLEditUtils::IsInVisibleTextFrames(aHTMLEditor.GetPresContext(),
+                                               *content->AsText())) {
+        return false;
+      }
+      continue;
+    }
+    // XXX If it's an element node, we should check whether it has visible
+    //     frames or not.
+    if (!content->IsElement() ||
+        HTMLEditUtils::IsEmptyNode(
+            *content->AsElement(),
+            {EmptyCheckOption::TreatSingleBRElementAsVisible})) {
+      continue;
+    }
+    if (!HTMLEditUtils::IsInvisibleBRElement(*content)) {
+      return false;
+    }
+  }
+  return true;
+}
+
+nsresult HTMLEditor::AutoDeleteRangesHandler::AutoBlockElementsJoiner::
+    DeleteTextAtStartAndEndOfRange(HTMLEditor& aHTMLEditor, nsRange& aRange) {
+  EditorDOMPoint rangeStart(aRange.StartRef());
+  EditorDOMPoint rangeEnd(aRange.EndRef());
+  if (rangeStart.IsInTextNode() && !rangeStart.IsEndOfContainer()) {
+    // Delete to last character
+    OwningNonNull<Text> textNode = *rangeStart.ContainerAs<Text>();
+    Result<CaretPoint, nsresult> caretPointOrError =
+        aHTMLEditor.DeleteTextWithTransaction(
+            textNode, rangeStart.Offset(),
+            rangeStart.GetContainer()->Length() - rangeStart.Offset());
+    if (MOZ_UNLIKELY(caretPointOrError.isErr())) {
+      NS_WARNING("HTMLEditor::DeleteTextWithTransaction() failed");
+      return caretPointOrError.unwrapErr();
+    }
+    nsresult rv = caretPointOrError.inspect().SuggestCaretPointTo(
+        aHTMLEditor, {SuggestCaret::OnlyIfHasSuggestion,
+                      SuggestCaret::OnlyIfTransactionsAllowedToDoIt,
+                      SuggestCaret::AndIgnoreTrivialError});
+    if (NS_FAILED(rv)) {
+      NS_WARNING("CaretPoint::SuggestCaretPointTo() failed");
+      return rv;
+    }
+    NS_WARNING_ASSERTION(
+        rv != NS_SUCCESS_EDITOR_BUT_IGNORED_TRIVIAL_ERROR,
+        "CaretPoint::SuggestCaretPointTo() failed, but ignored");
+  }
+  if (rangeEnd.IsInTextNode() && !rangeEnd.IsStartOfContainer()) {
+    // Delete to first character
+    OwningNonNull<Text> textNode = *rangeEnd.ContainerAs<Text>();
+    Result<CaretPoint, nsresult> caretPointOrError =
+        aHTMLEditor.DeleteTextWithTransaction(textNode, 0, rangeEnd.Offset());
+    if (MOZ_UNLIKELY(caretPointOrError.isErr())) {
+      NS_WARNING("HTMLEditor::DeleteTextWithTransaction() failed");
+      return caretPointOrError.unwrapErr();
+    }
+    nsresult rv = caretPointOrError.inspect().SuggestCaretPointTo(
+        aHTMLEditor, {SuggestCaret::OnlyIfHasSuggestion,
+                      SuggestCaret::OnlyIfTransactionsAllowedToDoIt,
+                      SuggestCaret::AndIgnoreTrivialError});
+    if (NS_FAILED(rv)) {
+      NS_WARNING("CaretPoint::SuggestCaretPointTo() failed");
+      return rv;
+    }
+    NS_WARNING_ASSERTION(
+        rv != NS_SUCCESS_EDITOR_BUT_IGNORED_TRIVIAL_ERROR,
+        "CaretPoint::SuggestCaretPointTo() failed, but ignored");
+  }
+  return NS_OK;
+}
+
+nsresult HTMLEditor::AutoDeleteRangesHandler::AutoBlockElementsJoiner::
+    ComputeRangesToDeleteNonCollapsedRanges(
+        const HTMLEditor& aHTMLEditor,
+        nsIEditor::EDirection aDirectionAndAmount,
+        AutoRangeArray& aRangesToDelete,
+        AutoDeleteRangesHandler::SelectionWasCollapsed aSelectionWasCollapsed,
+        const Element& aEditingHost) const {
+  MOZ_ASSERT(aHTMLEditor.IsEditActionDataAvailable());
+  MOZ_ASSERT(!aRangesToDelete.IsCollapsed());
+  MOZ_ASSERT(mLeftContent);
+  MOZ_ASSERT(mLeftContent->IsElement());
+  MOZ_ASSERT(aRangesToDelete.FirstRangeRef()
+                 ->GetStartContainer()
+                 ->IsInclusiveDescendantOf(mLeftContent));
+  MOZ_ASSERT(mRightContent);
+  MOZ_ASSERT(mRightContent->IsElement());
+  MOZ_ASSERT(aRangesToDelete.FirstRangeRef()
+                 ->GetEndContainer()
+                 ->IsInclusiveDescendantOf(mRightContent));
+
+  for (OwningNonNull<nsRange>& range : aRangesToDelete.Ranges()) {
+    Result<bool, nsresult> result =
+        ComputeRangesToDeleteNodesEntirelyInRangeButKeepTableStructure(
+            aHTMLEditor, range, aSelectionWasCollapsed);
+    if (result.isErr()) {
+      NS_WARNING(
+          "AutoBlockElementsJoiner::"
+          "ComputeRangesToDeleteNodesEntirelyInRangeButKeepTableStructure() "
+          "failed");
+      return result.unwrapErr();
+    }
+    if (!result.unwrap()) {
+      return NS_OK;
+    }
+  }
+
+  AutoInclusiveAncestorBlockElementsJoiner joiner(*mLeftContent,
+                                                  *mRightContent);
+  Result<bool, nsresult> canJoinThem =
+      joiner.Prepare(aHTMLEditor, aEditingHost);
+  if (canJoinThem.isErr()) {
+    NS_WARNING("AutoInclusiveAncestorBlockElementsJoiner::Prepare() failed");
+    return canJoinThem.unwrapErr();
+  }
+
+  if (!canJoinThem.unwrap()) {
+    return NS_SUCCESS_DOM_NO_OPERATION;
+  }
+
+  if (!joiner.CanJoinBlocks()) {
+    return NS_OK;
+  }
+
+  nsresult rv = joiner.ComputeRangesToDelete(aHTMLEditor, EditorDOMPoint(),
+                                             aRangesToDelete);
+  NS_WARNING_ASSERTION(
+      NS_SUCCEEDED(rv),
+      "AutoInclusiveAncestorBlockElementsJoiner::ComputeRangesToDelete() "
+      "failed");
+  return rv;
+}
+
+Result<EditActionResult, nsresult> HTMLEditor::AutoDeleteRangesHandler::
+    AutoBlockElementsJoiner::HandleDeleteNonCollapsedRanges(
+        HTMLEditor& aHTMLEditor, nsIEditor::EDirection aDirectionAndAmount,
+        nsIEditor::EStripWrappers aStripWrappers,
+        AutoRangeArray& aRangesToDelete,
+        AutoDeleteRangesHandler::SelectionWasCollapsed aSelectionWasCollapsed,
+        const Element& aEditingHost) {
+  MOZ_ASSERT(aHTMLEditor.IsEditActionDataAvailable());
+  MOZ_ASSERT(!aRangesToDelete.IsCollapsed());
+  MOZ_ASSERT(mDeleteRangesHandler);
+  MOZ_ASSERT(mLeftContent);
+  MOZ_ASSERT(mLeftContent->IsElement());
+  MOZ_ASSERT(aRangesToDelete.FirstRangeRef()
+                 ->GetStartContainer()
+                 ->IsInclusiveDescendantOf(mLeftContent));
+  MOZ_ASSERT(mRightContent);
+  MOZ_ASSERT(mRightContent->IsElement());
+  MOZ_ASSERT(aRangesToDelete.FirstRangeRef()
+                 ->GetEndContainer()
+                 ->IsInclusiveDescendantOf(mRightContent));
+
+  const bool backspaceInRightBlock =
+      aSelectionWasCollapsed == SelectionWasCollapsed::Yes &&
+      nsIEditor::DirectionIsBackspace(aDirectionAndAmount);
+
+  // Otherwise, delete every nodes in all ranges, then, clean up something.
+  EditActionResult result = EditActionResult::IgnoredResult();
+  EditorDOMPoint pointToPutCaret;
+  while (true) {
+    AutoTrackDOMRange firstRangeTracker(aHTMLEditor.RangeUpdaterRef(),
+                                        &aRangesToDelete.FirstRangeRef());
+
+    bool joinInclusiveAncestorBlockElements = true;
+    for (auto& range : aRangesToDelete.Ranges()) {
+      Result<bool, nsresult> deleteResult =
+          DeleteNodesEntirelyInRangeButKeepTableStructure(
+              aHTMLEditor, MOZ_KnownLive(range), aSelectionWasCollapsed);
+      if (MOZ_UNLIKELY(deleteResult.isErr())) {
+        NS_WARNING(
+            "AutoBlockElementsJoiner::"
+            "DeleteNodesEntirelyInRangeButKeepTableStructure() failed");
+        return deleteResult.propagateErr();
+      }
+      // XXX Completely odd.  Why don't we join blocks around each range?
+      joinInclusiveAncestorBlockElements &= deleteResult.unwrap();
+    }
+
+    // Check endpoints for possible text deletion.  We can assume that if
+    // text node is found, we can delete to end or to begining as
+    // appropriate, since the case where both sel endpoints in same text
+    // node was already handled (we wouldn't be here)
+    nsresult rv = DeleteTextAtStartAndEndOfRange(
+        aHTMLEditor, MOZ_KnownLive(aRangesToDelete.FirstRangeRef()));
+    if (NS_FAILED(rv)) {
+      NS_WARNING(
+          "AutoBlockElementsJoiner::DeleteTextAtStartAndEndOfRange() failed");
+      return Err(rv);
+    }
+
+    if (!joinInclusiveAncestorBlockElements) {
+      break;
+    }
+
+    AutoInclusiveAncestorBlockElementsJoiner joiner(*mLeftContent,
+                                                    *mRightContent);
+    Result<bool, nsresult> canJoinThem =
+        joiner.Prepare(aHTMLEditor, aEditingHost);
+    if (canJoinThem.isErr()) {
+      NS_WARNING("AutoInclusiveAncestorBlockElementsJoiner::Prepare() failed");
+      return canJoinThem.propagateErr();
+    }
+
+    // If we're joining blocks: if deleting forward the selection should
+    // be collapsed to the end of the selection, if deleting backward the
+    // selection should be collapsed to the beginning of the selection.
+    // But if we're not joining then the selection should collapse to the
+    // beginning of the selection if we'redeleting forward, because the
+    // end of the selection will still be in the next block. And same
+    // thing for deleting backwards (selection should collapse to the end,
+    // because the beginning will still be in the first block). See Bug
+    // 507936.
+    if (aDirectionAndAmount == nsIEditor::eNext) {
+      aDirectionAndAmount = nsIEditor::ePrevious;
+    } else {
+      aDirectionAndAmount = nsIEditor::eNext;
+    }
+
+    if (!canJoinThem.inspect()) {
+      result.MarkAsCanceled();
+      break;
+    }
+
+    if (!joiner.CanJoinBlocks()) {
+      break;
+    }
+
+    Result<EditActionResult, nsresult> joinResult =
+        joiner.Run(aHTMLEditor, aEditingHost);
+    if (MOZ_UNLIKELY(joinResult.isErr())) {
+      NS_WARNING("AutoInclusiveAncestorBlockElementsJoiner::Run() failed");
+      return joinResult;
+    }
+    result |= joinResult.unwrap();
+#ifdef DEBUG
+    if (joiner.ShouldDeleteLeafContentInstead()) {
+      NS_ASSERTION(result.Ignored(),
+                   "Assumed `AutoInclusiveAncestorBlockElementsJoiner::Run()` "
+                   "returning ignored, but returned not ignored");
+    } else {
+      NS_ASSERTION(!result.Ignored(),
+                   "Assumed `AutoInclusiveAncestorBlockElementsJoiner::Run()` "
+                   "returning handled, but returned ignored");
+    }
+#endif  // #ifdef DEBUG
+    pointToPutCaret = joiner.PointRefToPutCaret();
+    break;
+  }
+
+  // If we're deleting selection (not replacing with new content) and
+  // AutoInclusiveAncestorBlockElementsJoiner computed new caret position, we
+  // should use it.  Otherwise, we should keep the traditional behavior.
+  if (result.Handled() && pointToPutCaret.IsSet()) {
+    EditorDOMRange range(aRangesToDelete.FirstRangeRef());
+    nsresult rv =
+        mDeleteRangesHandler->DeleteUnnecessaryNodes(aHTMLEditor, range);
+    if (NS_FAILED(rv)) {
+      NS_WARNING("AutoDeleteRangesHandler::DeleteUnnecessaryNodes() failed");
+      return Err(rv);
+    }
+    rv = aHTMLEditor.CollapseSelectionTo(pointToPutCaret);
+    if (NS_FAILED(rv)) {
+      NS_WARNING("EditorBase::CollapseSelectionTo() failed");
+      return Err(rv);
+    }
+    // If we prefer to use style in the previous line, we should forget
+    // previous styles since the caret position has all styles which we want
+    // to use with new content.
+    if (backspaceInRightBlock) {
+      aHTMLEditor.TopLevelEditSubActionDataRef().mCachedPendingStyles->Clear();
+    }
+    // And we don't want to keep extending a link at ex-end of the previous
+    // paragraph.
+    if (HTMLEditor::GetLinkElement(pointToPutCaret.GetContainer())) {
+      aHTMLEditor.mPendingStylesToApplyToNewContent
+          ->ClearLinkAndItsSpecifiedStyle();
+    }
+    return result;
+  }
+
+  nsresult rv =
+      mDeleteRangesHandler->DeleteUnnecessaryNodesAndCollapseSelection(
+          aHTMLEditor, aDirectionAndAmount,
+          EditorDOMPoint(aRangesToDelete.FirstRangeRef()->StartRef()),
+          EditorDOMPoint(aRangesToDelete.FirstRangeRef()->EndRef()));
+  if (NS_FAILED(rv)) {
+    NS_WARNING(
+        "AutoDeleteRangesHandler::DeleteUnnecessaryNodesAndCollapseSelection() "
+        "failed");
+    return Err(rv);
+  }
+
+  result.MarkAsHandled();
+  return result;
+}
+
+nsresult HTMLEditor::AutoDeleteRangesHandler::DeleteUnnecessaryNodes(
+    HTMLEditor& aHTMLEditor, EditorDOMRange& aRange) {
+  MOZ_ASSERT(aHTMLEditor.IsTopLevelEditSubActionDataAvailable());
+  MOZ_ASSERT(EditorUtils::IsEditableContent(
+      *aRange.StartRef().ContainerAs<nsIContent>(), EditorType::HTML));
+  MOZ_ASSERT(EditorUtils::IsEditableContent(
+      *aRange.EndRef().ContainerAs<nsIContent>(), EditorType::HTML));
+
+  // If we're handling DnD, this is called to delete dragging item from the
+  // tree.  In this case, we should remove parent blocks if it becomes empty.
+  if (aHTMLEditor.GetEditAction() == EditAction::eDrop ||
+      aHTMLEditor.GetEditAction() == EditAction::eDeleteByDrag) {
+    MOZ_ASSERT(aRange.Collapsed() ||
+               (aRange.StartRef().GetContainer()->GetNextSibling() ==
+                    aRange.EndRef().GetContainer() &&
+                aRange.StartRef().IsEndOfContainer() &&
+                aRange.EndRef().IsStartOfContainer()));
+    AutoTrackDOMRange trackRange(aHTMLEditor.RangeUpdaterRef(), &aRange);
+
+    nsresult rv = DeleteParentBlocksWithTransactionIfEmpty(aHTMLEditor,
+                                                           aRange.StartRef());
+    if (NS_FAILED(rv)) {
+      NS_WARNING(
+          "HTMLEditor::DeleteParentBlocksWithTransactionIfEmpty() failed");
+      return rv;
+    }
+    aHTMLEditor.TopLevelEditSubActionDataRef().mDidDeleteEmptyParentBlocks =
+        rv == NS_OK;
+    // If we removed parent blocks, Selection should be collapsed at where
+    // the most ancestor empty block has been.
+    if (aHTMLEditor.TopLevelEditSubActionDataRef()
+            .mDidDeleteEmptyParentBlocks) {
+      return NS_OK;
+    }
+  }
+
+  if (NS_WARN_IF(!aRange.IsInContentNodes()) ||
+      NS_WARN_IF(!EditorUtils::IsEditableContent(
+          *aRange.StartRef().ContainerAs<nsIContent>(), EditorType::HTML)) ||
+      NS_WARN_IF(!EditorUtils::IsEditableContent(
+          *aRange.EndRef().ContainerAs<nsIContent>(), EditorType::HTML))) {
+    return NS_ERROR_EDITOR_UNEXPECTED_DOM_TREE;
+  }
+
+  // We might have left only collapsed white-space in the start/end nodes
+  AutoTrackDOMRange trackRange(aHTMLEditor.RangeUpdaterRef(), &aRange);
+
+  OwningNonNull<nsIContent> startContainer =
+      *aRange.StartRef().ContainerAs<nsIContent>();
+  OwningNonNull<nsIContent> endContainer =
+      *aRange.EndRef().ContainerAs<nsIContent>();
+  nsresult rv =
+      DeleteNodeIfInvisibleAndEditableTextNode(aHTMLEditor, startContainer);
+  if (NS_WARN_IF(rv == NS_ERROR_EDITOR_DESTROYED)) {
+    return NS_ERROR_EDITOR_DESTROYED;
+  }
+  NS_WARNING_ASSERTION(
+      NS_SUCCEEDED(rv),
+      "AutoDeleteRangesHandler::DeleteNodeIfInvisibleAndEditableTextNode() "
+      "failed to remove start node, but ignored");
+  // If we've not handled the selection end container, and it's still
+  // editable, let's handle it.
+  if (aRange.InSameContainer() ||
+      !EditorUtils::IsEditableContent(
+          *aRange.EndRef().ContainerAs<nsIContent>(), EditorType::HTML)) {
+    return NS_OK;
+  }
+  rv = DeleteNodeIfInvisibleAndEditableTextNode(aHTMLEditor, endContainer);
+  if (NS_WARN_IF(rv == NS_ERROR_EDITOR_DESTROYED)) {
+    return NS_ERROR_EDITOR_DESTROYED;
+  }
+  NS_WARNING_ASSERTION(
+      NS_SUCCEEDED(rv),
+      "AutoDeleteRangesHandler::DeleteNodeIfInvisibleAndEditableTextNode() "
+      "failed to remove end node, but ignored");
+  return NS_OK;
+}
+
+nsresult
+HTMLEditor::AutoDeleteRangesHandler::DeleteUnnecessaryNodesAndCollapseSelection(
+    HTMLEditor& aHTMLEditor, nsIEditor::EDirection aDirectionAndAmount,
+    const EditorDOMPoint& aSelectionStartPoint,
+    const EditorDOMPoint& aSelectionEndPoint) {
+  EditorDOMRange range(aSelectionStartPoint, aSelectionEndPoint);
+  nsresult rv = DeleteUnnecessaryNodes(aHTMLEditor, range);
+  if (NS_FAILED(rv)) {
+    NS_WARNING("AutoDeleteRangesHandler::DeleteUnnecessaryNodes() failed");
+    return rv;
+  }
+
+  if (aHTMLEditor.GetEditAction() == EditAction::eDrop ||
+      aHTMLEditor.GetEditAction() == EditAction::eDeleteByDrag) {
+    // If we removed parent blocks, Selection should be collapsed at where
+    // the most ancestor empty block has been.
+    // XXX I think that if the range is not in active editing host, we should
+    // not try to collapse selection here.
+    if (aHTMLEditor.TopLevelEditSubActionDataRef()
+            .mDidDeleteEmptyParentBlocks) {
+      nsresult rv = aHTMLEditor.CollapseSelectionTo(range.StartRef());
+      NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                           "EditorBase::CollapseSelectionTo() failed");
+      return rv;
+    }
+  }
+
+  rv = aHTMLEditor.CollapseSelectionTo(
+      aDirectionAndAmount == nsIEditor::ePrevious ? range.EndRef()
+                                                  : range.StartRef());
+  NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                       "EditorBase::CollapseSelectionTo() failed");
+  return rv;
+}
+
+nsresult
+HTMLEditor::AutoDeleteRangesHandler::DeleteNodeIfInvisibleAndEditableTextNode(
+    HTMLEditor& aHTMLEditor, nsIContent& aContent) {
+  MOZ_ASSERT(aHTMLEditor.IsEditActionDataAvailable());
+
+  Text* text = aContent.GetAsText();
+  if (!text) {
+    return NS_OK;
+  }
+
+  if (!HTMLEditUtils::IsRemovableFromParentNode(*text) ||
+      HTMLEditUtils::IsVisibleTextNode(*text)) {
+    return NS_OK;
+  }
+
+  nsresult rv = aHTMLEditor.DeleteNodeWithTransaction(aContent);
+  NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                       "EditorBase::DeleteNodeWithTransaction() failed");
+  return rv;
+}
+
+nsresult
+HTMLEditor::AutoDeleteRangesHandler::DeleteParentBlocksWithTransactionIfEmpty(
+    HTMLEditor& aHTMLEditor, const EditorDOMPoint& aPoint) {
+  MOZ_ASSERT(aPoint.IsSet());
+  MOZ_ASSERT(aHTMLEditor.mPlaceholderBatch);
+
+  // First, check there is visible contents before the point in current block.
+  RefPtr<Element> editingHost = aHTMLEditor.ComputeEditingHost();
+  WSRunScanner wsScannerForPoint(editingHost, aPoint);
+  if (!wsScannerForPoint.StartsFromCurrentBlockBoundary()) {
+    // If there is visible node before the point, we shouldn't remove the
+    // parent block.
+    return NS_SUCCESS_EDITOR_ELEMENT_NOT_FOUND;
+  }
+  if (NS_WARN_IF(!wsScannerForPoint.GetStartReasonContent()) ||
+      NS_WARN_IF(!wsScannerForPoint.GetStartReasonContent()->GetParentNode())) {
+    return NS_ERROR_FAILURE;
+  }
+  if (editingHost == wsScannerForPoint.GetStartReasonContent()) {
+    // If we reach editing host, there is no parent blocks which can be removed.
+    return NS_SUCCESS_EDITOR_ELEMENT_NOT_FOUND;
+  }
+  if (HTMLEditUtils::IsTableCellOrCaption(
+          *wsScannerForPoint.GetStartReasonContent())) {
+    // If we reach a <td>, <th> or <caption>, we shouldn't remove it even
+    // becomes empty because removing such element changes the structure of
+    // the <table>.
+    return NS_SUCCESS_EDITOR_ELEMENT_NOT_FOUND;
+  }
+
+  // Next, check there is visible contents after the point in current block.
+  WSScanResult forwardScanFromPointResult =
+      wsScannerForPoint.ScanNextVisibleNodeOrBlockBoundaryFrom(aPoint);
+  if (forwardScanFromPointResult.Failed()) {
+    NS_WARNING("WSRunScanner::ScanNextVisibleNodeOrBlockBoundaryFrom() failed");
+    return NS_ERROR_FAILURE;
+  }
+  if (forwardScanFromPointResult.ReachedBRElement()) {
+    // XXX In my understanding, this is odd.  The end reason may not be
+    //     same as the reached <br> element because the equality is
+    //     guaranteed only when ReachedCurrentBlockBoundary() returns true.
+    //     However, looks like that this code assumes that
+    //     GetEndReasonContent() returns the (or a) <br> element.
+    NS_ASSERTION(wsScannerForPoint.GetEndReasonContent() ==
+                     forwardScanFromPointResult.BRElementPtr(),
+                 "End reason is not the reached <br> element");
+    // If the <br> element is visible, we shouldn't remove the parent block.
+    if (HTMLEditUtils::IsVisibleBRElement(
+            *wsScannerForPoint.GetEndReasonContent())) {
+      return NS_SUCCESS_EDITOR_ELEMENT_NOT_FOUND;
+    }
+    if (wsScannerForPoint.GetEndReasonContent()->GetNextSibling()) {
+      WSScanResult scanResult =
+          WSRunScanner::ScanNextVisibleNodeOrBlockBoundary(
+              editingHost, EditorRawDOMPoint::After(
+                               *wsScannerForPoint.GetEndReasonContent()));
+      if (scanResult.Failed()) {
+        NS_WARNING("WSRunScanner::ScanNextVisibleNodeOrBlockBoundary() failed");
+        return NS_ERROR_FAILURE;
+      }
+      if (!scanResult.ReachedCurrentBlockBoundary()) {
+        // If we couldn't reach the block's end after the invisible <br>,
+        // that means that there is visible content.
+        return NS_SUCCESS_EDITOR_ELEMENT_NOT_FOUND;
+      }
+    }
+  } else if (!forwardScanFromPointResult.ReachedCurrentBlockBoundary()) {
+    // If we couldn't reach the block's end, the block has visible content.
+    return NS_SUCCESS_EDITOR_ELEMENT_NOT_FOUND;
+  }
+
+  // Delete the parent block.
+  EditorDOMPoint nextPoint(
+      wsScannerForPoint.GetStartReasonContent()->GetParentNode(), 0);
+  nsresult rv = aHTMLEditor.DeleteNodeWithTransaction(
+      MOZ_KnownLive(*wsScannerForPoint.GetStartReasonContent()));
+  if (NS_FAILED(rv)) {
+    NS_WARNING("EditorBase::DeleteNodeWithTransaction() failed");
+    return rv;
+  }
+  // If we reach editing host, return NS_OK.
+  if (nextPoint.GetContainer() == editingHost) {
+    return NS_OK;
+  }
+
+  // Otherwise, we need to check whether we're still in empty block or not.
+
+  // If we have mutation event listeners, the next point is now outside of
+  // editing host or editing hos has been changed.
+  if (aHTMLEditor.MayHaveMutationEventListeners(
+          NS_EVENT_BITS_MUTATION_NODEREMOVED |
+          NS_EVENT_BITS_MUTATION_NODEREMOVEDFROMDOCUMENT |
+          NS_EVENT_BITS_MUTATION_SUBTREEMODIFIED)) {
+    Element* newEditingHost = aHTMLEditor.ComputeEditingHost();
+    if (NS_WARN_IF(!newEditingHost) ||
+        NS_WARN_IF(newEditingHost != editingHost)) {
+      return NS_ERROR_EDITOR_UNEXPECTED_DOM_TREE;
+    }
+    if (NS_WARN_IF(!EditorUtils::IsDescendantOf(*nextPoint.GetContainer(),
+                                                *newEditingHost))) {
+      return NS_ERROR_EDITOR_UNEXPECTED_DOM_TREE;
+    }
+  }
+
+  rv = DeleteParentBlocksWithTransactionIfEmpty(aHTMLEditor, nextPoint);
+  NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                       "AutoDeleteRangesHandler::"
+                       "DeleteParentBlocksWithTransactionIfEmpty() failed");
+  return rv;
+}
+
+nsresult
+HTMLEditor::AutoDeleteRangesHandler::ComputeRangesToDeleteRangesWithTransaction(
+    const HTMLEditor& aHTMLEditor, nsIEditor::EDirection aDirectionAndAmount,
+    AutoRangeArray& aRangesToDelete) const {
+  MOZ_ASSERT(aHTMLEditor.IsEditActionDataAvailable());
+  MOZ_ASSERT(!aRangesToDelete.Ranges().IsEmpty());
+
+  EditorBase::HowToHandleCollapsedRange howToHandleCollapsedRange =
+      EditorBase::HowToHandleCollapsedRangeFor(aDirectionAndAmount);
+  if (NS_WARN_IF(aRangesToDelete.IsCollapsed() &&
+                 howToHandleCollapsedRange ==
+                     EditorBase::HowToHandleCollapsedRange::Ignore)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  auto extendRangeToSelectCharacterForward =
+      [](nsRange& aRange, const EditorRawDOMPointInText& aCaretPoint) -> void {
+    const nsTextFragment& textFragment =
+        aCaretPoint.ContainerAs<Text>()->TextFragment();
+    if (!textFragment.GetLength()) {
+      return;
+    }
+    if (textFragment.IsHighSurrogateFollowedByLowSurrogateAt(
+            aCaretPoint.Offset())) {
+      DebugOnly<nsresult> rvIgnored = aRange.SetStartAndEnd(
+          aCaretPoint.ContainerAs<Text>(), aCaretPoint.Offset(),
+          aCaretPoint.ContainerAs<Text>(), aCaretPoint.Offset() + 2);
+      NS_WARNING_ASSERTION(NS_SUCCEEDED(rvIgnored),
+                           "nsRange::SetStartAndEnd() failed");
+      return;
+    }
+    DebugOnly<nsresult> rvIgnored = aRange.SetStartAndEnd(
+        aCaretPoint.ContainerAs<Text>(), aCaretPoint.Offset(),
+        aCaretPoint.ContainerAs<Text>(), aCaretPoint.Offset() + 1);
+    NS_WARNING_ASSERTION(NS_SUCCEEDED(rvIgnored),
+                         "nsRange::SetStartAndEnd() failed");
+  };
+  auto extendRangeToSelectCharacterBackward =
+      [](nsRange& aRange, const EditorRawDOMPointInText& aCaretPoint) -> void {
+    if (aCaretPoint.IsStartOfContainer()) {
+      return;
+    }
+    const nsTextFragment& textFragment =
+        aCaretPoint.ContainerAs<Text>()->TextFragment();
+    if (!textFragment.GetLength()) {
+      return;
+    }
+    if (textFragment.IsLowSurrogateFollowingHighSurrogateAt(
+            aCaretPoint.Offset() - 1)) {
+      DebugOnly<nsresult> rvIgnored = aRange.SetStartAndEnd(
+          aCaretPoint.ContainerAs<Text>(), aCaretPoint.Offset() - 2,
+          aCaretPoint.ContainerAs<Text>(), aCaretPoint.Offset());
+      NS_WARNING_ASSERTION(NS_SUCCEEDED(rvIgnored),
+                           "nsRange::SetStartAndEnd() failed");
+      return;
+    }
+    DebugOnly<nsresult> rvIgnored = aRange.SetStartAndEnd(
+        aCaretPoint.ContainerAs<Text>(), aCaretPoint.Offset() - 1,
+        aCaretPoint.ContainerAs<Text>(), aCaretPoint.Offset());
+    NS_WARNING_ASSERTION(NS_SUCCEEDED(rvIgnored),
+                         "nsRange::SetStartAndEnd() failed");
+  };
+
+  RefPtr<Element> editingHost = aHTMLEditor.ComputeEditingHost();
+  for (OwningNonNull<nsRange>& range : aRangesToDelete.Ranges()) {
+    // If it's not collapsed, `DeleteRangeTransaction::Create()` will be called
+    // with it and `DeleteRangeTransaction` won't modify the range.
+    if (!range->Collapsed()) {
+      continue;
+    }
+
+    if (howToHandleCollapsedRange ==
+        EditorBase::HowToHandleCollapsedRange::Ignore) {
+      continue;
+    }
+
+    // In the other cases, `EditorBase::CreateTransactionForCollapsedRange()`
+    // will handle the collapsed range.
+    EditorRawDOMPoint caretPoint(range->StartRef());
+    if (howToHandleCollapsedRange ==
+            EditorBase::HowToHandleCollapsedRange::ExtendBackward &&
+        caretPoint.IsStartOfContainer()) {
+      nsIContent* previousEditableContent = HTMLEditUtils::GetPreviousContent(
+          *caretPoint.GetContainer(), {WalkTreeOption::IgnoreNonEditableNode},
+          editingHost);
+      if (!previousEditableContent) {
+        continue;
+      }
+      if (!previousEditableContent->IsText()) {
+        IgnoredErrorResult ignoredError;
+        range->SelectNode(*previousEditableContent, ignoredError);
+        NS_WARNING_ASSERTION(!ignoredError.Failed(),
+                             "nsRange::SelectNode() failed");
+        continue;
+      }
+
+      extendRangeToSelectCharacterBackward(
+          range,
+          EditorRawDOMPointInText::AtEndOf(*previousEditableContent->AsText()));
+      continue;
+    }
+
+    if (howToHandleCollapsedRange ==
+            EditorBase::HowToHandleCollapsedRange::ExtendForward &&
+        caretPoint.IsEndOfContainer()) {
+      nsIContent* nextEditableContent = HTMLEditUtils::GetNextContent(
+          *caretPoint.GetContainer(), {WalkTreeOption::IgnoreNonEditableNode},
+          editingHost);
+      if (!nextEditableContent) {
+        continue;
+      }
+
+      if (!nextEditableContent->IsText()) {
+        IgnoredErrorResult ignoredError;
+        range->SelectNode(*nextEditableContent, ignoredError);
+        NS_WARNING_ASSERTION(!ignoredError.Failed(),
+                             "nsRange::SelectNode() failed");
+        continue;
+      }
+
+      extendRangeToSelectCharacterForward(
+          range, EditorRawDOMPointInText(nextEditableContent->AsText(), 0));
+      continue;
+    }
+
+    if (caretPoint.IsInTextNode()) {
+      if (howToHandleCollapsedRange ==
+          EditorBase::HowToHandleCollapsedRange::ExtendBackward) {
+        extendRangeToSelectCharacterBackward(
+            range, EditorRawDOMPointInText(caretPoint.ContainerAs<Text>(),
+                                           caretPoint.Offset()));
+        continue;
+      }
+      extendRangeToSelectCharacterForward(
+          range, EditorRawDOMPointInText(caretPoint.ContainerAs<Text>(),
+                                         caretPoint.Offset()));
+      continue;
+    }
+
+    nsIContent* editableContent =
+        howToHandleCollapsedRange ==
+                EditorBase::HowToHandleCollapsedRange::ExtendBackward
+            ? HTMLEditUtils::GetPreviousContent(
+                  caretPoint, {WalkTreeOption::IgnoreNonEditableNode},
+                  editingHost)
+            : HTMLEditUtils::GetNextContent(
+                  caretPoint, {WalkTreeOption::IgnoreNonEditableNode},
+                  editingHost);
+    if (!editableContent) {
+      continue;
+    }
+    while (editableContent && editableContent->IsCharacterData() &&
+           !editableContent->Length()) {
+      editableContent =
+          howToHandleCollapsedRange ==
+                  EditorBase::HowToHandleCollapsedRange::ExtendBackward
+              ? HTMLEditUtils::GetPreviousContent(
+                    *editableContent, {WalkTreeOption::IgnoreNonEditableNode},
+                    editingHost)
+              : HTMLEditUtils::GetNextContent(
+                    *editableContent, {WalkTreeOption::IgnoreNonEditableNode},
+                    editingHost);
+    }
+    if (!editableContent) {
+      continue;
+    }
+
+    if (!editableContent->IsText()) {
+      IgnoredErrorResult ignoredError;
+      range->SelectNode(*editableContent, ignoredError);
+      NS_WARNING_ASSERTION(!ignoredError.Failed(),
+                           "nsRange::SelectNode() failed");
+      continue;
+    }
+
+    if (howToHandleCollapsedRange ==
+        EditorBase::HowToHandleCollapsedRange::ExtendBackward) {
+      extendRangeToSelectCharacterBackward(
+          range, EditorRawDOMPointInText::AtEndOf(*editableContent->AsText()));
+      continue;
+    }
+    extendRangeToSelectCharacterForward(
+        range, EditorRawDOMPointInText(editableContent->AsText(), 0));
+  }
+
+  return NS_OK;
+}
+
+template <typename EditorDOMPointType>
+Result<CaretPoint, nsresult> HTMLEditor::DeleteTextAndTextNodesWithTransaction(
+    const EditorDOMPointType& aStartPoint, const EditorDOMPointType& aEndPoint,
+    TreatEmptyTextNodes aTreatEmptyTextNodes) {
+  if (NS_WARN_IF(!aStartPoint.IsSet()) || NS_WARN_IF(!aEndPoint.IsSet())) {
+    return Err(NS_ERROR_INVALID_ARG);
+  }
+
+  // MOOSE: this routine needs to be modified to preserve the integrity of the
+  // wsFragment info.
+
+  if (aStartPoint == aEndPoint) {
+    // Nothing to delete
+    return CaretPoint(EditorDOMPoint());
+  }
+
+  RefPtr<Element> editingHost = ComputeEditingHost();
+  auto DeleteEmptyContentNodeWithTransaction =
+      [this, &aTreatEmptyTextNodes, &editingHost](nsIContent& aContent)
+          MOZ_CAN_RUN_SCRIPT_FOR_DEFINITION -> nsresult {
+    OwningNonNull<nsIContent> nodeToRemove = aContent;
+    if (aTreatEmptyTextNodes ==
+        TreatEmptyTextNodes::RemoveAllEmptyInlineAncestors) {
+      Element* emptyParentElementToRemove =
+          HTMLEditUtils::GetMostDistantAncestorEditableEmptyInlineElement(
+              nodeToRemove, editingHost);
+      if (emptyParentElementToRemove) {
+        nodeToRemove = *emptyParentElementToRemove;
+      }
+    }
+    nsresult rv = DeleteNodeWithTransaction(nodeToRemove);
+    NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                         "EditorBase::DeleteNodeWithTransaction() failed");
+    return rv;
+  };
+
+  if (aStartPoint.GetContainer() == aEndPoint.GetContainer() &&
+      aStartPoint.IsInTextNode()) {
+    if (aTreatEmptyTextNodes !=
+            TreatEmptyTextNodes::KeepIfContainerOfRangeBoundaries &&
+        aStartPoint.IsStartOfContainer() && aEndPoint.IsEndOfContainer()) {
+      nsresult rv = DeleteEmptyContentNodeWithTransaction(
+          MOZ_KnownLive(*aStartPoint.template ContainerAs<Text>()));
+      if (NS_FAILED(rv)) {
+        NS_WARNING("deleteEmptyContentNodeWithTransaction() failed");
+        return Err(rv);
+      }
+      return CaretPoint(EditorDOMPoint());
+    }
+    RefPtr<Text> textNode = aStartPoint.template ContainerAs<Text>();
+    Result<CaretPoint, nsresult> caretPointOrError =
+        DeleteTextWithTransaction(*textNode, aStartPoint.Offset(),
+                                  aEndPoint.Offset() - aStartPoint.Offset());
+    NS_WARNING_ASSERTION(caretPointOrError.isOk(),
+                         "HTMLEditor::DeleteTextWithTransaction() failed");
+    return caretPointOrError;
+  }
+
+  RefPtr<nsRange> range =
+      nsRange::Create(aStartPoint.ToRawRangeBoundary(),
+                      aEndPoint.ToRawRangeBoundary(), IgnoreErrors());
+  if (!range) {
+    NS_WARNING("nsRange::Create() failed");
+    return Err(NS_ERROR_FAILURE);
+  }
+
+  // Collect editable text nodes in the given range.
+  AutoTArray<OwningNonNull<Text>, 16> arrayOfTextNodes;
+  DOMIterator iter;
+  if (NS_FAILED(iter.Init(*range))) {
+    return CaretPoint(EditorDOMPoint());  // Nothing to delete in the range.
+  }
+  iter.AppendNodesToArray(
+      +[](nsINode& aNode, void*) {
+        MOZ_ASSERT(aNode.IsText());
+        return HTMLEditUtils::IsSimplyEditableNode(aNode);
+      },
+      arrayOfTextNodes);
+  EditorDOMPoint pointToPutCaret;
+  for (OwningNonNull<Text>& textNode : arrayOfTextNodes) {
+    if (textNode == aStartPoint.GetContainer()) {
+      if (aStartPoint.IsEndOfContainer()) {
+        continue;
+      }
+      if (aStartPoint.IsStartOfContainer() &&
+          aTreatEmptyTextNodes !=
+              TreatEmptyTextNodes::KeepIfContainerOfRangeBoundaries) {
+        AutoTrackDOMPoint trackPointToPutCaret(RangeUpdaterRef(),
+                                               &pointToPutCaret);
+        nsresult rv = DeleteEmptyContentNodeWithTransaction(
+            MOZ_KnownLive(*aStartPoint.template ContainerAs<Text>()));
+        if (NS_FAILED(rv)) {
+          NS_WARNING("DeleteEmptyContentNodeWithTransaction() failed");
+          return Err(rv);
+        }
+        continue;
+      }
+      AutoTrackDOMPoint trackPointToPutCaret(RangeUpdaterRef(),
+                                             &pointToPutCaret);
+      Result<CaretPoint, nsresult> caretPointOrError =
+          DeleteTextWithTransaction(MOZ_KnownLive(textNode),
+                                    aStartPoint.Offset(),
+                                    textNode->Length() - aStartPoint.Offset());
+      if (MOZ_UNLIKELY(caretPointOrError.isErr())) {
+        NS_WARNING("HTMLEditor::DeleteTextWithTransaction() failed");
+        return caretPointOrError;
+      }
+      trackPointToPutCaret.FlushAndStopTracking();
+      caretPointOrError.unwrap().MoveCaretPointTo(
+          pointToPutCaret, {SuggestCaret::OnlyIfHasSuggestion});
+      continue;
+    }
+
+    if (textNode == aEndPoint.GetContainer()) {
+      if (aEndPoint.IsStartOfContainer()) {
+        break;
+      }
+      if (aEndPoint.IsEndOfContainer() &&
+          aTreatEmptyTextNodes !=
+              TreatEmptyTextNodes::KeepIfContainerOfRangeBoundaries) {
+        AutoTrackDOMPoint trackPointToPutCaret(RangeUpdaterRef(),
+                                               &pointToPutCaret);
+        nsresult rv = DeleteEmptyContentNodeWithTransaction(
+            MOZ_KnownLive(*aEndPoint.template ContainerAs<Text>()));
+        NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                             "DeleteEmptyContentNodeWithTransaction() failed");
+        return Err(rv);
+      }
+      AutoTrackDOMPoint trackPointToPutCaret(RangeUpdaterRef(),
+                                             &pointToPutCaret);
+      Result<CaretPoint, nsresult> caretPointOrError =
+          DeleteTextWithTransaction(MOZ_KnownLive(textNode), 0,
+                                    aEndPoint.Offset());
+      if (MOZ_UNLIKELY(caretPointOrError.isErr())) {
+        NS_WARNING("HTMLEditor::DeleteTextWithTransaction() failed");
+        return caretPointOrError;
+      }
+      trackPointToPutCaret.FlushAndStopTracking();
+      caretPointOrError.unwrap().MoveCaretPointTo(
+          pointToPutCaret, {SuggestCaret::OnlyIfHasSuggestion});
+      return CaretPoint(pointToPutCaret);
+    }
+
+    nsresult rv =
+        DeleteEmptyContentNodeWithTransaction(MOZ_KnownLive(textNode));
+    if (NS_FAILED(rv)) {
+      NS_WARNING("DeleteEmptyContentNodeWithTransaction() failed");
+      return Err(rv);
+    }
+  }
+
+  return CaretPoint(pointToPutCaret);
+}
+
+Result<EditorDOMPoint, nsresult> HTMLEditor::AutoDeleteRangesHandler::
+    AutoBlockElementsJoiner::JoinNodesDeepWithTransaction(
+        HTMLEditor& aHTMLEditor, nsIContent& aLeftContent,
+        nsIContent& aRightContent) {
+  // While the rightmost children and their descendants of the left node match
+  // the leftmost children and their descendants of the right node, join them
+  // up.
+
+  nsCOMPtr<nsIContent> leftContentToJoin = &aLeftContent;
+  nsCOMPtr<nsIContent> rightContentToJoin = &aRightContent;
+  nsCOMPtr<nsINode> parentNode = aRightContent.GetParentNode();
+
+  EditorDOMPoint ret;
+  while (leftContentToJoin && rightContentToJoin && parentNode &&
+         HTMLEditUtils::CanContentsBeJoined(*leftContentToJoin,
+                                            *rightContentToJoin)) {
+    // Do the join
+    Result<JoinNodesResult, nsresult> joinNodesResult =
+        aHTMLEditor.JoinNodesWithTransaction(*leftContentToJoin,
+                                             *rightContentToJoin);
+    if (MOZ_UNLIKELY(joinNodesResult.isErr())) {
+      NS_WARNING("HTMLEditor::JoinNodesWithTransaction() failed");
+      return joinNodesResult.propagateErr();
+    }
+
+    ret = joinNodesResult.inspect().AtJoinedPoint<EditorDOMPoint>();
+    if (NS_WARN_IF(!ret.IsSet())) {
+      return Err(NS_ERROR_FAILURE);
+    }
+
+    if (parentNode->IsText()) {
+      // We've joined all the way down to text nodes, we're done!
+      return ret;
+    }
+
+    // Get new left and right nodes, and begin anew
+    rightContentToJoin = ret.GetCurrentChildAtOffset();
+    if (rightContentToJoin) {
+      leftContentToJoin = rightContentToJoin->GetPreviousSibling();
+    } else {
+      leftContentToJoin = nullptr;
+    }
+
+    // Skip over non-editable nodes
+    while (leftContentToJoin && !EditorUtils::IsEditableContent(
+                                    *leftContentToJoin, EditorType::HTML)) {
+      leftContentToJoin = leftContentToJoin->GetPreviousSibling();
+    }
+    if (!leftContentToJoin) {
+      return ret;
+    }
+
+    while (rightContentToJoin && !EditorUtils::IsEditableContent(
+                                     *rightContentToJoin, EditorType::HTML)) {
+      rightContentToJoin = rightContentToJoin->GetNextSibling();
+    }
+    if (!rightContentToJoin) {
+      return ret;
+    }
+  }
+
+  if (!ret.IsSet()) {
+    NS_WARNING("HTMLEditor::JoinNodesDeepWithTransaction() joined no contents");
+    return Err(NS_ERROR_FAILURE);
+  }
+  return ret;
+}
+
+Result<bool, nsresult> HTMLEditor::AutoDeleteRangesHandler::
+    AutoBlockElementsJoiner::AutoInclusiveAncestorBlockElementsJoiner::Prepare(
+        const HTMLEditor& aHTMLEditor, const Element& aEditingHost) {
+  mLeftBlockElement = HTMLEditUtils::GetInclusiveAncestorElement(
+      mInclusiveDescendantOfLeftBlockElement,
+      HTMLEditUtils::ClosestEditableBlockElementExceptHRElement);
+  mRightBlockElement = HTMLEditUtils::GetInclusiveAncestorElement(
+      mInclusiveDescendantOfRightBlockElement,
+      HTMLEditUtils::ClosestEditableBlockElementExceptHRElement);
+
+  if (NS_WARN_IF(!IsSet())) {
+    mCanJoinBlocks = false;
+    return Err(NS_ERROR_UNEXPECTED);
+  }
+
+  // Don't join the blocks if both of them are basic structure of the HTML
+  // document (Note that `<body>` can be joined with its children).
+  if (mLeftBlockElement->IsAnyOfHTMLElements(nsGkAtoms::html, nsGkAtoms::head,
+                                             nsGkAtoms::body) &&
+      mRightBlockElement->IsAnyOfHTMLElements(nsGkAtoms::html, nsGkAtoms::head,
+                                              nsGkAtoms::body)) {
+    mCanJoinBlocks = false;
+    return false;
+  }
+
+  if (HTMLEditUtils::IsAnyTableElement(mLeftBlockElement) ||
+      HTMLEditUtils::IsAnyTableElement(mRightBlockElement)) {
+    // Do not try to merge table elements, cancel the deletion.
+    mCanJoinBlocks = false;
+    return false;
+  }
+
+  // Bail if both blocks the same
+  if (IsSameBlockElement()) {
+    mCanJoinBlocks = true;  // XXX Anyway, Run() will ingore this case.
+    mFallbackToDeleteLeafContent = true;
+    return true;
+  }
+
+  // Joining a list item to its parent is a NOP.
+  if (HTMLEditUtils::IsAnyListElement(mLeftBlockElement) &&
+      HTMLEditUtils::IsListItem(mRightBlockElement) &&
+      mRightBlockElement->GetParentNode() == mLeftBlockElement) {
+    mCanJoinBlocks = false;
+    return true;
+  }
+
+  // Special rule here: if we are trying to join list items, and they are in
+  // different lists, join the lists instead.
+  if (HTMLEditUtils::IsListItem(mLeftBlockElement) &&
+      HTMLEditUtils::IsListItem(mRightBlockElement)) {
+    // XXX leftListElement and/or rightListElement may be not list elements.
+    Element* leftListElement = mLeftBlockElement->GetParentElement();
+    Element* rightListElement = mRightBlockElement->GetParentElement();
+    EditorDOMPoint atChildInBlock;
+    if (leftListElement && rightListElement &&
+        leftListElement != rightListElement &&
+        !EditorUtils::IsDescendantOf(*leftListElement, *mRightBlockElement,
+                                     &atChildInBlock) &&
+        !EditorUtils::IsDescendantOf(*rightListElement, *mLeftBlockElement,
+                                     &atChildInBlock)) {
+      // There are some special complications if the lists are descendants of
+      // the other lists' items.  Note that it is okay for them to be
+      // descendants of the other lists themselves, which is the usual case for
+      // sublists in our implementation.
+      MOZ_DIAGNOSTIC_ASSERT(!atChildInBlock.IsSet());
+      mLeftBlockElement = leftListElement;
+      mRightBlockElement = rightListElement;
+      mNewListElementTagNameOfRightListElement =
+          Some(leftListElement->NodeInfo()->NameAtom());
+    }
+  }
+
+  if (!EditorUtils::IsDescendantOf(*mLeftBlockElement, *mRightBlockElement,
+                                   &mPointContainingTheOtherBlockElement)) {
+    Unused << EditorUtils::IsDescendantOf(
+        *mRightBlockElement, *mLeftBlockElement,
+        &mPointContainingTheOtherBlockElement);
+  }
+
+  if (mPointContainingTheOtherBlockElement.GetContainer() ==
+      mRightBlockElement) {
+    mPrecedingInvisibleBRElement =
+        WSRunScanner::GetPrecedingBRElementUnlessVisibleContentFound(
+            aHTMLEditor.ComputeEditingHost(),
+            EditorDOMPoint::AtEndOf(mLeftBlockElement));
+    // `WhiteSpaceVisibilityKeeper::
+    // MergeFirstLineOfRightBlockElementIntoDescendantLeftBlockElement()`
+    // returns ignored when:
+    // - No preceding invisible `<br>` element and
+    // - mNewListElementTagNameOfRightListElement is nothing and
+    // - There is no content to move from right block element.
+    if (!mPrecedingInvisibleBRElement) {
+      if (CanMergeLeftAndRightBlockElements()) {
+        // Always marked as handled in this case.
+        mFallbackToDeleteLeafContent = false;
+      } else {
+        // Marked as handled only when it actually moves a content node.
+        Result<bool, nsresult> firstLineHasContent =
+            AutoMoveOneLineHandler::CanMoveOrDeleteSomethingInLine(
+                mPointContainingTheOtherBlockElement
+                    .NextPoint<EditorDOMPoint>(),
+                aEditingHost);
+        mFallbackToDeleteLeafContent =
+            firstLineHasContent.isOk() && !firstLineHasContent.inspect();
+      }
+    } else {
+      // Marked as handled when deleting the invisible `<br>` element.
+      mFallbackToDeleteLeafContent = false;
+    }
+  } else if (mPointContainingTheOtherBlockElement.GetContainer() ==
+             mLeftBlockElement) {
+    mPrecedingInvisibleBRElement =
+        WSRunScanner::GetPrecedingBRElementUnlessVisibleContentFound(
+            aHTMLEditor.ComputeEditingHost(),
+            mPointContainingTheOtherBlockElement);
+    // `WhiteSpaceVisibilityKeeper::
+    // MergeFirstLineOfRightBlockElementIntoAncestorLeftBlockElement()`
+    // returns ignored when:
+    // - No preceding invisible `<br>` element and
+    // - mNewListElementTagNameOfRightListElement is some and
+    // - The right block element has no children
+    // or,
+    // - No preceding invisible `<br>` element and
+    // - mNewListElementTagNameOfRightListElement is nothing and
+    // - There is no content to move from right block element.
+    if (!mPrecedingInvisibleBRElement) {
+      if (CanMergeLeftAndRightBlockElements()) {
+        // Marked as handled only when it actualy moves a content node.
+        Result<bool, nsresult> rightBlockHasContent =
+            aHTMLEditor.CanMoveChildren(*mRightBlockElement,
+                                        *mLeftBlockElement);
+        mFallbackToDeleteLeafContent =
+            rightBlockHasContent.isOk() && !rightBlockHasContent.inspect();
+      } else {
+        // Marked as handled only when it actually moves a content node.
+        Result<bool, nsresult> firstLineHasContent =
+            AutoMoveOneLineHandler::CanMoveOrDeleteSomethingInLine(
+                EditorDOMPoint(mRightBlockElement, 0u), aEditingHost);
+        mFallbackToDeleteLeafContent =
+            firstLineHasContent.isOk() && !firstLineHasContent.inspect();
+      }
+    } else {
+      // Marked as handled when deleting the invisible `<br>` element.
+      mFallbackToDeleteLeafContent = false;
+    }
+  } else {
+    mPrecedingInvisibleBRElement =
+        WSRunScanner::GetPrecedingBRElementUnlessVisibleContentFound(
+            aHTMLEditor.ComputeEditingHost(),
+            EditorDOMPoint::AtEndOf(mLeftBlockElement));
+    // `WhiteSpaceVisibilityKeeper::
+    // MergeFirstLineOfRightBlockElementIntoLeftBlockElement()` always
+    // return "handled".
+    mFallbackToDeleteLeafContent = false;
+  }
+
+  mCanJoinBlocks = true;
+  return true;
+}
+
+nsresult HTMLEditor::AutoDeleteRangesHandler::AutoBlockElementsJoiner::
+    AutoInclusiveAncestorBlockElementsJoiner::ComputeRangesToDelete(
+        const HTMLEditor& aHTMLEditor, const EditorDOMPoint& aCaretPoint,
+        AutoRangeArray& aRangesToDelete) const {
+  MOZ_ASSERT(!aRangesToDelete.Ranges().IsEmpty());
+  MOZ_ASSERT(mLeftBlockElement);
+  MOZ_ASSERT(mRightBlockElement);
+
+  if (IsSameBlockElement()) {
+    if (!aCaretPoint.IsSet()) {
+      return NS_OK;  // The ranges are not collapsed, keep them as-is.
+    }
+    nsresult rv = aRangesToDelete.Collapse(aCaretPoint);
+    NS_WARNING_ASSERTION(NS_SUCCEEDED(rv), "AutoRangeArray::Collapse() failed");
+    return rv;
+  }
+
+  EditorDOMPoint pointContainingTheOtherBlock;
+  if (!EditorUtils::IsDescendantOf(*mLeftBlockElement, *mRightBlockElement,
+                                   &pointContainingTheOtherBlock)) {
+    Unused << EditorUtils::IsDescendantOf(
+        *mRightBlockElement, *mLeftBlockElement, &pointContainingTheOtherBlock);
+  }
+  EditorDOMRange range =
+      WSRunScanner::GetRangeForDeletingBlockElementBoundaries(
+          aHTMLEditor, *mLeftBlockElement, *mRightBlockElement,
+          pointContainingTheOtherBlock);
+  if (!range.IsPositioned()) {
+    NS_WARNING(
+        "WSRunScanner::GetRangeForDeletingBlockElementBoundaries() failed");
+    return NS_ERROR_FAILURE;
+  }
+  if (!aCaretPoint.IsSet()) {
+    // Don't shrink the original range.
+    bool noNeedToChangeStart = false;
+    const auto atStart =
+        aRangesToDelete.GetFirstRangeStartPoint<EditorDOMPoint>();
+    if (atStart.IsBefore(range.StartRef())) {
+      // If the range starts from end of a container, and computed block
+      // boundaries range starts from an invisible `<br>` element,  we
+      // may need to shrink the range.
+      Element* editingHost = aHTMLEditor.ComputeEditingHost();
+      NS_WARNING_ASSERTION(editingHost, "There was no editing host");
+      nsIContent* nextContent =
+          atStart.IsEndOfContainer() && range.StartRef().GetChild() &&
+                  HTMLEditUtils::IsInvisibleBRElement(
+                      *range.StartRef().GetChild())
+              ? HTMLEditUtils::GetNextContent(
+                    *atStart.ContainerAs<nsIContent>(),
+                    {WalkTreeOption::IgnoreDataNodeExceptText,
+                     WalkTreeOption::StopAtBlockBoundary},
+                    editingHost)
+              : nullptr;
+      if (!nextContent || nextContent != range.StartRef().GetChild()) {
+        noNeedToChangeStart = true;
+        range.SetStart(
+            aRangesToDelete.GetFirstRangeStartPoint<EditorDOMPoint>());
+      }
+    }
+    if (range.EndRef().IsBefore(
+            aRangesToDelete.GetFirstRangeEndPoint<EditorRawDOMPoint>())) {
+      if (noNeedToChangeStart) {
+        return NS_OK;  // We don't need to modify the range.
+      }
+      range.SetEnd(aRangesToDelete.GetFirstRangeEndPoint<EditorDOMPoint>());
+    }
+  }
+  // XXX Oddly, we join blocks only at the first range.
+  nsresult rv = aRangesToDelete.FirstRangeRef()->SetStartAndEnd(
+      range.StartRef().ToRawRangeBoundary(),
+      range.EndRef().ToRawRangeBoundary());
+  NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                       "AutoRangeArray::SetStartAndEnd() failed");
+  return rv;
+}
+
+Result<EditActionResult, nsresult> HTMLEditor::AutoDeleteRangesHandler::
+    AutoBlockElementsJoiner::AutoInclusiveAncestorBlockElementsJoiner::Run(
+        HTMLEditor& aHTMLEditor, const Element& aEditingHost) {
+  MOZ_ASSERT(aHTMLEditor.IsEditActionDataAvailable());
+  MOZ_ASSERT(mLeftBlockElement);
+  MOZ_ASSERT(mRightBlockElement);
+
+  if (IsSameBlockElement()) {
+    return EditActionResult::IgnoredResult();
+  }
+
+  if (!mCanJoinBlocks) {
+    return EditActionResult::HandledResult();
+  }
+
+  EditorDOMPoint startOfRightContent;
+
+  // If the left block element is in the right block element, move the hard
+  // line including the right block element to end of the left block.
+  // However, if we are merging list elements, we don't join them.
+  Result<EditActionResult, nsresult> result(NS_ERROR_NOT_INITIALIZED);
+  if (mPointContainingTheOtherBlockElement.GetContainer() ==
+      mRightBlockElement) {
+    startOfRightContent = mPointContainingTheOtherBlockElement.NextPoint();
+    if (Element* element = startOfRightContent.GetChildAs<Element>()) {
+      startOfRightContent =
+          HTMLEditUtils::GetDeepestEditableStartPointOf<EditorDOMPoint>(
+              *element);
+    }
+    AutoTrackDOMPoint trackStartOfRightBlock(aHTMLEditor.RangeUpdaterRef(),
+                                             &startOfRightContent);
+    result = WhiteSpaceVisibilityKeeper::
+        MergeFirstLineOfRightBlockElementIntoDescendantLeftBlockElement(
+            aHTMLEditor, MOZ_KnownLive(*mLeftBlockElement),
+            MOZ_KnownLive(*mRightBlockElement),
+            mPointContainingTheOtherBlockElement,
+            mNewListElementTagNameOfRightListElement,
+            MOZ_KnownLive(mPrecedingInvisibleBRElement), aEditingHost);
+    if (MOZ_UNLIKELY(result.isErr())) {
+      NS_WARNING(
+          "WhiteSpaceVisibilityKeeper::"
+          "MergeFirstLineOfRightBlockElementIntoDescendantLeftBlockElement() "
+          "failed");
+      return result;
+    }
+    if (NS_WARN_IF(!startOfRightContent.IsSet()) ||
+        NS_WARN_IF(!startOfRightContent.GetContainer()->IsInComposedDoc())) {
+      return Err(NS_ERROR_EDITOR_UNEXPECTED_DOM_TREE);
+    }
+  }
+
+  // If the right block element is in the left block element:
+  // - move list item elements in the right block element to where the left
+  //   list element is
+  // - or first hard line in the right block element to where:
+  //   - the left block element is.
+  //   - or the given left content in the left block is.
+  else if (mPointContainingTheOtherBlockElement.GetContainer() ==
+           mLeftBlockElement) {
+    startOfRightContent =
+        HTMLEditUtils::GetDeepestEditableStartPointOf<EditorDOMPoint>(
+            *mRightBlockElement);
+    AutoTrackDOMPoint trackStartOfRightBlock(aHTMLEditor.RangeUpdaterRef(),
+                                             &startOfRightContent);
+    result = WhiteSpaceVisibilityKeeper::
+        MergeFirstLineOfRightBlockElementIntoAncestorLeftBlockElement(
+            aHTMLEditor, MOZ_KnownLive(*mLeftBlockElement),
+            MOZ_KnownLive(*mRightBlockElement),
+            mPointContainingTheOtherBlockElement,
+            MOZ_KnownLive(*mInclusiveDescendantOfLeftBlockElement),
+            mNewListElementTagNameOfRightListElement,
+            MOZ_KnownLive(mPrecedingInvisibleBRElement), aEditingHost);
+    if (MOZ_UNLIKELY(result.isErr())) {
+      NS_WARNING(
+          "WhiteSpaceVisibilityKeeper::"
+          "MergeFirstLineOfRightBlockElementIntoAncestorLeftBlockElement() "
+          "failed");
+      return result;
+    }
+    trackStartOfRightBlock.FlushAndStopTracking();
+    if (NS_WARN_IF(!startOfRightContent.IsSet()) ||
+        NS_WARN_IF(!startOfRightContent.GetContainer()->IsInComposedDoc())) {
+      return Err(NS_ERROR_EDITOR_UNEXPECTED_DOM_TREE);
+    }
+
+  }
+
+  // Normal case.  Blocks are siblings, or at least close enough.  An example
+  // of the latter is <p>paragraph</p><ul><li>one<li>two<li>three</ul>.  The
+  // first li and the p are not true siblings, but we still want to join them
+  // if you backspace from li into p.
+  else {
+    MOZ_ASSERT(!mPointContainingTheOtherBlockElement.IsSet());
+
+    startOfRightContent =
+        HTMLEditUtils::GetDeepestEditableStartPointOf<EditorDOMPoint>(
+            *mRightBlockElement);
+    AutoTrackDOMPoint trackStartOfRightBlock(aHTMLEditor.RangeUpdaterRef(),
+                                             &startOfRightContent);
+    result = WhiteSpaceVisibilityKeeper::
+        MergeFirstLineOfRightBlockElementIntoLeftBlockElement(
+            aHTMLEditor, MOZ_KnownLive(*mLeftBlockElement),
+            MOZ_KnownLive(*mRightBlockElement),
+            mNewListElementTagNameOfRightListElement,
+            MOZ_KnownLive(mPrecedingInvisibleBRElement), aEditingHost);
+    if (MOZ_UNLIKELY(result.isErr())) {
+      NS_WARNING(
+          "WhiteSpaceVisibilityKeeper::"
+          "MergeFirstLineOfRightBlockElementIntoLeftBlockElement() failed");
+      return result;
+    }
+    trackStartOfRightBlock.FlushAndStopTracking();
+    if (NS_WARN_IF(!startOfRightContent.IsSet()) ||
+        NS_WARN_IF(!startOfRightContent.GetContainer()->IsInComposedDoc())) {
+      return Err(NS_ERROR_EDITOR_UNEXPECTED_DOM_TREE);
+    }
+  }
+
+  // If we're deleting selection (meaning not replacing selection with new
+  // content), we should put caret to end of preceding text node if there is.
+  // Then, users can type text into it like the other browsers.
+  if (MayEditActionDeleteAroundCollapsedSelection(
+          aHTMLEditor.GetEditAction())) {
+    WSRunScanner scanner(&aEditingHost, startOfRightContent);
+    WSScanResult maybePreviousText =
+        scanner.ScanPreviousVisibleNodeOrBlockBoundaryFrom(startOfRightContent);
+    if (maybePreviousText.IsContentEditable() &&
+        maybePreviousText.InVisibleOrCollapsibleCharacters()) {
+      mPointToPutCaret = maybePreviousText.Point<EditorDOMPoint>();
+    }
+  }
+  return result;
+}
+
+// static
+Result<bool, nsresult>
+HTMLEditor::AutoMoveOneLineHandler::CanMoveOrDeleteSomethingInLine(
+    const EditorDOMPoint& aPointInHardLine, const Element& aEditingHost) {
+  if (NS_WARN_IF(!aPointInHardLine.IsSet()) ||
+      NS_WARN_IF(aPointInHardLine.IsInNativeAnonymousSubtree())) {
+    return Err(NS_ERROR_INVALID_ARG);
+  }
+
+  RefPtr<nsRange> oneLineRange =
+      AutoRangeArray::CreateRangeWrappingStartAndEndLinesContainingBoundaries(
+          aPointInHardLine, aPointInHardLine,
+          EditSubAction::eMergeBlockContents, aEditingHost);
+  if (!oneLineRange || oneLineRange->Collapsed() ||
+      !oneLineRange->IsPositioned() ||
+      !oneLineRange->GetStartContainer()->IsContent() ||
+      !oneLineRange->GetEndContainer()->IsContent()) {
+    return false;
+  }
+
+  // If there is only a padding `<br>` element in a empty block, it's selected
+  // by `UpdatePointsToSelectAllChildrenIfCollapsedInEmptyBlockElement()`.
+  // However, it won't be moved.  Although it'll be deleted,
+  // AutoMoveOneLineHandler returns "ignored".  Therefore, we should return
+  // `false` in this case.
+  if (nsIContent* childContent = oneLineRange->GetChildAtStartOffset()) {
+    if (childContent->IsHTMLElement(nsGkAtoms::br) &&
+        childContent->GetParent()) {
+      if (const Element* blockElement =
+              HTMLEditUtils::GetInclusiveAncestorElement(
+                  *childContent->GetParent(),
+                  HTMLEditUtils::ClosestBlockElement)) {
+        if (HTMLEditUtils::IsEmptyNode(*blockElement)) {
+          return false;
+        }
+      }
+    }
+  }
+
+  nsINode* commonAncestor = oneLineRange->GetClosestCommonInclusiveAncestor();
+  // Currently, we move non-editable content nodes too.
+  EditorRawDOMPoint startPoint(oneLineRange->StartRef());
+  if (!startPoint.IsEndOfContainer()) {
+    return true;
+  }
+  EditorRawDOMPoint endPoint(oneLineRange->EndRef());
+  if (!endPoint.IsStartOfContainer()) {
+    return true;
+  }
+  if (startPoint.GetContainer() != commonAncestor) {
+    while (true) {
+      EditorRawDOMPoint pointInParent(startPoint.GetContainerAs<nsIContent>());
+      if (NS_WARN_IF(!pointInParent.IsInContentNode())) {
+        return Err(NS_ERROR_FAILURE);
+      }
+      if (pointInParent.GetContainer() == commonAncestor) {
+        startPoint = pointInParent;
+        break;
+      }
+      if (!pointInParent.IsEndOfContainer()) {
+        return true;
+      }
+    }
+  }
+  if (endPoint.GetContainer() != commonAncestor) {
+    while (true) {
+      EditorRawDOMPoint pointInParent(endPoint.GetContainerAs<nsIContent>());
+      if (NS_WARN_IF(!pointInParent.IsInContentNode())) {
+        return Err(NS_ERROR_FAILURE);
+      }
+      if (pointInParent.GetContainer() == commonAncestor) {
+        endPoint = pointInParent;
+        break;
+      }
+      if (!pointInParent.IsStartOfContainer()) {
+        return true;
+      }
+    }
+  }
+  // If start point and end point in the common ancestor are direct siblings,
+  // there is no content to move or delete.
+  // E.g., `<b>abc<br>[</b><i>]<br>def</i>`.
+  return startPoint.GetNextSiblingOfChild() != endPoint.GetChild();
+}
+
+nsresult HTMLEditor::AutoMoveOneLineHandler::Prepare(
+    HTMLEditor& aHTMLEditor, const EditorDOMPoint& aPointInHardLine,
+    const Element& aEditingHost) {
+  MOZ_ASSERT(aHTMLEditor.IsEditActionDataAvailable());
+  MOZ_ASSERT(aPointInHardLine.IsInContentNode());
+  MOZ_ASSERT(mPointToInsert.IsSetAndValid());
+
+  if (NS_WARN_IF(mPointToInsert.IsInNativeAnonymousSubtree())) {
+    return Err(NS_ERROR_INVALID_ARG);
+  }
+
+  mSrcInclusiveAncestorBlock =
+      aPointInHardLine.IsInContentNode()
+          ? HTMLEditUtils::GetInclusiveAncestorElement(
+                *aPointInHardLine.ContainerAs<nsIContent>(),
+                HTMLEditUtils::ClosestBlockElement)
+          : nullptr;
+  mDestInclusiveAncestorBlock =
+      mPointToInsert.IsInContentNode()
+          ? HTMLEditUtils::GetInclusiveAncestorElement(
+                *mPointToInsert.ContainerAs<nsIContent>(),
+                HTMLEditUtils::ClosestBlockElement)
+          : nullptr;
+  mMovingToParentBlock =
+      mDestInclusiveAncestorBlock && mSrcInclusiveAncestorBlock &&
+      mDestInclusiveAncestorBlock != mSrcInclusiveAncestorBlock &&
+      mSrcInclusiveAncestorBlock->IsInclusiveDescendantOf(
+          mDestInclusiveAncestorBlock);
+  mTopmostSrcAncestorBlockInDestBlock =
+      mMovingToParentBlock
+          ? AutoMoveOneLineHandler::
+                GetMostDistantInclusiveAncestorBlockInSpecificAncestorElement(
+                    *mSrcInclusiveAncestorBlock, *mDestInclusiveAncestorBlock)
+          : nullptr;
+  MOZ_ASSERT_IF(mMovingToParentBlock, mTopmostSrcAncestorBlockInDestBlock);
+
+  mPreserveWhiteSpaceStyle =
+      AutoMoveOneLineHandler::ConsiderWhetherPreserveWhiteSpaceStyle(
+          aPointInHardLine.GetContainerAs<nsIContent>(),
+          mDestInclusiveAncestorBlock);
+
+  AutoRangeArray rangesToWrapTheLine(aPointInHardLine);
+  rangesToWrapTheLine.ExtendRangesToWrapLinesToHandleBlockLevelEditAction(
+      EditSubAction::eMergeBlockContents, aEditingHost);
+  MOZ_ASSERT(rangesToWrapTheLine.Ranges().Length() <= 1u);
+  mLineRange = EditorDOMRange(rangesToWrapTheLine.FirstRangeRef());
+  return NS_OK;
+}
+
+Result<CaretPoint, nsresult>
+HTMLEditor::AutoMoveOneLineHandler::SplitToMakeTheLineIsolated(
+    HTMLEditor& aHTMLEditor, const nsIContent& aNewContainer,
+    const Element& aEditingHost,
+    nsTArray<OwningNonNull<nsIContent>>& aOutArrayOfContents) const {
+  AutoRangeArray rangesToWrapTheLine(mLineRange);
+  Result<EditorDOMPoint, nsresult> splitResult =
+      rangesToWrapTheLine
+          .SplitTextAtEndBoundariesAndInlineAncestorsAtBothBoundaries(
+              aHTMLEditor, aEditingHost, &aNewContainer);
+  if (MOZ_UNLIKELY(splitResult.isErr())) {
+    NS_WARNING(
+        "AutoRangeArray::"
+        "SplitTextAtEndBoundariesAndInlineAncestorsAtBothBoundaries() failed");
+    return Err(splitResult.unwrapErr());
+  }
+  EditorDOMPoint pointToPutCaret;
+  if (splitResult.inspect().IsSet()) {
+    pointToPutCaret = splitResult.unwrap();
+  }
+  nsresult rv = rangesToWrapTheLine.CollectEditTargetNodes(
+      aHTMLEditor, aOutArrayOfContents, EditSubAction::eMergeBlockContents,
+      AutoRangeArray::CollectNonEditableNodes::Yes);
+  if (NS_FAILED(rv)) {
+    NS_WARNING(
+        "AutoRangeArray::CollectEditTargetNodes(EditSubAction::"
+        "eMergeBlockContents, CollectNonEditableNodes::Yes) failed");
+    return Err(rv);
+  }
+  return CaretPoint(pointToPutCaret);
+}
+
+// static
+Element* HTMLEditor::AutoMoveOneLineHandler::
+    GetMostDistantInclusiveAncestorBlockInSpecificAncestorElement(
+        Element& aBlockElement, const Element& aAncestorElement) {
+  MOZ_ASSERT(aBlockElement.IsInclusiveDescendantOf(&aAncestorElement));
+  MOZ_ASSERT(HTMLEditUtils::IsBlockElement(aBlockElement));
+
+  if (&aBlockElement == &aAncestorElement) {
+    return nullptr;
+  }
+
+  Element* lastBlockAncestor = &aBlockElement;
+  for (Element* element : aBlockElement.InclusiveAncestorsOfType<Element>()) {
+    if (element == &aAncestorElement) {
+      return lastBlockAncestor;
+    }
+    if (HTMLEditUtils::IsBlockElement(*lastBlockAncestor)) {
+      lastBlockAncestor = element;
+    }
+  }
+  return nullptr;
+}
+
+// static
+HTMLEditor::PreserveWhiteSpaceStyle
+HTMLEditor::AutoMoveOneLineHandler::ConsiderWhetherPreserveWhiteSpaceStyle(
+    const nsIContent* aContentInLine,
+    const Element* aInclusiveAncestorBlockOfInsertionPoint) {
+  if (MOZ_UNLIKELY(!aInclusiveAncestorBlockOfInsertionPoint)) {
+    return PreserveWhiteSpaceStyle::No;
+  }
+
+  // If we move content from or to <pre>, we don't need to preserve the
+  // white-space style for compatibility with both our traditional behavior
+  // and the other browsers.
+
+  // TODO: If `white-space` is specified by non-UA stylesheet, we should
+  // preserve it even if the right block is <pre> for compatibility with the
+  // other browsers.
+  const auto IsInclusiveDescendantOfPre = [](const nsIContent& aContent) {
+    // If the content has different `white-space` style from <pre>, we
+    // shouldn't treat it as a descendant of <pre> because web apps or
+    // the user intent to treat the white-spaces in aContent not as `pre`.
+    if (EditorUtils::GetComputedWhiteSpaceStyle(aContent).valueOr(
+            StyleWhiteSpace::Normal) != StyleWhiteSpace::Pre) {
+      return false;
+    }
+    for (const Element* element :
+         aContent.InclusiveAncestorsOfType<Element>()) {
+      if (element->IsHTMLElement(nsGkAtoms::pre)) {
+        return true;
+      }
+    }
+    return false;
+  };
+  if (IsInclusiveDescendantOfPre(*aInclusiveAncestorBlockOfInsertionPoint) ||
+      MOZ_UNLIKELY(!aContentInLine) ||
+      IsInclusiveDescendantOfPre(*aContentInLine)) {
+    return PreserveWhiteSpaceStyle::No;
+  }
+  return PreserveWhiteSpaceStyle::Yes;
+}
+
+Result<MoveNodeResult, nsresult> HTMLEditor::AutoMoveOneLineHandler::Run(
+    HTMLEditor& aHTMLEditor, const Element& aEditingHost) {
+  EditorDOMPoint pointToInsert(NextInsertionPointRef());
+  MOZ_ASSERT(pointToInsert.IsInContentNode());
+
+  EditorDOMPoint pointToPutCaret;
+  AutoTArray<OwningNonNull<nsIContent>, 64> arrayOfContents;
+  {
+    AutoTrackDOMPoint tackPointToInsert(aHTMLEditor.RangeUpdaterRef(),
+                                        &pointToInsert);
+
+    Result<CaretPoint, nsresult> splitAtLineEdgesResult =
+        SplitToMakeTheLineIsolated(
+            aHTMLEditor,
+            MOZ_KnownLive(*pointToInsert.ContainerAs<nsIContent>()),
+            aEditingHost, arrayOfContents);
+    if (MOZ_UNLIKELY(splitAtLineEdgesResult.isErr())) {
+      NS_WARNING("AutoMoveOneLineHandler::SplitToMakeTheLineIsolated() failed");
+      return splitAtLineEdgesResult.propagateErr();
+    }
+    splitAtLineEdgesResult.unwrap().MoveCaretPointTo(
+        pointToPutCaret, {SuggestCaret::OnlyIfHasSuggestion});
+
+    Result<EditorDOMPoint, nsresult> splitAtBRElementsResult =
+        aHTMLEditor.MaybeSplitElementsAtEveryBRElement(
+            arrayOfContents, EditSubAction::eMergeBlockContents);
+    if (MOZ_UNLIKELY(splitAtBRElementsResult.isErr())) {
+      NS_WARNING(
+          "HTMLEditor::MaybeSplitElementsAtEveryBRElement(EditSubAction::"
+          "eMergeBlockContents) failed");
+      return splitAtBRElementsResult.propagateErr();
+    }
+    if (splitAtBRElementsResult.inspect().IsSet()) {
+      pointToPutCaret = splitAtBRElementsResult.unwrap();
+    }
+  }
+
+  if (!pointToInsert.IsSetAndValid()) {
+    return Err(NS_ERROR_EDITOR_UNEXPECTED_DOM_TREE);
+  }
+
+  if (aHTMLEditor.AllowsTransactionsToChangeSelection() &&
+      pointToPutCaret.IsSet()) {
+    nsresult rv = aHTMLEditor.CollapseSelectionTo(pointToPutCaret);
+    if (NS_FAILED(rv)) {
+      NS_WARNING("EditorBase::CollapseSelectionTo() failed");
+      return Err(rv);
+    }
+  }
+
+  if (arrayOfContents.IsEmpty()) {
+    return MoveNodeResult::IgnoredResult(std::move(pointToInsert));
+  }
+
+  // Track the range which contains the moved contents.
+  if (ForceMoveToEndOfContainer()) {
+    pointToInsert = NextInsertionPointRef();
+  }
+  EditorDOMRange movedContentRange(pointToInsert);
+  MoveNodeResult moveContentsInLineResult =
+      MoveNodeResult::IgnoredResult(pointToInsert);
+  for (const OwningNonNull<nsIContent>& content : arrayOfContents) {
+    {
+      AutoEditorDOMRangeChildrenInvalidator lockOffsets(movedContentRange);
+      // If the content is a block element, move all children of it to the
+      // new container, and then, remove the (probably) empty block element.
+      if (HTMLEditUtils::IsBlockElement(content)) {
+        Result<MoveNodeResult, nsresult> moveChildrenResult =
+            aHTMLEditor.MoveChildrenWithTransaction(
+                MOZ_KnownLive(*content->AsElement()), pointToInsert,
+                mPreserveWhiteSpaceStyle, RemoveIfCommentNode::Yes);
+        if (MOZ_UNLIKELY(moveChildrenResult.isErr())) {
+          NS_WARNING("HTMLEditor::MoveChildrenWithTransaction() failed");
+          moveContentsInLineResult.IgnoreCaretPointSuggestion();
+          return moveChildrenResult;
+        }
+        moveContentsInLineResult |= moveChildrenResult.inspect();
+        moveContentsInLineResult.MarkAsHandled();
+        // MOZ_KnownLive due to bug 1620312
+        nsresult rv =
+            aHTMLEditor.DeleteNodeWithTransaction(MOZ_KnownLive(content));
+        if (NS_WARN_IF(rv == NS_ERROR_EDITOR_DESTROYED)) {
+          moveContentsInLineResult.IgnoreCaretPointSuggestion();
+          return Err(NS_ERROR_EDITOR_DESTROYED);
+        }
+        NS_WARNING_ASSERTION(
+            NS_SUCCEEDED(rv),
+            "EditorBase::DeleteNodeWithTransaction() failed, but ignored");
+      }
+      // If the moving content is a comment node or an empty inline node, we
+      // don't want it to appear in the dist paragraph.
+      else if (content->IsComment() ||
+               HTMLEditUtils::IsEmptyInlineContainer(
+                   content, {EmptyCheckOption::TreatSingleBRElementAsVisible,
+                             EmptyCheckOption::TreatListItemAsVisible,
+                             EmptyCheckOption::TreatTableCellAsVisible})) {
+        nsCOMPtr<nsIContent> emptyContent =
+            HTMLEditUtils::GetMostDistantAncestorEditableEmptyInlineElement(
+                content, &aEditingHost,
+                pointToInsert.ContainerAs<nsIContent>());
+        if (!emptyContent) {
+          emptyContent = content;
+        }
+        nsresult rv = aHTMLEditor.DeleteNodeWithTransaction(*emptyContent);
+        if (NS_FAILED(rv)) {
+          NS_WARNING("EditorBase::DeleteNodeWithTransaction() failed");
+          moveContentsInLineResult.IgnoreCaretPointSuggestion();
+          return Err(rv);
+        }
+      } else {
+        // MOZ_KnownLive due to bug 1620312
+        Result<MoveNodeResult, nsresult> moveNodeOrChildrenResult =
+            aHTMLEditor.MoveNodeOrChildrenWithTransaction(
+                MOZ_KnownLive(content), pointToInsert, mPreserveWhiteSpaceStyle,
+                RemoveIfCommentNode::Yes);
+        if (MOZ_UNLIKELY(moveNodeOrChildrenResult.isErr())) {
+          NS_WARNING("HTMLEditor::MoveNodeOrChildrenWithTransaction() failed");
+          moveContentsInLineResult.IgnoreCaretPointSuggestion();
+          return moveNodeOrChildrenResult;
+        }
+        moveContentsInLineResult |= moveNodeOrChildrenResult.inspect();
+      }
+    }
+    // For backward compatibility, we should move contents to end of the
+    // container if the instance is created without specific insertion point.
+    if (ForceMoveToEndOfContainer()) {
+      pointToInsert = NextInsertionPointRef();
+      movedContentRange.SetEnd(pointToInsert);
+    }
+    // And also if pointToInsert has been made invalid with removing preceding
+    // children, we should move the content to the end of the container.
+    else if (aHTMLEditor.MayHaveMutationEventListeners() &&
+             MOZ_UNLIKELY(!moveContentsInLineResult.NextInsertionPointRef()
+                               .IsSetAndValid())) {
+      mPointToInsert.SetToEndOf(mPointToInsert.GetContainer());
+      pointToInsert = NextInsertionPointRef();
+      movedContentRange.SetEnd(pointToInsert);
+    } else {
+      MOZ_DIAGNOSTIC_ASSERT(
+          moveContentsInLineResult.NextInsertionPointRef().IsSet());
+      mPointToInsert = moveContentsInLineResult.NextInsertionPointRef();
+      pointToInsert = NextInsertionPointRef();
+      if (!aHTMLEditor.MayHaveMutationEventListeners() ||
+          movedContentRange.EndRef().IsBefore(pointToInsert)) {
+        movedContentRange.SetEnd(pointToInsert);
+      }
+    }
+  }
+
+  // Nothing has been moved, we don't need to clean up unnecessary <br> element.
+  // And also if we're not moving content into a block, we can quit right now.
+  if (moveContentsInLineResult.Ignored() ||
+      MOZ_UNLIKELY(!mDestInclusiveAncestorBlock)) {
+    return moveContentsInLineResult;
+  }
+
+  // If we couldn't track the range to clean up, we should just stop cleaning up
+  // because returning error from here may change the behavior of web apps using
+  // mutation event listeners.
+  if (MOZ_UNLIKELY(!movedContentRange.IsPositioned() ||
+                   movedContentRange.Collapsed())) {
+    return moveContentsInLineResult;
+  }
+
+  nsresult rv = DeleteUnnecessaryTrailingLineBreakInMovedLineEnd(
+      aHTMLEditor, movedContentRange, aEditingHost);
+  if (NS_FAILED(rv)) {
+    NS_WARNING(
+        "AutoMoveOneLineHandler::"
+        "DeleteUnnecessaryTrailingLineBreakInMovedLineEnd() failed");
+    moveContentsInLineResult.IgnoreCaretPointSuggestion();
+    return Err(rv);
+  }
+  return moveContentsInLineResult;
+}
+
+nsresult HTMLEditor::AutoMoveOneLineHandler::
+    DeleteUnnecessaryTrailingLineBreakInMovedLineEnd(
+        HTMLEditor& aHTMLEditor, const EditorDOMRange& aMovedContentRange,
+        const Element& aEditingHost) const {
+  MOZ_ASSERT(mDestInclusiveAncestorBlock);
+  MOZ_ASSERT(aMovedContentRange.IsPositioned());
+  MOZ_ASSERT(!aMovedContentRange.Collapsed());
+
+  // If we didn't preserve white-space for backward compatibility and
+  // white-space becomes not preformatted, we need to clean it up the last text
+  // node if it ends with a preformatted line break.
+  if (mPreserveWhiteSpaceStyle == PreserveWhiteSpaceStyle::No) {
+    const RefPtr<Text> textNodeEndingWithUnnecessaryLineBreak = [&]() -> Text* {
+      Text* lastTextNode = Text::FromNodeOrNull(
+          mMovingToParentBlock
+              ? HTMLEditUtils::GetPreviousContent(
+                    *mTopmostSrcAncestorBlockInDestBlock,
+                    {WalkTreeOption::StopAtBlockBoundary},
+                    mDestInclusiveAncestorBlock)
+              : HTMLEditUtils::GetLastLeafContent(
+                    *mDestInclusiveAncestorBlock,
+                    {LeafNodeType::LeafNodeOrNonEditableNode}));
+      if (!lastTextNode ||
+          !HTMLEditUtils::IsSimplyEditableNode(*lastTextNode)) {
+        return nullptr;
+      }
+      const nsTextFragment& textFragment = lastTextNode->TextFragment();
+      const char16_t lastCh =
+          textFragment.GetLength()
+              ? textFragment.CharAt(textFragment.GetLength() - 1u)
+              : 0;
+      return lastCh == HTMLEditUtils::kNewLine &&
+                     !EditorUtils::IsNewLinePreformatted(*lastTextNode)
+                 ? lastTextNode
+                 : nullptr;
+    }();
+    if (textNodeEndingWithUnnecessaryLineBreak) {
+      if (textNodeEndingWithUnnecessaryLineBreak->TextDataLength() == 1u) {
+        const RefPtr<Element> inlineElement =
+            HTMLEditUtils::GetMostDistantAncestorEditableEmptyInlineElement(
+                *textNodeEndingWithUnnecessaryLineBreak, &aEditingHost);
+        nsresult rv = aHTMLEditor.DeleteNodeWithTransaction(
+            inlineElement ? static_cast<nsIContent&>(*inlineElement)
+                          : static_cast<nsIContent&>(
+                                *textNodeEndingWithUnnecessaryLineBreak));
+        if (NS_FAILED(rv)) {
+          NS_WARNING("EditorBase::DeleteNodeWithTransaction() failed");
+          return Err(rv);
+        }
+      } else {
+        Result<CaretPoint, nsresult> caretPointOrError =
+            aHTMLEditor.DeleteTextWithTransaction(
+                *textNodeEndingWithUnnecessaryLineBreak,
+                textNodeEndingWithUnnecessaryLineBreak->TextDataLength() - 1u,
+                1u);
+        if (MOZ_UNLIKELY(caretPointOrError.isErr())) {
+          NS_WARNING("HTMLEditor::DeleteTextWithTransaction() failed");
+          return caretPointOrError.propagateErr();
+        }
+        nsresult rv = caretPointOrError.inspect().SuggestCaretPointTo(
+            aHTMLEditor, {SuggestCaret::OnlyIfHasSuggestion,
+                          SuggestCaret::OnlyIfTransactionsAllowedToDoIt,
+                          SuggestCaret::AndIgnoreTrivialError});
+        if (NS_FAILED(rv)) {
+          NS_WARNING("CaretPoint::SuggestCaretPointTo() failed");
+          return Err(rv);
+        }
+        NS_WARNING_ASSERTION(
+            rv != NS_SUCCESS_EDITOR_BUT_IGNORED_TRIVIAL_ERROR,
+            "CaretPoint::SuggestCaretPointTo() failed, but ignored");
+      }
+    }
+  }
+
+  nsCOMPtr<nsIContent> lastLineBreakContent =
+      mMovingToParentBlock
+          ? HTMLEditUtils::GetUnnecessaryLineBreakContent(
+                *mTopmostSrcAncestorBlockInDestBlock,
+                ScanLineBreak::BeforeBlock)
+          : HTMLEditUtils::GetUnnecessaryLineBreakContent(
+                *mDestInclusiveAncestorBlock, ScanLineBreak::AtEndOfBlock);
+  if (!lastLineBreakContent) {
+    return NS_OK;
+  }
+  EditorRawDOMPoint atUnnecessaryLineBreak(lastLineBreakContent);
+  if (NS_WARN_IF(!atUnnecessaryLineBreak.IsSet())) {
+    return NS_ERROR_FAILURE;
+  }
+  // If the found unnecessary line break is not what we moved above, we
+  // shouldn't remove it.  E.g., the web app may have inserted it intentionally.
+  MOZ_ASSERT(aMovedContentRange.StartRef().IsSetAndValid());
+  MOZ_ASSERT(aMovedContentRange.EndRef().IsSetAndValid());
+  if (!aMovedContentRange.Contains(atUnnecessaryLineBreak)) {
+    return NS_OK;
+  }
+
+  AutoTransactionsConserveSelection dontChangeMySelection(aHTMLEditor);
+  // If it's a text node and ending with a preformatted line break, we should
+  // delete it.
+  if (Text* textNode = Text::FromNode(lastLineBreakContent)) {
+    MOZ_ASSERT(EditorUtils::IsNewLinePreformatted(*textNode));
+    if (textNode->TextDataLength() > 1) {
+      Result<CaretPoint, nsresult> caretPointOrError =
+          aHTMLEditor.DeleteTextWithTransaction(
+              MOZ_KnownLive(*textNode), textNode->TextDataLength() - 1u, 1u);
+      if (MOZ_UNLIKELY(caretPointOrError.isErr())) {
+        NS_WARNING("HTMLEditor::DeleteTextWithTransaction() failed");
+        return caretPointOrError.unwrapErr();
+      }
+      // IgnoreCaretPointSuggestion() because of dontChangeMySelection above.
+      caretPointOrError.unwrap().IgnoreCaretPointSuggestion();
+      return NS_OK;
+    }
+  } else {
+    MOZ_ASSERT(lastLineBreakContent->IsHTMLElement(nsGkAtoms::br));
+  }
+  // If last line break content is the only content of its inline parent, we
+  // should remove the parent too.
+  if (const RefPtr<Element> inlineElement =
+          HTMLEditUtils::GetMostDistantAncestorEditableEmptyInlineElement(
+              *lastLineBreakContent, &aEditingHost)) {
+    nsresult rv = aHTMLEditor.DeleteNodeWithTransaction(*inlineElement);
+    NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                         "EditorBase::DeleteNodeWithTransaction() failed");
+    return rv;
+  }
+  // Or if the text node has only the preformatted line break or <br> element,
+  // we should remove it.
+  nsresult rv = aHTMLEditor.DeleteNodeWithTransaction(*lastLineBreakContent);
+  NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                       "EditorBase::DeleteNodeWithTransaction() failed");
+  return rv;
+}
+
+Result<bool, nsresult> HTMLEditor::CanMoveNodeOrChildren(
+    const nsIContent& aContent, const nsINode& aNewContainer) const {
+  if (HTMLEditUtils::CanNodeContain(aNewContainer, aContent)) {
+    return true;
+  }
+  if (aContent.IsElement()) {
+    return CanMoveChildren(*aContent.AsElement(), aNewContainer);
+  }
+  return true;
+}
+
+Result<MoveNodeResult, nsresult> HTMLEditor::MoveNodeOrChildrenWithTransaction(
+    nsIContent& aContentToMove, const EditorDOMPoint& aPointToInsert,
+    PreserveWhiteSpaceStyle aPreserveWhiteSpaceStyle,
+    RemoveIfCommentNode aRemoveIfCommentNode) {
+  MOZ_ASSERT(IsEditActionDataAvailable());
+  MOZ_ASSERT(aPointToInsert.IsInContentNode());
+
+  const auto destWhiteSpaceStyle = [&]() -> Maybe<StyleWhiteSpace> {
+    if (aPreserveWhiteSpaceStyle == PreserveWhiteSpaceStyle::No ||
+        !aPointToInsert.IsInContentNode()) {
+      return Nothing();
+    }
+    auto style = EditorUtils::GetComputedWhiteSpaceStyle(
+        *aPointToInsert.ContainerAs<nsIContent>());
+    if (NS_WARN_IF(style.isSome() &&
+                   style.value() == StyleWhiteSpace::PreSpace)) {
+      return Nothing();
+    }
+    return style;
+  }();
+  const auto srcWhiteSpaceStyle = [&]() -> Maybe<StyleWhiteSpace> {
+    if (aPreserveWhiteSpaceStyle == PreserveWhiteSpaceStyle::No) {
+      return Nothing();
+    }
+    auto style = EditorUtils::GetComputedWhiteSpaceStyle(aContentToMove);
+    if (NS_WARN_IF(style.isSome() &&
+                   style.value() == StyleWhiteSpace::PreSpace)) {
+      return Nothing();
+    }
+    return style;
+  }();
+  const auto GetWhiteSpaceStyleValue = [](StyleWhiteSpace aStyleWhiteSpace) {
+    switch (aStyleWhiteSpace) {
+      case StyleWhiteSpace::Normal:
+        return u"normal"_ns;
+      case StyleWhiteSpace::Pre:
+        return u"pre"_ns;
+      case StyleWhiteSpace::Nowrap:
+        return u"nowrap"_ns;
+      case StyleWhiteSpace::PreWrap:
+        return u"pre-wrap"_ns;
+      case StyleWhiteSpace::PreLine:
+        return u"pre-line"_ns;
+      case StyleWhiteSpace::BreakSpaces:
+        return u"break-spaces"_ns;
+      case StyleWhiteSpace::PreSpace:
+        MOZ_ASSERT_UNREACHABLE("Don't handle -moz-pre-space");
+        return u""_ns;
+      default:
+        MOZ_ASSERT_UNREACHABLE("Handle the new white-space value");
+        return u""_ns;
+    }
+  };
+
+  if (aRemoveIfCommentNode == RemoveIfCommentNode::Yes &&
+      aContentToMove.IsComment()) {
+    EditorDOMPoint pointToInsert(aPointToInsert);
+    {
+      AutoTrackDOMPoint trackPointToInsert(RangeUpdaterRef(), &pointToInsert);
+      nsresult rv = DeleteNodeWithTransaction(aContentToMove);
+      if (NS_FAILED(rv)) {
+        NS_WARNING("EditorBase::DeleteNodeWithTransaction() failed");
+        return Err(rv);
+      }
+    }
+    if (NS_WARN_IF(!pointToInsert.IsSetAndValid())) {
+      return Err(NS_ERROR_EDITOR_UNEXPECTED_DOM_TREE);
+    }
+    return MoveNodeResult::HandledResult(std::move(pointToInsert));
+  }
+
+  // Check if this node can go into the destination node
+  if (HTMLEditUtils::CanNodeContain(*aPointToInsert.GetContainer(),
+                                    aContentToMove)) {
+    EditorDOMPoint pointToInsert(aPointToInsert);
+    // Preserve white-space in the new position with using `style` attribute.
+    // This is additional path from point of view of our traditional behavior.
+    // Therefore, ignore errors especially if we got unexpected DOM tree.
+    if (destWhiteSpaceStyle.isSome() && srcWhiteSpaceStyle.isSome() &&
+        destWhiteSpaceStyle.value() != srcWhiteSpaceStyle.value()) {
+      // Set `white-space` with `style` attribute if it's nsStyledElement.
+      if (nsStyledElement* styledElement =
+              nsStyledElement::FromNode(&aContentToMove)) {
+        DebugOnly<nsresult> rvIgnored =
+            CSSEditUtils::SetCSSPropertyWithTransaction(
+                *this, MOZ_KnownLive(*styledElement), *nsGkAtoms::white_space,
+                GetWhiteSpaceStyleValue(srcWhiteSpaceStyle.value()));
+        if (NS_WARN_IF(Destroyed())) {
+          return Err(NS_ERROR_EDITOR_DESTROYED);
+        }
+        NS_WARNING_ASSERTION(NS_SUCCEEDED(rvIgnored),
+                             "CSSEditUtils::SetCSSPropertyWithTransaction("
+                             "nsGkAtoms::white_space) failed, but ignored");
+      }
+      // Otherwise, if the dest container can have <span> element and <span>
+      // element can have the moving content node, we should insert it.
+      else if (HTMLEditUtils::CanNodeContain(*aPointToInsert.GetContainer(),
+                                             *nsGkAtoms::span) &&
+               HTMLEditUtils::CanNodeContain(*nsGkAtoms::span,
+                                             aContentToMove)) {
+        RefPtr<Element> newSpanElement = CreateHTMLContent(nsGkAtoms::span);
+        if (NS_WARN_IF(!newSpanElement)) {
+          return Err(NS_ERROR_FAILURE);
+        }
+        nsAutoString styleAttrValue(u"white-space: "_ns);
+        styleAttrValue.Append(
+            GetWhiteSpaceStyleValue(srcWhiteSpaceStyle.value()));
+        IgnoredErrorResult error;
+        newSpanElement->SetAttr(nsGkAtoms::style, styleAttrValue, error);
+        NS_WARNING_ASSERTION(!error.Failed(),
+                             "Element::SetAttr(nsGkAtoms::span) failed");
+        if (MOZ_LIKELY(!error.Failed())) {
+          Result<CreateElementResult, nsresult> insertSpanElementResult =
+              InsertNodeWithTransaction<Element>(*newSpanElement,
+                                                 aPointToInsert);
+          if (MOZ_UNLIKELY(insertSpanElementResult.isErr())) {
+            if (NS_WARN_IF(insertSpanElementResult.inspectErr() ==
+                           NS_ERROR_EDITOR_DESTROYED)) {
+              return Err(NS_ERROR_EDITOR_DESTROYED);
+            }
+            NS_WARNING(
+                "HTMLEditor::InsertNodeWithTransaction() failed, but ignored");
+          } else {
+            // We should move the node into the new <span> to preserve the
+            // style.
+            pointToInsert.Set(newSpanElement, 0u);
+            // We should put caret after aContentToMove after moving it so that
+            // we do not need the suggested caret point here.
+            insertSpanElementResult.inspect().IgnoreCaretPointSuggestion();
+          }
+        }
+      }
+    }
+    // If it can, move it there.
+    Result<MoveNodeResult, nsresult> moveNodeResult =
+        MoveNodeWithTransaction(aContentToMove, pointToInsert);
+    NS_WARNING_ASSERTION(moveNodeResult.isOk(),
+                         "HTMLEditor::MoveNodeWithTransaction() failed");
+    // XXX This is odd to override the handled state here, but stopping this
+    //     hits an NS_ASSERTION in WhiteSpaceVisibilityKeeper::
+    //     MergeFirstLineOfRightBlockElementIntoAncestorLeftBlockElement.
+    if (moveNodeResult.isOk()) {
+      MoveNodeResult unwrappedMoveNodeResult = moveNodeResult.unwrap();
+      unwrappedMoveNodeResult.MarkAsHandled();
+      return unwrappedMoveNodeResult;
+    }
+    return moveNodeResult;
+  }
+
+  // If it can't, move its children (if any), and then delete it.
+  auto moveNodeResult =
+      [&]() MOZ_CAN_RUN_SCRIPT -> Result<MoveNodeResult, nsresult> {
+    if (!aContentToMove.IsElement()) {
+      return MoveNodeResult::HandledResult(aPointToInsert);
+    }
+    Result<MoveNodeResult, nsresult> moveChildrenResult =
+        MoveChildrenWithTransaction(MOZ_KnownLive(*aContentToMove.AsElement()),
+                                    aPointToInsert, aPreserveWhiteSpaceStyle,
+                                    aRemoveIfCommentNode);
+    NS_WARNING_ASSERTION(moveChildrenResult.isOk(),
+                         "HTMLEditor::MoveChildrenWithTransaction() failed");
+    return moveChildrenResult;
+  }();
+  if (MOZ_UNLIKELY(moveNodeResult.isErr())) {
+    return moveNodeResult;  // Already warned in the lambda.
+  }
+
+  nsresult rv = DeleteNodeWithTransaction(aContentToMove);
+  if (NS_FAILED(rv)) {
+    NS_WARNING("EditorBase::DeleteNodeWithTransaction() failed");
+    moveNodeResult.inspect().IgnoreCaretPointSuggestion();
+    return Err(rv);
+  }
+  if (!MayHaveMutationEventListeners()) {
+    return moveNodeResult;
+  }
+  // Mutation event listener may make `offset` value invalid with
+  // removing some previous children while we call
+  // `DeleteNodeWithTransaction()` so that we should adjust it here.
+  if (moveNodeResult.inspect().NextInsertionPointRef().IsSetAndValid()) {
+    return moveNodeResult;
+  }
+  moveNodeResult.inspect().IgnoreCaretPointSuggestion();
+  return MoveNodeResult::HandledResult(
+      EditorDOMPoint::AtEndOf(*aPointToInsert.GetContainer()));
+}
+
+Result<bool, nsresult> HTMLEditor::CanMoveChildren(
+    const Element& aElement, const nsINode& aNewContainer) const {
+  if (NS_WARN_IF(&aElement == &aNewContainer)) {
+    return Err(NS_ERROR_FAILURE);
+  }
+  for (nsIContent* childContent = aElement.GetFirstChild(); childContent;
+       childContent = childContent->GetNextSibling()) {
+    Result<bool, nsresult> result =
+        CanMoveNodeOrChildren(*childContent, aNewContainer);
+    if (result.isErr() || result.inspect()) {
+      return result;
+    }
+  }
+  return false;
+}
+
+Result<MoveNodeResult, nsresult> HTMLEditor::MoveChildrenWithTransaction(
+    Element& aElement, const EditorDOMPoint& aPointToInsert,
+    PreserveWhiteSpaceStyle aPreserveWhiteSpaceStyle,
+    RemoveIfCommentNode aRemoveIfCommentNode) {
+  MOZ_ASSERT(aPointToInsert.IsSet());
+
+  if (NS_WARN_IF(&aElement == aPointToInsert.GetContainer())) {
+    return Err(NS_ERROR_INVALID_ARG);
+  }
+
+  MoveNodeResult moveChildrenResult =
+      MoveNodeResult::IgnoredResult(aPointToInsert);
+  while (aElement.GetFirstChild()) {
+    Result<MoveNodeResult, nsresult> moveNodeOrChildrenResult =
+        MoveNodeOrChildrenWithTransaction(
+            MOZ_KnownLive(*aElement.GetFirstChild()),
+            moveChildrenResult.NextInsertionPointRef(),
+            aPreserveWhiteSpaceStyle, aRemoveIfCommentNode);
+    if (MOZ_UNLIKELY(moveNodeOrChildrenResult.isErr())) {
+      NS_WARNING("HTMLEditor::MoveNodeOrChildrenWithTransaction() failed");
+      moveChildrenResult.IgnoreCaretPointSuggestion();
+      return moveNodeOrChildrenResult;
+    }
+    moveChildrenResult |= moveNodeOrChildrenResult.inspect();
+  }
+  return moveChildrenResult;
+}
+
+void HTMLEditor::MoveAllChildren(nsINode& aContainer,
+                                 const EditorRawDOMPoint& aPointToInsert,
+                                 ErrorResult& aError) {
+  MOZ_ASSERT(!aError.Failed());
+
+  if (!aContainer.HasChildren()) {
+    return;
+  }
+  nsIContent* firstChild = aContainer.GetFirstChild();
+  if (NS_WARN_IF(!firstChild)) {
+    aError.Throw(NS_ERROR_FAILURE);
+    return;
+  }
+  nsIContent* lastChild = aContainer.GetLastChild();
+  if (NS_WARN_IF(!lastChild)) {
+    aError.Throw(NS_ERROR_FAILURE);
+    return;
+  }
+  MoveChildrenBetween(*firstChild, *lastChild, aPointToInsert, aError);
+  NS_WARNING_ASSERTION(!aError.Failed(),
+                       "HTMLEditor::MoveChildrenBetween() failed");
+}
+
+void HTMLEditor::MoveChildrenBetween(nsIContent& aFirstChild,
+                                     nsIContent& aLastChild,
+                                     const EditorRawDOMPoint& aPointToInsert,
+                                     ErrorResult& aError) {
+  nsCOMPtr<nsINode> oldContainer = aFirstChild.GetParentNode();
+  if (NS_WARN_IF(oldContainer != aLastChild.GetParentNode()) ||
+      NS_WARN_IF(!aPointToInsert.IsInContentNode()) ||
+      NS_WARN_IF(!aPointToInsert.CanContainerHaveChildren())) {
+    aError.Throw(NS_ERROR_INVALID_ARG);
+    return;
+  }
+
+  // First, store all children which should be moved to the new container.
+  AutoTArray<nsCOMPtr<nsIContent>, 10> children;
+  for (nsIContent* child = &aFirstChild; child;
+       child = child->GetNextSibling()) {
+    children.AppendElement(child);
+    if (child == &aLastChild) {
+      break;
+    }
+  }
+
+  if (NS_WARN_IF(children.LastElement() != &aLastChild)) {
+    aError.Throw(NS_ERROR_INVALID_ARG);
+    return;
+  }
+
+  nsCOMPtr<nsIContent> newContainer = aPointToInsert.ContainerAs<nsIContent>();
+  nsCOMPtr<nsIContent> nextNode = aPointToInsert.GetChild();
+  for (size_t i = children.Length(); i > 0; --i) {
+    nsCOMPtr<nsIContent>& child = children[i - 1];
+    if (child->GetParentNode() != oldContainer) {
+      // If the child has been moved to different container, we shouldn't
+      // touch it.
+      continue;
+    }
+    if (NS_WARN_IF(!HTMLEditUtils::IsRemovableNode(*child))) {
+      aError.Throw(NS_ERROR_EDITOR_UNEXPECTED_DOM_TREE);
+      return;
+    }
+    oldContainer->RemoveChild(*child, aError);
+    if (NS_WARN_IF(Destroyed())) {
+      aError.Throw(NS_ERROR_EDITOR_DESTROYED);
+      return;
+    }
+    if (aError.Failed()) {
+      NS_WARNING("nsINode::RemoveChild() failed");
+      return;
+    }
+    if (nextNode) {
+      // If we're not appending the children to the new container, we should
+      // check if referring next node of insertion point is still in the new
+      // container.
+      EditorRawDOMPoint pointToInsert(nextNode);
+      if (NS_WARN_IF(!pointToInsert.IsSet()) ||
+          NS_WARN_IF(pointToInsert.GetContainer() != newContainer)) {
+        // The next node of insertion point has been moved by mutation observer.
+        // Let's stop moving the remaining nodes.
+        // XXX Or should we move remaining children after the last moved child?
+        aError.Throw(NS_ERROR_FAILURE);
+        return;
+      }
+    }
+    if (NS_WARN_IF(
+            !EditorUtils::IsEditableContent(*newContainer, EditorType::HTML))) {
+      aError.Throw(NS_ERROR_EDITOR_UNEXPECTED_DOM_TREE);
+      return;
+    }
+    newContainer->InsertBefore(*child, nextNode, aError);
+    if (NS_WARN_IF(Destroyed())) {
+      aError.Throw(NS_ERROR_EDITOR_DESTROYED);
+      return;
+    }
+    if (aError.Failed()) {
+      NS_WARNING("nsINode::InsertBefore() failed");
+      return;
+    }
+    // If the child was inserted or appended properly, the following children
+    // should be inserted before it.  Otherwise, keep using current position.
+    if (child->GetParentNode() == newContainer) {
+      nextNode = child;
+    }
+  }
+}
+
+void HTMLEditor::MovePreviousSiblings(nsIContent& aChild,
+                                      const EditorRawDOMPoint& aPointToInsert,
+                                      ErrorResult& aError) {
+  MOZ_ASSERT(!aError.Failed());
+
+  if (NS_WARN_IF(!aChild.GetParentNode())) {
+    aError.Throw(NS_ERROR_INVALID_ARG);
+    return;
+  }
+  nsIContent* firstChild = aChild.GetParentNode()->GetFirstChild();
+  if (NS_WARN_IF(!firstChild)) {
+    aError.Throw(NS_ERROR_FAILURE);
+    return;
+  }
+  nsIContent* lastChild =
+      &aChild == firstChild ? firstChild : aChild.GetPreviousSibling();
+  if (NS_WARN_IF(!lastChild)) {
+    aError.Throw(NS_ERROR_FAILURE);
+    return;
+  }
+  MoveChildrenBetween(*firstChild, *lastChild, aPointToInsert, aError);
+  NS_WARNING_ASSERTION(!aError.Failed(),
+                       "HTMLEditor::MoveChildrenBetween() failed");
+}
+
+void HTMLEditor::MoveInclusiveNextSiblings(
+    nsIContent& aChild, const EditorRawDOMPoint& aPointToInsert,
+    ErrorResult& aError) {
+  MOZ_ASSERT(!aError.Failed());
+
+  if (NS_WARN_IF(!aChild.GetParentNode())) {
+    aError.Throw(NS_ERROR_INVALID_ARG);
+    return;
+  }
+  nsIContent* lastChild = aChild.GetParentNode()->GetLastChild();
+  if (NS_WARN_IF(!lastChild)) {
+    aError.Throw(NS_ERROR_FAILURE);
+    return;
+  }
+  MoveChildrenBetween(aChild, *lastChild, aPointToInsert, aError);
+  NS_WARNING_ASSERTION(!aError.Failed(),
+                       "HTMLEditor::MoveChildrenBetween() failed");
+}
+
+nsresult HTMLEditor::AutoDeleteRangesHandler::AutoBlockElementsJoiner::
+    DeleteContentButKeepTableStructure(HTMLEditor& aHTMLEditor,
+                                       nsIContent& aContent) {
+  MOZ_ASSERT(aHTMLEditor.IsEditActionDataAvailable());
+
+  if (!HTMLEditUtils::IsAnyTableElementButNotTable(&aContent)) {
+    nsresult rv = aHTMLEditor.DeleteNodeWithTransaction(aContent);
+    NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                         "EditorBase::DeleteNodeWithTransaction() failed");
+    return rv;
+  }
+
+  // XXX For performance, this should just call
+  //     DeleteContentButKeepTableStructure() while there are children in
+  //     aContent.  If we need to avoid infinite loop because mutation event
+  //     listeners can add unexpected nodes into aContent, we should just loop
+  //     only original count of the children.
+  AutoTArray<OwningNonNull<nsIContent>, 10> childList;
+  for (nsIContent* child = aContent.GetFirstChild(); child;
+       child = child->GetNextSibling()) {
+    childList.AppendElement(*child);
+  }
+
+  for (const auto& child : childList) {
+    // MOZ_KnownLive because 'childList' is guaranteed to
+    // keep it alive.
+    nsresult rv =
+        DeleteContentButKeepTableStructure(aHTMLEditor, MOZ_KnownLive(child));
+    if (NS_FAILED(rv)) {
+      NS_WARNING("HTMLEditor::DeleteContentButKeepTableStructure() failed");
+      return rv;
+    }
+  }
+  return NS_OK;
+}
+
+nsresult HTMLEditor::DeleteMostAncestorMailCiteElementIfEmpty(
+    nsIContent& aContent) {
+  MOZ_ASSERT(IsEditActionDataAvailable());
+
+  // The element must be `<blockquote type="cite">` or
+  // `<span _moz_quote="true">`.
+  RefPtr<Element> mailCiteElement =
+      GetMostDistantAncestorMailCiteElement(aContent);
+  if (!mailCiteElement) {
+    return NS_OK;
+  }
+  bool seenBR = false;
+  if (!HTMLEditUtils::IsEmptyNode(*mailCiteElement,
+                                  {EmptyCheckOption::TreatListItemAsVisible,
+                                   EmptyCheckOption::TreatTableCellAsVisible},
+                                  &seenBR)) {
+    return NS_OK;
+  }
+  EditorDOMPoint atEmptyMailCiteElement(mailCiteElement);
+  {
+    AutoEditorDOMPointChildInvalidator lockOffset(atEmptyMailCiteElement);
+    nsresult rv = DeleteNodeWithTransaction(*mailCiteElement);
+    if (NS_FAILED(rv)) {
+      NS_WARNING("EditorBase::DeleteNodeWithTransaction() failed");
+      return rv;
+    }
+  }
+
+  if (!atEmptyMailCiteElement.IsSet() || !seenBR) {
+    NS_WARNING_ASSERTION(
+        atEmptyMailCiteElement.IsSet(),
+        "Mutation event listener might changed the DOM tree during "
+        "EditorBase::DeleteNodeWithTransaction(), but ignored");
+    return NS_OK;
+  }
+
+  Result<CreateElementResult, nsresult> insertBRElementResult =
+      InsertBRElement(WithTransaction::Yes, atEmptyMailCiteElement);
+  if (MOZ_UNLIKELY(insertBRElementResult.isErr())) {
+    NS_WARNING("HTMLEditor::InsertBRElement(WithTransaction::Yes) failed");
+    return insertBRElementResult.unwrapErr();
+  }
+  MOZ_ASSERT(insertBRElementResult.inspect().GetNewNode());
+  insertBRElementResult.inspect().IgnoreCaretPointSuggestion();
+  nsresult rv = CollapseSelectionTo(
+      EditorRawDOMPoint(insertBRElementResult.inspect().GetNewNode()));
+  if (NS_WARN_IF(rv == NS_ERROR_EDITOR_DESTROYED)) {
+    return NS_ERROR_EDITOR_DESTROYED;
+  }
+  NS_WARNING_ASSERTION(
+      NS_SUCCEEDED(rv),
+      "EditorBase::::CollapseSelectionTo() failed, but ignored");
+  return NS_OK;
+}
+
+Element* HTMLEditor::AutoDeleteRangesHandler::AutoEmptyBlockAncestorDeleter::
+    ScanEmptyBlockInclusiveAncestor(const HTMLEditor& aHTMLEditor,
+                                    nsIContent& aStartContent) {
+  MOZ_ASSERT(aHTMLEditor.IsEditActionDataAvailable());
+  MOZ_ASSERT(!mEmptyInclusiveAncestorBlockElement);
+
+  // If we are inside an empty block, delete it.
+  // Note: do NOT delete table elements this way.
+  // Note: do NOT delete non-editable block element.
+  Element* editableBlockElement = HTMLEditUtils::GetInclusiveAncestorElement(
+      aStartContent, HTMLEditUtils::ClosestEditableBlockElement);
+  if (!editableBlockElement) {
+    return nullptr;
+  }
+  // XXX Perhaps, this is slow loop.  If empty blocks are nested, then,
+  //     each block checks whether it's empty or not.  However, descendant
+  //     blocks are checked again and again by IsEmptyNode().  Perhaps, it
+  //     should be able to take "known empty element" for avoiding same checks.
+  while (editableBlockElement &&
+         HTMLEditUtils::IsRemovableFromParentNode(*editableBlockElement) &&
+         !HTMLEditUtils::IsAnyTableElement(editableBlockElement) &&
+         HTMLEditUtils::IsEmptyNode(*editableBlockElement)) {
+    // If the removable empty list item is a child of editing host list element,
+    // we should not delete it.
+    if (HTMLEditUtils::IsListItem(editableBlockElement)) {
+      Element* const parentElement = editableBlockElement->GetParentElement();
+      if (parentElement && HTMLEditUtils::IsAnyListElement(parentElement) &&
+          !HTMLEditUtils::IsRemovableFromParentNode(*parentElement) &&
+          HTMLEditUtils::IsEmptyNode(*parentElement)) {
+        break;
+      }
+    }
+    mEmptyInclusiveAncestorBlockElement = editableBlockElement;
+    editableBlockElement = HTMLEditUtils::GetAncestorElement(
+        *mEmptyInclusiveAncestorBlockElement,
+        HTMLEditUtils::ClosestEditableBlockElement);
+  }
+  if (!mEmptyInclusiveAncestorBlockElement) {
+    return nullptr;
+  }
+
+  // XXX Because of not checking whether found block element is editable
+  //     in the above loop, empty ediable block element may be overwritten
+  //     with empty non-editable clock element.  Therefore, we fail to
+  //     remove the found empty nodes.
+  if (NS_WARN_IF(!mEmptyInclusiveAncestorBlockElement->IsEditable()) ||
+      NS_WARN_IF(!mEmptyInclusiveAncestorBlockElement->GetParentElement())) {
+    mEmptyInclusiveAncestorBlockElement = nullptr;
+  }
+  return mEmptyInclusiveAncestorBlockElement;
+}
+
+nsresult HTMLEditor::AutoDeleteRangesHandler::AutoEmptyBlockAncestorDeleter::
+    ComputeTargetRanges(const HTMLEditor& aHTMLEditor,
+                        nsIEditor::EDirection aDirectionAndAmount,
+                        const Element& aEditingHost,
+                        AutoRangeArray& aRangesToDelete) const {
+  MOZ_ASSERT(mEmptyInclusiveAncestorBlockElement);
+
+  // We'll delete `mEmptyInclusiveAncestorBlockElement` node from the tree, but
+  // we should return the range from start/end of next/previous editable content
+  // to end/start of the element for compatiblity with the other browsers.
+  switch (aDirectionAndAmount) {
+    case nsIEditor::eNone:
+      break;
+    case nsIEditor::ePrevious:
+    case nsIEditor::ePreviousWord:
+    case nsIEditor::eToBeginningOfLine: {
+      EditorRawDOMPoint startPoint =
+          HTMLEditUtils::GetPreviousEditablePoint<EditorRawDOMPoint>(
+              *mEmptyInclusiveAncestorBlockElement, &aEditingHost,
+              // In this case, we don't join block elements so that we won't
+              // delete invisible trailing whitespaces in the previous element.
+              InvisibleWhiteSpaces::Preserve,
+              // In this case, we won't join table cells so that we should
+              // get a range which is in a table cell even if it's in a
+              // table.
+              TableBoundary::NoCrossAnyTableElement);
+      if (!startPoint.IsSet()) {
+        NS_WARNING(
+            "HTMLEditUtils::GetPreviousEditablePoint() didn't return a valid "
+            "point");
+        return NS_ERROR_FAILURE;
+      }
+      nsresult rv = aRangesToDelete.SetStartAndEnd(
+          startPoint,
+          EditorRawDOMPoint::AtEndOf(mEmptyInclusiveAncestorBlockElement));
+      NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                           "AutoRangeArray::SetStartAndEnd() failed");
+      return rv;
+    }
+    case nsIEditor::eNext:
+    case nsIEditor::eNextWord:
+    case nsIEditor::eToEndOfLine: {
+      EditorRawDOMPoint endPoint =
+          HTMLEditUtils::GetNextEditablePoint<EditorRawDOMPoint>(
+              *mEmptyInclusiveAncestorBlockElement, &aEditingHost,
+              // In this case, we don't join block elements so that we won't
+              // delete invisible trailing whitespaces in the next element.
+              InvisibleWhiteSpaces::Preserve,
+              // In this case, we won't join table cells so that we should
+              // get a range which is in a table cell even if it's in a
+              // table.
+              TableBoundary::NoCrossAnyTableElement);
+      if (!endPoint.IsSet()) {
+        NS_WARNING(
+            "HTMLEditUtils::GetNextEditablePoint() didn't return a valid "
+            "point");
+        return NS_ERROR_FAILURE;
+      }
+      nsresult rv = aRangesToDelete.SetStartAndEnd(
+          EditorRawDOMPoint(mEmptyInclusiveAncestorBlockElement, 0), endPoint);
+      NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                           "AutoRangeArray::SetStartAndEnd() failed");
+      return rv;
+    }
+    default:
+      MOZ_ASSERT_UNREACHABLE("Handle the nsIEditor::EDirection value");
+      break;
+  }
+  // No direction, let's select the element to be deleted.
+  nsresult rv =
+      aRangesToDelete.SelectNode(*mEmptyInclusiveAncestorBlockElement);
+  NS_WARNING_ASSERTION(NS_SUCCEEDED(rv), "AutoRangeArray::SelectNode() failed");
+  return rv;
+}
+
+Result<RefPtr<Element>, nsresult>
+HTMLEditor::AutoDeleteRangesHandler::AutoEmptyBlockAncestorDeleter::
+    MaybeInsertBRElementBeforeEmptyListItemElement(HTMLEditor& aHTMLEditor) {
+  MOZ_ASSERT(mEmptyInclusiveAncestorBlockElement);
+  MOZ_ASSERT(mEmptyInclusiveAncestorBlockElement->GetParentElement());
+  MOZ_ASSERT(HTMLEditUtils::IsListItem(mEmptyInclusiveAncestorBlockElement));
+
+  // If the found empty block is a list item element and its grand parent
+  // (i.e., parent of list element) is NOT a list element, insert <br>
+  // element before the list element which has the empty list item.
+  // This odd list structure may occur if `Document.execCommand("indent")`
+  // is performed for list items.
+  // XXX Chrome does not remove empty list elements when last content in
+  //     last list item is deleted.  We should follow it since current
+  //     behavior is annoying when you type new list item with selecting
+  //     all list items.
+  if (!HTMLEditUtils::IsFirstChild(*mEmptyInclusiveAncestorBlockElement,
+                                   {WalkTreeOption::IgnoreNonEditableNode})) {
+    return RefPtr<Element>();
+  }
+
+  EditorDOMPoint atParentOfEmptyListItem(
+      mEmptyInclusiveAncestorBlockElement->GetParentElement());
+  if (NS_WARN_IF(!atParentOfEmptyListItem.IsSet())) {
+    return Err(NS_ERROR_FAILURE);
+  }
+  if (HTMLEditUtils::IsAnyListElement(atParentOfEmptyListItem.GetContainer())) {
+    return RefPtr<Element>();
+  }
+  Result<CreateElementResult, nsresult> insertBRElementResult =
+      aHTMLEditor.InsertBRElement(WithTransaction::Yes,
+                                  atParentOfEmptyListItem);
+  if (MOZ_UNLIKELY(insertBRElementResult.isErr())) {
+    NS_WARNING("HTMLEditor::InsertBRElement(WithTransaction::Yes) failed");
+    return insertBRElementResult.propagateErr();
+  }
+  CreateElementResult unwrappedInsertBRElementResult =
+      insertBRElementResult.unwrap();
+  nsresult rv = unwrappedInsertBRElementResult.SuggestCaretPointTo(
+      aHTMLEditor, {SuggestCaret::OnlyIfHasSuggestion,
+                    SuggestCaret::OnlyIfTransactionsAllowedToDoIt,
+                    SuggestCaret::AndIgnoreTrivialError});
+  if (NS_FAILED(rv)) {
+    NS_WARNING("CreateElementResult::SuggestCaretPointTo() failed");
+    return Err(rv);
+  }
+  MOZ_ASSERT(unwrappedInsertBRElementResult.GetNewNode());
+  return unwrappedInsertBRElementResult.UnwrapNewNode();
+}
+
+Result<CaretPoint, nsresult> HTMLEditor::AutoDeleteRangesHandler::
+    AutoEmptyBlockAncestorDeleter::GetNewCaretPosition(
+        const HTMLEditor& aHTMLEditor,
+        nsIEditor::EDirection aDirectionAndAmount) const {
+  MOZ_ASSERT(mEmptyInclusiveAncestorBlockElement);
+  MOZ_ASSERT(mEmptyInclusiveAncestorBlockElement->GetParentElement());
+  MOZ_ASSERT(aHTMLEditor.IsEditActionDataAvailable());
+
+  switch (aDirectionAndAmount) {
+    case nsIEditor::eNext:
+    case nsIEditor::eNextWord:
+    case nsIEditor::eToEndOfLine: {
+      // Collapse Selection to next node of after empty block element
+      // if there is.  Otherwise, to just after the empty block.
+      auto afterEmptyBlock(
+          EditorDOMPoint::After(mEmptyInclusiveAncestorBlockElement));
+      MOZ_ASSERT(afterEmptyBlock.IsSet());
+      if (nsIContent* nextContentOfEmptyBlock = HTMLEditUtils::GetNextContent(
+              afterEmptyBlock, {}, aHTMLEditor.ComputeEditingHost())) {
+        EditorDOMPoint pt = HTMLEditUtils::GetGoodCaretPointFor<EditorDOMPoint>(
+            *nextContentOfEmptyBlock, aDirectionAndAmount);
+        if (!pt.IsSet()) {
+          NS_WARNING("HTMLEditUtils::GetGoodCaretPointFor() failed");
+          return Err(NS_ERROR_FAILURE);
+        }
+        return CaretPoint(std::move(pt));
+      }
+      if (NS_WARN_IF(!afterEmptyBlock.IsSet())) {
+        return Err(NS_ERROR_FAILURE);
+      }
+      return CaretPoint(std::move(afterEmptyBlock));
+    }
+    case nsIEditor::ePrevious:
+    case nsIEditor::ePreviousWord:
+    case nsIEditor::eToBeginningOfLine: {
+      // Collapse Selection to previous editable node of the empty block
+      // if there is.  Otherwise, to after the empty block.
+      EditorRawDOMPoint atEmptyBlock(mEmptyInclusiveAncestorBlockElement);
+      if (nsIContent* previousContentOfEmptyBlock =
+              HTMLEditUtils::GetPreviousContent(
+                  atEmptyBlock, {WalkTreeOption::IgnoreNonEditableNode},
+                  aHTMLEditor.ComputeEditingHost())) {
+        EditorDOMPoint pt = HTMLEditUtils::GetGoodCaretPointFor<EditorDOMPoint>(
+            *previousContentOfEmptyBlock, aDirectionAndAmount);
+        if (!pt.IsSet()) {
+          NS_WARNING("HTMLEditUtils::GetGoodCaretPointFor() failed");
+          return Err(NS_ERROR_FAILURE);
+        }
+        return CaretPoint(std::move(pt));
+      }
+      auto afterEmptyBlock =
+          EditorDOMPoint::After(*mEmptyInclusiveAncestorBlockElement);
+      if (NS_WARN_IF(!afterEmptyBlock.IsSet())) {
+        return Err(NS_ERROR_FAILURE);
+      }
+      return CaretPoint(std::move(afterEmptyBlock));
+    }
+    case nsIEditor::eNone: {
+      // Collapse selection at the removing block when we are replacing
+      // selected content.
+      EditorDOMPoint atEmptyBlock(mEmptyInclusiveAncestorBlockElement);
+      if (NS_WARN_IF(!atEmptyBlock.IsSet())) {
+        return Err(NS_ERROR_FAILURE);
+      }
+      return CaretPoint(std::move(atEmptyBlock));
+    }
+    default:
+      MOZ_CRASH(
+          "AutoEmptyBlockAncestorDeleter doesn't support this action yet");
+      return Err(NS_ERROR_FAILURE);
+  }
+}
+
+Result<EditActionResult, nsresult>
+HTMLEditor::AutoDeleteRangesHandler::AutoEmptyBlockAncestorDeleter::Run(
+    HTMLEditor& aHTMLEditor, nsIEditor::EDirection aDirectionAndAmount) {
+  MOZ_ASSERT(mEmptyInclusiveAncestorBlockElement);
+  MOZ_ASSERT(mEmptyInclusiveAncestorBlockElement->GetParentElement());
+  MOZ_ASSERT(aHTMLEditor.IsEditActionDataAvailable());
+
+  {
+    Result<EditActionResult, nsresult> result =
+        MaybeReplaceSubListWithNewListItem(aHTMLEditor);
+    if (MOZ_UNLIKELY(result.isErr())) {
+      NS_WARNING(
+          "AutoEmptyBlockAncestorDeleter::MaybeReplaceSubListWithNewListItem() "
+          "failed");
+      return result;
+    }
+    if (result.inspect().Handled()) {
+      return result;
+    }
+  }
+
+  if (HTMLEditUtils::IsListItem(mEmptyInclusiveAncestorBlockElement)) {
+    Result<RefPtr<Element>, nsresult> result =
+        MaybeInsertBRElementBeforeEmptyListItemElement(aHTMLEditor);
+    if (MOZ_UNLIKELY(result.isErr())) {
+      NS_WARNING(
+          "AutoEmptyBlockAncestorDeleter::"
+          "MaybeInsertBRElementBeforeEmptyListItemElement() failed");
+      return result.propagateErr();
+    }
+    // If a `<br>` element is inserted, caret should be moved to after it.
+    if (RefPtr<Element> brElement = result.unwrap()) {
+      nsresult rv =
+          aHTMLEditor.CollapseSelectionTo(EditorRawDOMPoint(brElement));
+      if (NS_FAILED(rv)) {
+        NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                             "EditorBase::CollapseSelectionTo() failed");
+        return Err(rv);
+      }
+    }
+  } else {
+    Result<CaretPoint, nsresult> result =
+        GetNewCaretPosition(aHTMLEditor, aDirectionAndAmount);
+    if (MOZ_UNLIKELY(result.isErr())) {
+      NS_WARNING("AutoEmptyBlockAncestorDeleter::GetNewCaretPosition() failed");
+      return result.propagateErr();
+    }
+    MOZ_ASSERT(result.inspect().HasCaretPointSuggestion());
+    nsresult rv = result.inspect().SuggestCaretPointTo(aHTMLEditor, {});
+    if (NS_FAILED(rv)) {
+      NS_WARNING("CaretPoint::SuggestCaretPointTo() failed");
+      return Err(rv);
+    }
+  }
+  nsresult rv = aHTMLEditor.DeleteNodeWithTransaction(
+      MOZ_KnownLive(*mEmptyInclusiveAncestorBlockElement));
+  if (NS_FAILED(rv)) {
+    NS_WARNING("EditorBase::DeleteNodeWithTransaction() failed");
+    return Err(rv);
+  }
+  return EditActionResult::HandledResult();
+}
+
+Result<EditActionResult, nsresult> HTMLEditor::AutoDeleteRangesHandler::
+    AutoEmptyBlockAncestorDeleter::MaybeReplaceSubListWithNewListItem(
+        HTMLEditor& aHTMLEditor) {
+  // If we're deleting sublist element and it's the last list item of its parent
+  // list, we should replace it with a list element.
+  if (!HTMLEditUtils::IsAnyListElement(mEmptyInclusiveAncestorBlockElement)) {
+    return EditActionResult::IgnoredResult();
+  }
+  RefPtr<Element> parentElement =
+      mEmptyInclusiveAncestorBlockElement->GetParentElement();
+  if (!parentElement || !HTMLEditUtils::IsAnyListElement(parentElement) ||
+      !HTMLEditUtils::IsEmptyNode(*parentElement)) {
+    return EditActionResult::IgnoredResult();
+  }
+
+  nsCOMPtr<nsINode> nextSibling =
+      mEmptyInclusiveAncestorBlockElement->GetNextSibling();
+  nsresult rv = aHTMLEditor.DeleteNodeWithTransaction(
+      MOZ_KnownLive(*mEmptyInclusiveAncestorBlockElement));
+  if (NS_FAILED(rv)) {
+    NS_WARNING("EditorBase::DeleteNodeWithTransaction() failed");
+    return Err(rv);
+  }
+  Result<CreateElementResult, nsresult> insertListItemResult =
+      aHTMLEditor.CreateAndInsertElement(
+          WithTransaction::Yes,
+          parentElement->IsHTMLElement(nsGkAtoms::dl) ? *nsGkAtoms::dd
+                                                      : *nsGkAtoms::li,
+          !nextSibling || nextSibling->GetParentNode() != parentElement
+              ? EditorDOMPoint::AtEndOf(*parentElement)
+              : EditorDOMPoint(nextSibling),
+          [](HTMLEditor& aHTMLEditor, Element& aNewElement,
+             const EditorDOMPoint& aPointToInsert) -> nsresult {
+            RefPtr<Element> brElement =
+                aHTMLEditor.CreateHTMLContent(nsGkAtoms::br);
+            if (MOZ_UNLIKELY(!brElement)) {
+              NS_WARNING(
+                  "EditorBase::CreateHTMLContent(nsGkAtoms::br) failed, but "
+                  "ignored");
+              return NS_OK;  // Just gives up to insert <br>
+            }
+            IgnoredErrorResult error;
+            aNewElement.AppendChild(*brElement, error);
+            NS_WARNING_ASSERTION(!error.Failed(),
+                                 "nsINode::AppendChild() failed, but ignored");
+            return NS_OK;
+          });
+  if (MOZ_UNLIKELY(insertListItemResult.isErr())) {
+    NS_WARNING("HTMLEditor::CreateAndInsertElement() failed");
+    return insertListItemResult.propagateErr();
+  }
+  CreateElementResult unwrappedInsertListItemResult =
+      insertListItemResult.unwrap();
+  unwrappedInsertListItemResult.IgnoreCaretPointSuggestion();
+  rv = aHTMLEditor.CollapseSelectionTo(
+      EditorRawDOMPoint(unwrappedInsertListItemResult.GetNewNode(), 0u));
+  if (NS_FAILED(rv)) {
+    NS_WARNING("EditorBase::CollapseSelectionTo() failed");
+    return Err(rv);
+  }
+  return EditActionResult::HandledResult();
+}
+
+template <typename EditorDOMRangeType>
+Result<EditorRawDOMRange, nsresult>
+HTMLEditor::AutoDeleteRangesHandler::ExtendOrShrinkRangeToDelete(
+    const HTMLEditor& aHTMLEditor, const nsFrameSelection* aFrameSelection,
+    const EditorDOMRangeType& aRangeToDelete) const {
+  MOZ_ASSERT(aHTMLEditor.IsEditActionDataAvailable());
+  MOZ_ASSERT(!aRangeToDelete.Collapsed());
+  MOZ_ASSERT(aRangeToDelete.IsPositioned());
+
+  const nsIContent* commonAncestor = nsIContent::FromNodeOrNull(
+      nsContentUtils::GetClosestCommonInclusiveAncestor(
+          aRangeToDelete.StartRef().GetContainer(),
+          aRangeToDelete.EndRef().GetContainer()));
+  if (MOZ_UNLIKELY(NS_WARN_IF(!commonAncestor))) {
+    return Err(NS_ERROR_FAILURE);
+  }
+
+  // Look for the common ancestor's block element.  It's fine that we get
+  // non-editable block element which is ancestor of inline editing host
+  // because the following code checks editing host too.
+  const Element* const maybeNonEditableBlockElement =
+      HTMLEditUtils::GetInclusiveAncestorElement(
+          *commonAncestor, HTMLEditUtils::ClosestBlockElement);
+  if (NS_WARN_IF(!maybeNonEditableBlockElement)) {
+    return Err(NS_ERROR_FAILURE);
+  }
+
+  // Set up for loops and cache our root element
+  RefPtr<Element> editingHost = aHTMLEditor.ComputeEditingHost();
+  if (NS_WARN_IF(!editingHost)) {
+    return Err(NS_ERROR_FAILURE);
+  }
+
+  // If only one list element is selected, and if the list element is empty,
+  // we should delete only the list element.  Or if the list element is not
+  // empty, we should make the list has only one empty list item element.
+  if (const Element* maybeListElement =
+          HTMLEditUtils::GetElementIfOnlyOneSelected(aRangeToDelete)) {
+    if (HTMLEditUtils::IsAnyListElement(maybeListElement) &&
+        !HTMLEditUtils::IsEmptyAnyListElement(*maybeListElement)) {
+      EditorRawDOMRange range =
+          HTMLEditUtils::GetRangeSelectingAllContentInAllListItems<
+              EditorRawDOMRange>(*maybeListElement);
+      if (range.IsPositioned()) {
+        if (EditorUtils::IsEditableContent(
+                *range.StartRef().ContainerAs<nsIContent>(),
+                EditorType::HTML) &&
+            EditorUtils::IsEditableContent(
+                *range.EndRef().ContainerAs<nsIContent>(), EditorType::HTML)) {
+          return range;
+        }
+      }
+      // If the first and/or last list item is not editable, we need to do more
+      // complicated things probably, but we just delete the list element with
+      // invisible things around it for now since it must be rare case.
+    }
+    // Otherwise, if the list item is empty, we should delete it with invisible
+    // things around it.
+  }
+
+  // Find previous visible things before start of selection
+  EditorRawDOMRange rangeToDelete(aRangeToDelete);
+  if (rangeToDelete.StartRef().GetContainer() != maybeNonEditableBlockElement &&
+      rangeToDelete.StartRef().GetContainer() != editingHost) {
+    for (;;) {
+      WSScanResult backwardScanFromStartResult =
+          WSRunScanner::ScanPreviousVisibleNodeOrBlockBoundary(
+              editingHost, rangeToDelete.StartRef());
+      if (!backwardScanFromStartResult.ReachedCurrentBlockBoundary()) {
+        break;
+      }
+      MOZ_ASSERT(backwardScanFromStartResult.GetContent() ==
+                 WSRunScanner(editingHost, rangeToDelete.StartRef())
+                     .GetStartReasonContent());
+      // We want to keep looking up.  But stop if we are crossing table
+      // element boundaries, or if we hit the root.
+      if (HTMLEditUtils::IsAnyTableElement(
+              backwardScanFromStartResult.GetContent()) ||
+          backwardScanFromStartResult.GetContent() ==
+              maybeNonEditableBlockElement ||
+          backwardScanFromStartResult.GetContent() == editingHost) {
+        break;
+      }
+      // Don't cross list element boundary because we don't want to delete list
+      // element at start position unless it's empty.
+      if (HTMLEditUtils::IsAnyListElement(
+              backwardScanFromStartResult.GetContent()) &&
+          !HTMLEditUtils::IsEmptyAnyListElement(
+              *backwardScanFromStartResult.ElementPtr())) {
+        break;
+      }
+      rangeToDelete.SetStart(
+          backwardScanFromStartResult.PointAtContent<EditorRawDOMPoint>());
+    }
+    if (aFrameSelection && !aFrameSelection->IsValidSelectionPoint(
+                               rangeToDelete.StartRef().GetContainer())) {
+      NS_WARNING("Computed start container was out of selection limiter");
+      return Err(NS_ERROR_FAILURE);
+    }
+  }
+
+  // Expand selection endpoint only if we don't pass an invisible `<br>`, or if
+  // we really needed to pass that `<br>` (i.e., its block is now totally
+  // selected).
+
+  // Find next visible things after end of selection
+  EditorDOMPoint atFirstInvisibleBRElement;
+  if (rangeToDelete.EndRef().GetContainer() != maybeNonEditableBlockElement &&
+      rangeToDelete.EndRef().GetContainer() != editingHost) {
+    for (;;) {
+      WSRunScanner wsScannerAtEnd(editingHost, rangeToDelete.EndRef());
+      WSScanResult forwardScanFromEndResult =
+          wsScannerAtEnd.ScanNextVisibleNodeOrBlockBoundaryFrom(
+              rangeToDelete.EndRef());
+      if (forwardScanFromEndResult.ReachedBRElement()) {
+        // XXX In my understanding, this is odd.  The end reason may not be
+        //     same as the reached <br> element because the equality is
+        //     guaranteed only when ReachedCurrentBlockBoundary() returns true.
+        //     However, looks like that this code assumes that
+        //     GetEndReasonContent() returns the (or a) <br> element.
+        NS_ASSERTION(wsScannerAtEnd.GetEndReasonContent() ==
+                         forwardScanFromEndResult.BRElementPtr(),
+                     "End reason is not the reached <br> element");
+        if (HTMLEditUtils::IsVisibleBRElement(
+                *wsScannerAtEnd.GetEndReasonContent())) {
+          break;
+        }
+        if (!atFirstInvisibleBRElement.IsSet()) {
+          atFirstInvisibleBRElement =
+              rangeToDelete.EndRef().To<EditorDOMPoint>();
+        }
+        rangeToDelete.SetEnd(
+            EditorRawDOMPoint::After(*wsScannerAtEnd.GetEndReasonContent()));
+        continue;
+      }
+
+      if (forwardScanFromEndResult.ReachedCurrentBlockBoundary()) {
+        MOZ_ASSERT(forwardScanFromEndResult.GetContent() ==
+                   wsScannerAtEnd.GetEndReasonContent());
+        // We want to keep looking up.  But stop if we are crossing table
+        // element boundaries, or if we hit the root.
+        if (HTMLEditUtils::IsAnyTableElement(
+                forwardScanFromEndResult.GetContent()) ||
+            forwardScanFromEndResult.GetContent() ==
+                maybeNonEditableBlockElement ||
+            forwardScanFromEndResult.GetContent() == editingHost) {
+          break;
+        }
+        rangeToDelete.SetEnd(
+            forwardScanFromEndResult.PointAfterContent<EditorRawDOMPoint>());
+        continue;
+      }
+
+      break;
+    }
+
+    if (aFrameSelection && !aFrameSelection->IsValidSelectionPoint(
+                               rangeToDelete.EndRef().GetContainer())) {
+      NS_WARNING("Computed end container was out of selection limiter");
+      return Err(NS_ERROR_FAILURE);
+    }
+  }
+
+  // If range boundaries are in list element, and the positions are very
+  // start/end of first/last list item, we may need to shrink the ranges for
+  // preventing to remove only all list item elements.
+  {
+    EditorRawDOMRange rangeToDeleteListOrLeaveOneEmptyListItem =
+        AutoDeleteRangesHandler::
+            GetRangeToAvoidDeletingAllListItemsIfSelectingAllOverListElements(
+                rangeToDelete);
+    if (rangeToDeleteListOrLeaveOneEmptyListItem.IsPositioned()) {
+      rangeToDelete = std::move(rangeToDeleteListOrLeaveOneEmptyListItem);
+    }
+  }
+
+  if (atFirstInvisibleBRElement.IsInContentNode()) {
+    // Find block node containing invisible `<br>` element.
+    if (const RefPtr<const Element> editableBlockContainingBRElement =
+            HTMLEditUtils::GetInclusiveAncestorElement(
+                *atFirstInvisibleBRElement.ContainerAs<nsIContent>(),
+                HTMLEditUtils::ClosestEditableBlockElement)) {
+      if (rangeToDelete.Contains(
+              EditorRawDOMPoint(editableBlockContainingBRElement))) {
+        return rangeToDelete;
+      }
+      // Otherwise, the new range should end at the invisible `<br>`.
+      if (aFrameSelection && !aFrameSelection->IsValidSelectionPoint(
+                                 atFirstInvisibleBRElement.GetContainer())) {
+        NS_WARNING(
+            "Computed end container (`<br>` element) was out of selection "
+            "limiter");
+        return Err(NS_ERROR_FAILURE);
+      }
+      rangeToDelete.SetEnd(atFirstInvisibleBRElement);
+    }
+  }
+
+  return rangeToDelete;
+}
+
+// static
+EditorRawDOMRange HTMLEditor::AutoDeleteRangesHandler::
+    GetRangeToAvoidDeletingAllListItemsIfSelectingAllOverListElements(
+        const EditorRawDOMRange& aRangeToDelete) {
+  MOZ_ASSERT(aRangeToDelete.IsPositionedAndValid());
+
+  auto GetDeepestEditableStartPointOfList = [](Element& aListElement) {
+    Element* const firstListItemElement =
+        HTMLEditUtils::GetFirstListItemElement(aListElement);
+    if (MOZ_UNLIKELY(!firstListItemElement)) {
+      return EditorRawDOMPoint();
+    }
+    if (MOZ_UNLIKELY(!EditorUtils::IsEditableContent(*firstListItemElement,
+                                                     EditorType::HTML))) {
+      return EditorRawDOMPoint(firstListItemElement);
+    }
+    return HTMLEditUtils::GetDeepestEditableStartPointOf<EditorRawDOMPoint>(
+        *firstListItemElement);
+  };
+
+  auto GetDeepestEditableEndPointOfList = [](Element& aListElement) {
+    Element* const lastListItemElement =
+        HTMLEditUtils::GetLastListItemElement(aListElement);
+    if (MOZ_UNLIKELY(!lastListItemElement)) {
+      return EditorRawDOMPoint();
+    }
+    if (MOZ_UNLIKELY(!EditorUtils::IsEditableContent(*lastListItemElement,
+                                                     EditorType::HTML))) {
+      return EditorRawDOMPoint::After(*lastListItemElement);
+    }
+    return HTMLEditUtils::GetDeepestEditableEndPointOf<EditorRawDOMPoint>(
+        *lastListItemElement);
+  };
+
+  Element* const startListElement =
+      aRangeToDelete.StartRef().IsInContentNode()
+          ? HTMLEditUtils::GetClosestInclusiveAncestorAnyListElement(
+                *aRangeToDelete.StartRef().ContainerAs<nsIContent>())
+          : nullptr;
+  Element* const endListElement =
+      aRangeToDelete.EndRef().IsInContentNode()
+          ? HTMLEditUtils::GetClosestInclusiveAncestorAnyListElement(
+                *aRangeToDelete.EndRef().ContainerAs<nsIContent>())
+          : nullptr;
+  if (!startListElement && !endListElement) {
+    return EditorRawDOMRange();
+  }
+
+  // FIXME: If there are invalid children, we cannot handle first/last list item
+  // elements properly.  In that case, we should treat list elements and list
+  // item elements as normal block elements.
+  if (startListElement &&
+      NS_WARN_IF(!HTMLEditUtils::IsValidListElement(
+          *startListElement, HTMLEditUtils::TreatSubListElementAs::Valid))) {
+    return EditorRawDOMRange();
+  }
+  if (endListElement && startListElement != endListElement &&
+      NS_WARN_IF(!HTMLEditUtils::IsValidListElement(
+          *endListElement, HTMLEditUtils::TreatSubListElementAs::Valid))) {
+    return EditorRawDOMRange();
+  }
+
+  const bool startListElementIsEmpty =
+      startListElement &&
+      HTMLEditUtils::IsEmptyAnyListElement(*startListElement);
+  const bool endListElementIsEmpty =
+      startListElement == endListElement
+          ? startListElementIsEmpty
+          : endListElement &&
+                HTMLEditUtils::IsEmptyAnyListElement(*endListElement);
+  // If both list elements are empty, we should not shrink the range since
+  // we want to delete the list.
+  if (startListElementIsEmpty && endListElementIsEmpty) {
+    return EditorRawDOMRange();
+  }
+
+  // There may be invisible white-spaces and there are elements in the
+  // list items.  Therefore, we need to compare the deepest positions
+  // and range boundaries.
+  EditorRawDOMPoint deepestStartPointOfStartList =
+      startListElement ? GetDeepestEditableStartPointOfList(*startListElement)
+                       : EditorRawDOMPoint();
+  EditorRawDOMPoint deepestEndPointOfEndList =
+      endListElement ? GetDeepestEditableEndPointOfList(*endListElement)
+                     : EditorRawDOMPoint();
+  if (MOZ_UNLIKELY(!deepestStartPointOfStartList.IsSet() &&
+                   !deepestEndPointOfEndList.IsSet())) {
+    // FIXME: This does not work well if there is non-list-item contents in the
+    // list elements.  Perhaps, for fixing this invalid cases, we need to wrap
+    // the content into new list item like Chrome.
+    return EditorRawDOMRange();
+  }
+
+  // We don't want to shrink the range into empty sublist.
+  if (deepestStartPointOfStartList.IsSet()) {
+    for (nsIContent* const maybeList :
+         deepestStartPointOfStartList.GetContainer()
+             ->InclusiveAncestorsOfType<nsIContent>()) {
+      if (aRangeToDelete.StartRef().GetContainer() == maybeList) {
+        break;
+      }
+      if (HTMLEditUtils::IsAnyListElement(maybeList) &&
+          HTMLEditUtils::IsEmptyAnyListElement(*maybeList->AsElement())) {
+        deepestStartPointOfStartList.Set(maybeList);
+      }
+    }
+  }
+  if (deepestEndPointOfEndList.IsSet()) {
+    for (nsIContent* const maybeList :
+         deepestEndPointOfEndList.GetContainer()
+             ->InclusiveAncestorsOfType<nsIContent>()) {
+      if (aRangeToDelete.EndRef().GetContainer() == maybeList) {
+        break;
+      }
+      if (HTMLEditUtils::IsAnyListElement(maybeList) &&
+          HTMLEditUtils::IsEmptyAnyListElement(*maybeList->AsElement())) {
+        deepestEndPointOfEndList.SetAfter(maybeList);
+      }
+    }
+  }
+
+  const EditorRawDOMPoint deepestEndPointOfStartList =
+      startListElement ? GetDeepestEditableEndPointOfList(*startListElement)
+                       : EditorRawDOMPoint();
+  MOZ_ASSERT_IF(deepestStartPointOfStartList.IsSet(),
+                deepestEndPointOfStartList.IsSet());
+  MOZ_ASSERT_IF(!deepestStartPointOfStartList.IsSet(),
+                !deepestEndPointOfStartList.IsSet());
+
+  const bool rangeStartsFromBeginningOfStartList =
+      deepestStartPointOfStartList.IsSet() &&
+      aRangeToDelete.StartRef().EqualsOrIsBefore(deepestStartPointOfStartList);
+  const bool rangeEndsByEndingOfStartListOrLater =
+      !deepestEndPointOfStartList.IsSet() ||
+      deepestEndPointOfStartList.EqualsOrIsBefore(aRangeToDelete.EndRef());
+  const bool rangeEndsByEndingOfEndList =
+      deepestEndPointOfEndList.IsSet() &&
+      deepestEndPointOfEndList.EqualsOrIsBefore(aRangeToDelete.EndRef());
+
+  EditorRawDOMRange newRangeToDelete;
+  // If all over the list element at start boundary is selected, we should
+  // shrink the range to start from the first list item to avoid to delete
+  // all list items.
+  if (!startListElementIsEmpty && rangeStartsFromBeginningOfStartList &&
+      rangeEndsByEndingOfStartListOrLater) {
+    newRangeToDelete.SetStart(EditorRawDOMPoint(
+        deepestStartPointOfStartList.ContainerAs<nsIContent>(), 0u));
+  }
+  // If all over the list element at end boundary is selected, and...
+  if (!endListElementIsEmpty && rangeEndsByEndingOfEndList) {
+    // If the range starts before the range at end boundary of the range,
+    // we want to delete the list completely, thus, we should extend the
+    // range to contain the list element.
+    if (aRangeToDelete.StartRef().IsBefore(
+            EditorRawDOMPoint(endListElement, 0u))) {
+      newRangeToDelete.SetEnd(EditorRawDOMPoint::After(*endListElement));
+      MOZ_ASSERT_IF(newRangeToDelete.StartRef().IsSet(),
+                    newRangeToDelete.IsPositionedAndValid());
+    }
+    // Otherwise, if the range starts in the end list element, we shouldn't
+    // delete the list.  Therefore, we should shrink the range to end by end
+    // of the last list item element to avoid to delete all list items.
+    else {
+      newRangeToDelete.SetEnd(EditorRawDOMPoint::AtEndOf(
+          *deepestEndPointOfEndList.ContainerAs<nsIContent>()));
+      MOZ_ASSERT_IF(newRangeToDelete.StartRef().IsSet(),
+                    newRangeToDelete.IsPositionedAndValid());
+    }
+  }
+
+  if (!newRangeToDelete.StartRef().IsSet() &&
+      !newRangeToDelete.EndRef().IsSet()) {
+    return EditorRawDOMRange();
+  }
+
+  if (!newRangeToDelete.StartRef().IsSet()) {
+    newRangeToDelete.SetStart(aRangeToDelete.StartRef());
+    MOZ_ASSERT(newRangeToDelete.IsPositionedAndValid());
+  }
+  if (!newRangeToDelete.EndRef().IsSet()) {
+    newRangeToDelete.SetEnd(aRangeToDelete.EndRef());
+    MOZ_ASSERT(newRangeToDelete.IsPositionedAndValid());
+  }
+
+  return newRangeToDelete;
+}
+
+}  // namespace mozilla
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