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diff --git a/editor/libeditor/ChangeStyleTransaction.h b/editor/libeditor/ChangeStyleTransaction.h
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+++ b/editor/libeditor/ChangeStyleTransaction.h
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+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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/. */
+
+#ifndef ChangeStyleTransaction_h
+#define ChangeStyleTransaction_h
+
+#include "EditTransactionBase.h"  // base class
+
+#include "nsCOMPtr.h"                      // nsCOMPtr members
+#include "nsCycleCollectionParticipant.h"  // various macros
+#include "nsString.h"                      // nsString members
+
+class nsAtom;
+class nsStyledElement;
+
+namespace mozilla {
+
+namespace dom {
+class Element;
+}  // namespace dom
+
+/**
+ * A transaction that changes the value of a CSS inline style of a content
+ * node.  This transaction covers add, remove, and change a property's value.
+ */
+class ChangeStyleTransaction final : public EditTransactionBase {
+ protected:
+  ChangeStyleTransaction(nsStyledElement& aStyledElement, nsAtom& aProperty,
+                         const nsAString& aValue, bool aRemove);
+
+ public:
+  /**
+   * Creates a change style transaction.  This never returns nullptr.
+   *
+   * @param aStyledElement  The node whose style attribute will be changed.
+   * @param aProperty       The name of the property to change.
+   * @param aValue          New value for aProperty.
+   */
+  static already_AddRefed<ChangeStyleTransaction> Create(
+      nsStyledElement& aStyledElement, nsAtom& aProperty,
+      const nsAString& aValue);
+
+  /**
+   * Creates a change style transaction.  This never returns nullptr.
+   *
+   * @param aStyledElement  The node whose style attribute will be changed.
+   * @param aProperty       The name of the property to change.
+   * @param aValue          The value to remove from aProperty.
+   */
+  static already_AddRefed<ChangeStyleTransaction> CreateToRemove(
+      nsStyledElement& aStyledElement, nsAtom& aProperty,
+      const nsAString& aValue);
+
+  NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(ChangeStyleTransaction,
+                                           EditTransactionBase)
+
+  NS_DECL_ISUPPORTS_INHERITED
+
+  NS_DECL_EDITTRANSACTIONBASE
+  NS_DECL_EDITTRANSACTIONBASE_GETASMETHODS_OVERRIDE(ChangeStyleTransaction)
+
+  MOZ_CAN_RUN_SCRIPT NS_IMETHOD RedoTransaction() override;
+
+  /**
+   * Returns true if the list of white-space separated values contains aValue
+   *
+   * @param aValueList      [IN] a list of white-space separated values
+   * @param aValue          [IN] the value to look for in the list
+   * @return                true if the value is in the list of values
+   */
+  static bool ValueIncludes(const nsACString& aValueList,
+                            const nsACString& aValue);
+
+  friend std::ostream& operator<<(std::ostream& aStream,
+                                  const ChangeStyleTransaction& aTransaction);
+
+ private:
+  virtual ~ChangeStyleTransaction() = default;
+
+  /**
+   * Build new text-decoration value to set/remove specific values to/from the
+   * rule which already has aCurrentValues.
+   */
+  void BuildTextDecorationValueToSet(const nsACString& aCurrentValues,
+                                     const nsACString& aAddingValues,
+                                     nsACString& aOutValues);
+  void BuildTextDecorationValueToRemove(const nsACString& aCurrentValues,
+                                        const nsACString& aRemovingValues,
+                                        nsACString& aOutValues);
+
+  /**
+   * Helper method for above methods.
+   */
+  void BuildTextDecorationValue(bool aUnderline, bool aOverline,
+                                bool aLineThrough, nsACString& aOutValues);
+
+  /**
+   * If the boolean is true and if the value is not the empty string,
+   * set the property in the transaction to that value; if the value
+   * is empty, remove the property from element's styles. If the boolean
+   * is false, just remove the style attribute.
+   */
+  MOZ_CAN_RUN_SCRIPT nsresult SetStyle(bool aAttributeWasSet,
+                                       nsACString& aValue);
+
+  // The element to operate upon.
+  RefPtr<nsStyledElement> mStyledElement;
+
+  // The CSS property to change.
+  RefPtr<nsAtom> mProperty;
+
+  // The value to set the property to (ignored if mRemoveProperty==true).
+  nsCString mValue;
+
+  // The value to set the property to for undo.
+  nsCString mUndoValue;
+  // The value to set the property to for redo.
+  nsCString mRedoValue;
+
+  // true if the operation is to remove mProperty from mElement.
+  bool mRemoveProperty;
+
+  // True if the style attribute was present and not empty before DoTransaction.
+  bool mUndoAttributeWasSet;
+  // True if the style attribute is present and not empty after DoTransaction.
+  bool mRedoAttributeWasSet;
+};
+
+}  // namespace mozilla
+
+#endif  // #ifndef ChangeStyleTransaction_h