Adding upstream version 124.0.1.upstream/124.0.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

52 files changed, 8770 insertions, 0 deletions

diff --git a/dom/xslt/xpath/XPathEvaluator.cpp b/dom/xslt/xpath/XPathEvaluator.cpp
new file mode 100644
index 0000000000..269ea98ff6
--- /dev/null
+++ b/dom/xslt/xpath/XPathEvaluator.cpp
@@ -0,0 +1,187 @@
+/* -*- Mode: C++; tab-width: 4; 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/. */
+
+#include "mozilla/dom/XPathEvaluator.h"
+
+#include <utility>
+
+#include "XPathResult.h"
+#include "mozilla/UniquePtrExtensions.h"
+#include "mozilla/dom/BindingUtils.h"
+#include "mozilla/dom/Document.h"
+#include "mozilla/dom/XPathEvaluatorBinding.h"
+#include "mozilla/dom/XPathExpression.h"
+#include "mozilla/dom/XPathNSResolverBinding.h"
+#include "nsAtom.h"
+#include "nsCOMPtr.h"
+#include "nsContentCID.h"
+#include "nsContentUtils.h"
+#include "nsDOMString.h"
+#include "nsError.h"
+#include "nsNameSpaceManager.h"
+#include "txExpr.h"
+#include "txExprParser.h"
+#include "txIXPathContext.h"
+#include "txURIUtils.h"
+
+namespace mozilla::dom {
+
+// txIParseContext implementation
+class XPathEvaluatorParseContext : public txIParseContext {
+ public:
+  XPathEvaluatorParseContext(XPathNSResolver* aResolver, bool aIsCaseSensitive)
+      : mResolver(aResolver),
+        mResolverNode(nullptr),
+        mLastError(NS_OK),
+        mIsCaseSensitive(aIsCaseSensitive) {}
+  XPathEvaluatorParseContext(nsINode* aResolver, bool aIsCaseSensitive)
+      : mResolver(nullptr),
+        mResolverNode(aResolver),
+        mLastError(NS_OK),
+        mIsCaseSensitive(aIsCaseSensitive) {}
+
+  nsresult getError() { return mLastError; }
+
+  nsresult resolveNamespacePrefix(nsAtom* aPrefix, int32_t& aID) override;
+  nsresult resolveFunctionCall(nsAtom* aName, int32_t aID,
+                               FunctionCall** aFunction) override;
+  bool caseInsensitiveNameTests() override;
+  void SetErrorOffset(uint32_t aOffset) override;
+
+ private:
+  XPathNSResolver* mResolver;
+  nsINode* mResolverNode;
+  nsresult mLastError;
+  bool mIsCaseSensitive;
+};
+
+XPathEvaluator::XPathEvaluator(Document* aDocument) : mDocument(aDocument) {}
+
+XPathEvaluator::~XPathEvaluator() = default;
+
+UniquePtr<XPathExpression> XPathEvaluator::CreateExpression(
+    const nsAString& aExpression, XPathNSResolver* aResolver,
+    ErrorResult& aRv) {
+  nsCOMPtr<Document> doc(mDocument);
+  XPathEvaluatorParseContext pContext(aResolver,
+                                      !(doc && doc->IsHTMLDocument()));
+  return CreateExpression(aExpression, &pContext, doc, aRv);
+}
+
+UniquePtr<XPathExpression> XPathEvaluator::CreateExpression(
+    const nsAString& aExpression, nsINode* aResolver, ErrorResult& aRv) {
+  nsCOMPtr<Document> doc(mDocument);
+  XPathEvaluatorParseContext pContext(aResolver,
+                                      !(doc && doc->IsHTMLDocument()));
+  return CreateExpression(aExpression, &pContext, doc, aRv);
+}
+
+UniquePtr<XPathExpression> XPathEvaluator::CreateExpression(
+    const nsAString& aExpression, txIParseContext* aContext,
+    Document* aDocument, ErrorResult& aRv) {
+  if (!mRecycler) {
+    mRecycler = new txResultRecycler;
+  }
+
+  UniquePtr<Expr> expression;
+  aRv = txExprParser::createExpr(PromiseFlatString(aExpression), aContext,
+                                 getter_Transfers(expression));
+  if (aRv.Failed()) {
+    if (!aRv.ErrorCodeIs(NS_ERROR_DOM_NAMESPACE_ERR)) {
+      aRv.SuppressException();
+      aRv.ThrowSyntaxError("The expression is not a legal expression");
+    }
+
+    return nullptr;
+  }
+
+  return MakeUnique<XPathExpression>(std::move(expression), mRecycler,
+                                     aDocument);
+}
+
+bool XPathEvaluator::WrapObject(JSContext* aCx,
+                                JS::Handle<JSObject*> aGivenProto,
+                                JS::MutableHandle<JSObject*> aReflector) {
+  return dom::XPathEvaluator_Binding::Wrap(aCx, this, aGivenProto, aReflector);
+}
+
+/* static */
+UniquePtr<XPathEvaluator> XPathEvaluator::Constructor(
+    const GlobalObject& aGlobal) {
+  return MakeUnique<XPathEvaluator>(nullptr);
+}
+
+already_AddRefed<XPathResult> XPathEvaluator::Evaluate(
+    JSContext* aCx, const nsAString& aExpression, nsINode& aContextNode,
+    XPathNSResolver* aResolver, uint16_t aType, JS::Handle<JSObject*> aResult,
+    ErrorResult& rv) {
+  UniquePtr<XPathExpression> expression(
+      CreateExpression(aExpression, aResolver, rv));
+  if (rv.Failed()) {
+    return nullptr;
+  }
+  return expression->Evaluate(aCx, aContextNode, aType, aResult, rv);
+}
+
+/*
+ * Implementation of txIParseContext private to XPathEvaluator, based on a
+ * XPathNSResolver
+ */
+
+nsresult XPathEvaluatorParseContext::resolveNamespacePrefix(nsAtom* aPrefix,
+                                                            int32_t& aID) {
+  aID = kNameSpaceID_Unknown;
+
+  if (!mResolver && !mResolverNode) {
+    return NS_ERROR_DOM_NAMESPACE_ERR;
+  }
+
+  nsAutoString prefix;
+  if (aPrefix) {
+    aPrefix->ToString(prefix);
+  }
+
+  nsAutoString ns;
+  if (mResolver) {
+    ErrorResult rv;
+    mResolver->LookupNamespaceURI(prefix, ns, rv);
+    if (rv.Failed()) {
+      return rv.StealNSResult();
+    }
+  } else {
+    if (aPrefix == nsGkAtoms::xml) {
+      ns.AssignLiteral("http://www.w3.org/XML/1998/namespace");
+    } else {
+      mResolverNode->LookupNamespaceURI(prefix, ns);
+    }
+  }
+
+  if (DOMStringIsNull(ns)) {
+    return NS_ERROR_DOM_NAMESPACE_ERR;
+  }
+
+  if (ns.IsEmpty()) {
+    aID = kNameSpaceID_None;
+
+    return NS_OK;
+  }
+
+  // get the namespaceID for the URI
+  return nsNameSpaceManager::GetInstance()->RegisterNameSpace(ns, aID);
+}
+
+nsresult XPathEvaluatorParseContext::resolveFunctionCall(nsAtom* aName,
+                                                         int32_t aID,
+                                                         FunctionCall** aFn) {
+  return NS_ERROR_XPATH_UNKNOWN_FUNCTION;
+}
+
+bool XPathEvaluatorParseContext::caseInsensitiveNameTests() {
+  return !mIsCaseSensitive;
+}
+
+void XPathEvaluatorParseContext::SetErrorOffset(uint32_t aOffset) {}
+
+}  // namespace mozilla::dom
diff --git a/dom/xslt/xpath/XPathEvaluator.h b/dom/xslt/xpath/XPathEvaluator.h
new file mode 100644
index 0000000000..dbf79373b9
--- /dev/null
+++ b/dom/xslt/xpath/XPathEvaluator.h
@@ -0,0 +1,65 @@
+/* -*- Mode: C++; tab-width: 4; 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 mozilla_dom_XPathEvaluator_h
+#define mozilla_dom_XPathEvaluator_h
+
+#include "mozilla/dom/NonRefcountedDOMObject.h"
+#include "nsString.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/dom/Document.h"
+
+class nsINode;
+class txIParseContext;
+class txResultRecycler;
+
+namespace mozilla {
+class ErrorResult;
+
+namespace dom {
+
+class GlobalObject;
+class XPathExpression;
+class XPathNSResolver;
+class XPathResult;
+
+/**
+ * A class for evaluating an XPath expression string
+ */
+class XPathEvaluator final : public NonRefcountedDOMObject {
+ public:
+  explicit XPathEvaluator(Document* aDocument = nullptr);
+  ~XPathEvaluator();
+
+  // WebIDL API
+  bool WrapObject(JSContext* aCx, JS::Handle<JSObject*> aGivenProto,
+                  JS::MutableHandle<JSObject*> aReflector);
+  Document* GetParentObject() { return mDocument; }
+  static UniquePtr<XPathEvaluator> Constructor(const GlobalObject& aGlobal);
+  UniquePtr<XPathExpression> CreateExpression(const nsAString& aExpression,
+                                              XPathNSResolver* aResolver,
+                                              ErrorResult& rv);
+  UniquePtr<XPathExpression> CreateExpression(const nsAString& aExpression,
+                                              nsINode* aResolver,
+                                              ErrorResult& aRv);
+  UniquePtr<XPathExpression> CreateExpression(const nsAString& aExpression,
+                                              txIParseContext* aContext,
+                                              Document* aDocument,
+                                              ErrorResult& aRv);
+  nsINode* CreateNSResolver(nsINode& aNodeResolver) { return &aNodeResolver; }
+  already_AddRefed<XPathResult> Evaluate(
+      JSContext* aCx, const nsAString& aExpression, nsINode& aContextNode,
+      XPathNSResolver* aResolver, uint16_t aType, JS::Handle<JSObject*> aResult,
+      ErrorResult& rv);
+
+ private:
+  WeakPtr<Document> mDocument;
+  RefPtr<txResultRecycler> mRecycler;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif /* mozilla_dom_XPathEvaluator_h */
diff --git a/dom/xslt/xpath/XPathExpression.cpp b/dom/xslt/xpath/XPathExpression.cpp
new file mode 100644
index 0000000000..0706763d79
--- /dev/null
+++ b/dom/xslt/xpath/XPathExpression.cpp
@@ -0,0 +1,210 @@
+/* -*- Mode: C++; tab-width: 4; 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/. */
+
+#include "XPathExpression.h"
+
+#include <utility>
+
+#include "XPathResult.h"
+#include "mozilla/dom/BindingUtils.h"
+#include "mozilla/dom/Text.h"
+#include "mozilla/dom/XPathResultBinding.h"
+#include "nsError.h"
+#include "nsINode.h"
+#include "txExpr.h"
+#include "txExprResult.h"
+#include "txIXPathContext.h"
+#include "txURIUtils.h"
+#include "txXPathTreeWalker.h"
+
+namespace mozilla::dom {
+
+class EvalContextImpl : public txIEvalContext {
+ public:
+  EvalContextImpl(const txXPathNode& aContextNode, uint32_t aContextPosition,
+                  uint32_t aContextSize, txResultRecycler* aRecycler)
+      : mContextNode(aContextNode),
+        mContextPosition(aContextPosition),
+        mContextSize(aContextSize),
+        mLastError(NS_OK),
+        mRecycler(aRecycler) {}
+
+  nsresult getError() { return mLastError; }
+
+  TX_DECL_EVAL_CONTEXT;
+
+ private:
+  const txXPathNode& mContextNode;
+  uint32_t mContextPosition;
+  uint32_t mContextSize;
+  nsresult mLastError;
+  RefPtr<txResultRecycler> mRecycler;
+};
+
+XPathExpression::XPathExpression(UniquePtr<Expr>&& aExpression,
+                                 txResultRecycler* aRecycler,
+                                 Document* aDocument)
+    : mExpression(std::move(aExpression)),
+      mRecycler(aRecycler),
+      mDocument(do_GetWeakReference(aDocument)),
+      mCheckDocument(aDocument != nullptr) {}
+
+XPathExpression::~XPathExpression() = default;
+
+already_AddRefed<XPathResult> XPathExpression::EvaluateWithContext(
+    JSContext* aCx, nsINode& aContextNode, uint32_t aContextPosition,
+    uint32_t aContextSize, uint16_t aType, JS::Handle<JSObject*> aInResult,
+    ErrorResult& aRv) {
+  RefPtr<XPathResult> inResult;
+  if (aInResult) {
+    nsresult rv = UNWRAP_OBJECT(XPathResult, aInResult, inResult);
+    if (NS_FAILED(rv) && rv != NS_ERROR_XPC_BAD_CONVERT_JS) {
+      aRv.Throw(rv);
+      return nullptr;
+    }
+  }
+
+  return EvaluateWithContext(aContextNode, aContextPosition, aContextSize,
+                             aType, inResult, aRv);
+}
+
+already_AddRefed<XPathResult> XPathExpression::EvaluateWithContext(
+    nsINode& aContextNode, uint32_t aContextPosition, uint32_t aContextSize,
+    uint16_t aType, XPathResult* aInResult, ErrorResult& aRv) {
+  if (aContextPosition > aContextSize) {
+    aRv.Throw(NS_ERROR_FAILURE);
+    return nullptr;
+  }
+
+  if (aType > XPathResult_Binding::FIRST_ORDERED_NODE_TYPE) {
+    aRv.Throw(NS_ERROR_DOM_NOT_SUPPORTED_ERR);
+    return nullptr;
+  }
+
+  if (!nsContentUtils::LegacyIsCallerNativeCode() &&
+      !nsContentUtils::CanCallerAccess(&aContextNode)) {
+    aRv.Throw(NS_ERROR_DOM_SECURITY_ERR);
+    return nullptr;
+  }
+
+  if (mCheckDocument) {
+    nsCOMPtr<Document> doc = do_QueryReferent(mDocument);
+    if (doc != aContextNode.OwnerDoc()) {
+      aRv.Throw(NS_ERROR_DOM_WRONG_DOCUMENT_ERR);
+      return nullptr;
+    }
+  }
+
+  uint16_t nodeType = aContextNode.NodeType();
+
+  if (nodeType == nsINode::TEXT_NODE ||
+      nodeType == nsINode::CDATA_SECTION_NODE) {
+    Text* textNode = aContextNode.GetAsText();
+    MOZ_ASSERT(textNode);
+
+    uint32_t textLength = textNode->Length();
+    if (textLength == 0) {
+      aRv.Throw(NS_ERROR_DOM_NOT_SUPPORTED_ERR);
+      return nullptr;
+    }
+
+    // XXX Need to get logical XPath text node for CDATASection
+    //     and Text nodes.
+  } else if (nodeType != nsINode::DOCUMENT_NODE &&
+             nodeType != nsINode::ELEMENT_NODE &&
+             nodeType != nsINode::ATTRIBUTE_NODE &&
+             nodeType != nsINode::COMMENT_NODE &&
+             nodeType != nsINode::PROCESSING_INSTRUCTION_NODE) {
+    aRv.Throw(NS_ERROR_DOM_NOT_SUPPORTED_ERR);
+    return nullptr;
+  }
+
+  UniquePtr<txXPathNode> contextNode(
+      txXPathNativeNode::createXPathNode(&aContextNode));
+  if (!contextNode) {
+    aRv.Throw(NS_ERROR_FAILURE);
+    return nullptr;
+  }
+
+  EvalContextImpl eContext(*contextNode, aContextPosition, aContextSize,
+                           mRecycler);
+  RefPtr<txAExprResult> exprResult;
+  aRv = mExpression->evaluate(&eContext, getter_AddRefs(exprResult));
+  if (aRv.Failed()) {
+    return nullptr;
+  }
+
+  uint16_t resultType = aType;
+  if (aType == XPathResult::ANY_TYPE) {
+    short exprResultType = exprResult->getResultType();
+    switch (exprResultType) {
+      case txAExprResult::NUMBER:
+        resultType = XPathResult::NUMBER_TYPE;
+        break;
+      case txAExprResult::STRING:
+        resultType = XPathResult::STRING_TYPE;
+        break;
+      case txAExprResult::BOOLEAN:
+        resultType = XPathResult::BOOLEAN_TYPE;
+        break;
+      case txAExprResult::NODESET:
+        resultType = XPathResult::UNORDERED_NODE_ITERATOR_TYPE;
+        break;
+      case txAExprResult::RESULT_TREE_FRAGMENT:
+        aRv.Throw(NS_ERROR_FAILURE);
+        return nullptr;
+    }
+  }
+
+  RefPtr<XPathResult> xpathResult = aInResult;
+  if (!xpathResult) {
+    xpathResult = new XPathResult(&aContextNode);
+  }
+
+  xpathResult->SetExprResult(exprResult, resultType, &aContextNode, aRv);
+  if (aRv.Failed()) {
+    return nullptr;
+  }
+
+  return xpathResult.forget();
+}
+
+/*
+ * Implementation of the txIEvalContext private to XPathExpression
+ * EvalContextImpl bases on only one context node and no variables
+ */
+
+nsresult EvalContextImpl::getVariable(int32_t aNamespace, nsAtom* aLName,
+                                      txAExprResult*& aResult) {
+  aResult = 0;
+  return NS_ERROR_INVALID_ARG;
+}
+
+nsresult EvalContextImpl::isStripSpaceAllowed(const txXPathNode& aNode,
+                                              bool& aAllowed) {
+  aAllowed = false;
+
+  return NS_OK;
+}
+
+void* EvalContextImpl::getPrivateContext() {
+  // we don't have a private context here.
+  return nullptr;
+}
+
+txResultRecycler* EvalContextImpl::recycler() { return mRecycler; }
+
+void EvalContextImpl::receiveError(const nsAString& aMsg, nsresult aRes) {
+  mLastError = aRes;
+  // forward aMsg to console service?
+}
+
+const txXPathNode& EvalContextImpl::getContextNode() { return mContextNode; }
+
+uint32_t EvalContextImpl::size() { return mContextSize; }
+
+uint32_t EvalContextImpl::position() { return mContextPosition; }
+
+}  // namespace mozilla::dom
diff --git a/dom/xslt/xpath/XPathExpression.h b/dom/xslt/xpath/XPathExpression.h
new file mode 100644
index 0000000000..e041649395
--- /dev/null
+++ b/dom/xslt/xpath/XPathExpression.h
@@ -0,0 +1,68 @@
+/* -*- Mode: C++; tab-width: 4; 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 mozilla_dom_XPathExpression_h
+#define mozilla_dom_XPathExpression_h
+
+#include "nsCycleCollectionParticipant.h"
+#include "nsIWeakReferenceUtils.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/dom/NonRefcountedDOMObject.h"
+#include "mozilla/dom/XPathExpressionBinding.h"
+#include "mozilla/UniquePtr.h"
+
+class Expr;
+
+class nsINode;
+class txResultRecycler;
+
+namespace mozilla::dom {
+
+class Document;
+class XPathResult;
+
+/**
+ * A class for evaluating an XPath expression string
+ */
+class XPathExpression final : public NonRefcountedDOMObject {
+ public:
+  XPathExpression(mozilla::UniquePtr<Expr>&& aExpression,
+                  txResultRecycler* aRecycler, Document* aDocument);
+  ~XPathExpression();
+
+  bool WrapObject(JSContext* aCx, JS::Handle<JSObject*> aGivenProto,
+                  JS::MutableHandle<JSObject*> aReflector) {
+    return XPathExpression_Binding::Wrap(aCx, this, aGivenProto, aReflector);
+  }
+
+  already_AddRefed<XPathResult> Evaluate(JSContext* aCx, nsINode& aContextNode,
+                                         uint16_t aType,
+                                         JS::Handle<JSObject*> aInResult,
+                                         ErrorResult& aRv) {
+    return EvaluateWithContext(aCx, aContextNode, 1, 1, aType, aInResult, aRv);
+  }
+  already_AddRefed<XPathResult> EvaluateWithContext(
+      JSContext* aCx, nsINode& aContextNode, uint32_t aContextPosition,
+      uint32_t aContextSize, uint16_t aType, JS::Handle<JSObject*> aInResult,
+      ErrorResult& aRv);
+  already_AddRefed<XPathResult> Evaluate(nsINode& aContextNode, uint16_t aType,
+                                         XPathResult* aInResult,
+                                         ErrorResult& aRv) {
+    return EvaluateWithContext(aContextNode, 1, 1, aType, aInResult, aRv);
+  }
+  already_AddRefed<XPathResult> EvaluateWithContext(
+      nsINode& aContextNode, uint32_t aContextPosition, uint32_t aContextSize,
+      uint16_t aType, XPathResult* aInResult, ErrorResult& aRv);
+
+ private:
+  mozilla::UniquePtr<Expr> mExpression;
+  RefPtr<txResultRecycler> mRecycler;
+  nsWeakPtr mDocument;
+  bool mCheckDocument;
+};
+
+}  // namespace mozilla::dom
+
+#endif /* mozilla_dom_XPathExpression_h */
diff --git a/dom/xslt/xpath/XPathResult.cpp b/dom/xslt/xpath/XPathResult.cpp
new file mode 100644
index 0000000000..091a83528f
--- /dev/null
+++ b/dom/xslt/xpath/XPathResult.cpp
@@ -0,0 +1,264 @@
+/* -*- Mode: C++; tab-width: 4; 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/. */
+
+#include "XPathResult.h"
+#include "txExprResult.h"
+#include "txNodeSet.h"
+#include "nsError.h"
+#include "mozilla/dom/Attr.h"
+#include "mozilla/dom/Element.h"
+#include "nsDOMString.h"
+#include "txXPathTreeWalker.h"
+#include "nsCycleCollectionParticipant.h"
+#include "mozilla/dom/XPathResultBinding.h"
+
+namespace mozilla::dom {
+
+XPathResult::XPathResult(nsINode* aParent)
+    : mParent(aParent),
+      mDocument(nullptr),
+      mCurrentPos(0),
+      mResultType(ANY_TYPE),
+      mInvalidIteratorState(true),
+      mBooleanResult(false),
+      mNumberResult(0) {}
+
+XPathResult::XPathResult(const XPathResult& aResult)
+    : mParent(aResult.mParent),
+      mResult(aResult.mResult),
+      mResultNodes(aResult.mResultNodes.Clone()),
+      mDocument(aResult.mDocument),
+      mContextNode(aResult.mContextNode),
+      mCurrentPos(0),
+      mResultType(aResult.mResultType),
+      mInvalidIteratorState(aResult.mInvalidIteratorState),
+      mBooleanResult(aResult.mBooleanResult),
+      mNumberResult(aResult.mNumberResult),
+      mStringResult(aResult.mStringResult) {
+  if (mDocument) {
+    mDocument->AddMutationObserver(this);
+  }
+}
+
+XPathResult::~XPathResult() { RemoveObserver(); }
+
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(XPathResult)
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(XPathResult)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mParent) { tmp->RemoveObserver(); }
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mDocument)
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(XPathResult)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mParent)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mDocument)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mResultNodes)
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(XPathResult)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(XPathResult)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(XPathResult)
+  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
+  NS_INTERFACE_MAP_ENTRY(nsIMutationObserver)
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+JSObject* XPathResult::WrapObject(JSContext* aCx,
+                                  JS::Handle<JSObject*> aGivenProto) {
+  return XPathResult_Binding::Wrap(aCx, this, aGivenProto);
+}
+
+void XPathResult::RemoveObserver() {
+  if (mDocument) {
+    mDocument->RemoveMutationObserver(this);
+  }
+}
+
+nsINode* XPathResult::IterateNext(ErrorResult& aRv) {
+  if (!isIterator()) {
+    aRv.ThrowTypeError("Result is not an iterator");
+    return nullptr;
+  }
+
+  if (mDocument) {
+    mDocument->FlushPendingNotifications(FlushType::Content);
+  }
+
+  if (mInvalidIteratorState) {
+    aRv.ThrowInvalidStateError(
+        "The document has been mutated since the result was returned");
+    return nullptr;
+  }
+
+  return mResultNodes.SafeElementAt(mCurrentPos++);
+}
+
+void XPathResult::NodeWillBeDestroyed(nsINode* aNode) {
+  nsCOMPtr<nsIMutationObserver> kungFuDeathGrip(this);
+  // Set to null to avoid unregistring unnecessarily
+  mDocument = nullptr;
+  Invalidate(aNode->IsContent() ? aNode->AsContent() : nullptr);
+}
+
+void XPathResult::CharacterDataChanged(nsIContent* aContent,
+                                       const CharacterDataChangeInfo&) {
+  Invalidate(aContent);
+}
+
+void XPathResult::AttributeChanged(Element* aElement, int32_t aNameSpaceID,
+                                   nsAtom* aAttribute, int32_t aModType,
+                                   const nsAttrValue* aOldValue) {
+  Invalidate(aElement);
+}
+
+void XPathResult::ContentAppended(nsIContent* aFirstNewContent) {
+  Invalidate(aFirstNewContent->GetParent());
+}
+
+void XPathResult::ContentInserted(nsIContent* aChild) {
+  Invalidate(aChild->GetParent());
+}
+
+void XPathResult::ContentRemoved(nsIContent* aChild,
+                                 nsIContent* aPreviousSibling) {
+  Invalidate(aChild->GetParent());
+}
+
+void XPathResult::SetExprResult(txAExprResult* aExprResult,
+                                uint16_t aResultType, nsINode* aContextNode,
+                                ErrorResult& aRv) {
+  MOZ_ASSERT(aExprResult);
+
+  if ((isSnapshot(aResultType) || isIterator(aResultType) ||
+       isNode(aResultType)) &&
+      aExprResult->getResultType() != txAExprResult::NODESET) {
+    // The DOM spec doesn't really say what should happen when reusing an
+    // XPathResult and an error is thrown. Let's not touch the XPathResult
+    // in that case.
+    aRv.ThrowTypeError("Result type mismatch");
+    return;
+  }
+
+  mResultType = aResultType;
+  mContextNode = do_GetWeakReference(aContextNode);
+
+  if (mDocument) {
+    mDocument->RemoveMutationObserver(this);
+    mDocument = nullptr;
+  }
+
+  mResultNodes.Clear();
+
+  // XXX This will keep the recycler alive, should we clear it?
+  mResult = aExprResult;
+  switch (mResultType) {
+    case BOOLEAN_TYPE: {
+      mBooleanResult = mResult->booleanValue();
+      break;
+    }
+    case NUMBER_TYPE: {
+      mNumberResult = mResult->numberValue();
+      break;
+    }
+    case STRING_TYPE: {
+      mResult->stringValue(mStringResult);
+      break;
+    }
+    default: {
+      MOZ_ASSERT(isNode() || isIterator() || isSnapshot());
+    }
+  }
+
+  if (aExprResult->getResultType() == txAExprResult::NODESET) {
+    txNodeSet* nodeSet = static_cast<txNodeSet*>(aExprResult);
+    int32_t i, count = nodeSet->size();
+    for (i = 0; i < count; ++i) {
+      nsINode* node = txXPathNativeNode::getNode(nodeSet->get(i));
+      mResultNodes.AppendElement(node);
+    }
+
+    if (count > 0) {
+      mResult = nullptr;
+    }
+  }
+
+  if (!isIterator()) {
+    return;
+  }
+
+  mCurrentPos = 0;
+  mInvalidIteratorState = false;
+
+  if (!mResultNodes.IsEmpty()) {
+    // If we support the document() function in DOM-XPath we need to
+    // observe all documents that we have resultnodes in.
+    mDocument = mResultNodes[0]->OwnerDoc();
+    NS_ASSERTION(mDocument, "We need a document!");
+    if (mDocument) {
+      mDocument->AddMutationObserver(this);
+    }
+  }
+}
+
+void XPathResult::Invalidate(const nsIContent* aChangeRoot) {
+  nsCOMPtr<nsINode> contextNode = do_QueryReferent(mContextNode);
+  // If the changes are happening in a different anonymous trees, no
+  // invalidation should happen.
+  if (contextNode && aChangeRoot &&
+      !nsContentUtils::IsInSameAnonymousTree(contextNode, aChangeRoot)) {
+    return;
+  }
+
+  mInvalidIteratorState = true;
+  // Make sure nulling out mDocument is the last thing we do.
+  if (mDocument) {
+    mDocument->RemoveMutationObserver(this);
+    mDocument = nullptr;
+  }
+}
+
+nsresult XPathResult::GetExprResult(txAExprResult** aExprResult) {
+  if (isIterator() && mInvalidIteratorState) {
+    return NS_ERROR_DOM_INVALID_STATE_ERR;
+  }
+
+  if (mResult) {
+    NS_ADDREF(*aExprResult = mResult);
+
+    return NS_OK;
+  }
+
+  if (mResultNodes.IsEmpty()) {
+    return NS_ERROR_DOM_INVALID_STATE_ERR;
+  }
+
+  RefPtr<txNodeSet> nodeSet = new txNodeSet(nullptr);
+  uint32_t i, count = mResultNodes.Length();
+  for (i = 0; i < count; ++i) {
+    UniquePtr<txXPathNode> node(
+        txXPathNativeNode::createXPathNode(mResultNodes[i]));
+    if (!node) {
+      return NS_ERROR_OUT_OF_MEMORY;
+    }
+
+    nodeSet->append(*node);
+  }
+
+  NS_ADDREF(*aExprResult = nodeSet);
+
+  return NS_OK;
+}
+
+already_AddRefed<XPathResult> XPathResult::Clone(ErrorResult& aError) {
+  if (isIterator() && mInvalidIteratorState) {
+    aError = NS_ERROR_DOM_INVALID_STATE_ERR;
+    return nullptr;
+  }
+
+  return do_AddRef(new XPathResult(*this));
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/xslt/xpath/XPathResult.h b/dom/xslt/xpath/XPathResult.h
new file mode 100644
index 0000000000..e073666a84
--- /dev/null
+++ b/dom/xslt/xpath/XPathResult.h
@@ -0,0 +1,156 @@
+/* -*- Mode: C++; tab-width: 4; 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 mozilla_dom_XPathResult_h
+#define mozilla_dom_XPathResult_h
+
+#include "nsStubMutationObserver.h"
+#include "nsCOMPtr.h"
+#include "nsCycleCollectionParticipant.h"
+#include "nsIWeakReferenceUtils.h"
+#include "nsTArray.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/ErrorResult.h"
+#include "nsString.h"
+#include "nsWrapperCache.h"
+#include "nsINode.h"
+
+class txAExprResult;
+
+namespace mozilla::dom {
+
+/**
+ * A class for evaluating an XPath expression string
+ */
+class XPathResult final : public nsStubMutationObserver, public nsWrapperCache {
+  ~XPathResult();
+
+ public:
+  explicit XPathResult(nsINode* aParent);
+  XPathResult(const XPathResult& aResult);
+
+  enum {
+    ANY_TYPE = 0U,
+    NUMBER_TYPE = 1U,
+    STRING_TYPE = 2U,
+    BOOLEAN_TYPE = 3U,
+    UNORDERED_NODE_ITERATOR_TYPE = 4U,
+    ORDERED_NODE_ITERATOR_TYPE = 5U,
+    UNORDERED_NODE_SNAPSHOT_TYPE = 6U,
+    ORDERED_NODE_SNAPSHOT_TYPE = 7U,
+    ANY_UNORDERED_NODE_TYPE = 8U,
+    FIRST_ORDERED_NODE_TYPE = 9U
+  };
+
+  // nsISupports interface
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(XPathResult)
+
+  virtual JSObject* WrapObject(JSContext* aCx,
+                               JS::Handle<JSObject*> aGivenProto) override;
+  nsINode* GetParentObject() const { return mParent; }
+  uint16_t ResultType() const { return mResultType; }
+  double GetNumberValue(ErrorResult& aRv) const {
+    if (mResultType != NUMBER_TYPE) {
+      aRv.ThrowTypeError("Result is not a number");
+      return 0;
+    }
+
+    return mNumberResult;
+  }
+  void GetStringValue(nsAString& aStringValue, ErrorResult& aRv) const {
+    if (mResultType != STRING_TYPE) {
+      aRv.ThrowTypeError("Result is not a string");
+      return;
+    }
+
+    aStringValue = mStringResult;
+  }
+  bool GetBooleanValue(ErrorResult& aRv) const {
+    if (mResultType != BOOLEAN_TYPE) {
+      aRv.ThrowTypeError("Result is not a boolean");
+      return false;
+    }
+
+    return mBooleanResult;
+  }
+  nsINode* GetSingleNodeValue(ErrorResult& aRv) const {
+    if (!isNode()) {
+      aRv.ThrowTypeError("Result is not a node");
+      return nullptr;
+    }
+
+    return mResultNodes.SafeElementAt(0);
+  }
+  bool InvalidIteratorState() const {
+    return isIterator() && mInvalidIteratorState;
+  }
+  uint32_t GetSnapshotLength(ErrorResult& aRv) const {
+    if (!isSnapshot()) {
+      aRv.ThrowTypeError("Result is not a snapshot");
+      return 0;
+    }
+
+    return (uint32_t)mResultNodes.Length();
+  }
+  nsINode* IterateNext(ErrorResult& aRv);
+  nsINode* SnapshotItem(uint32_t aIndex, ErrorResult& aRv) const {
+    if (!isSnapshot()) {
+      aRv.ThrowTypeError("Result is not a snapshot");
+      return nullptr;
+    }
+
+    return mResultNodes.SafeElementAt(aIndex);
+  }
+
+  // nsIMutationObserver interface
+  NS_DECL_NSIMUTATIONOBSERVER_CHARACTERDATACHANGED
+  NS_DECL_NSIMUTATIONOBSERVER_ATTRIBUTECHANGED
+  NS_DECL_NSIMUTATIONOBSERVER_CONTENTAPPENDED
+  NS_DECL_NSIMUTATIONOBSERVER_CONTENTINSERTED
+  NS_DECL_NSIMUTATIONOBSERVER_CONTENTREMOVED
+  NS_DECL_NSIMUTATIONOBSERVER_NODEWILLBEDESTROYED
+
+  void SetExprResult(txAExprResult* aExprResult, uint16_t aResultType,
+                     nsINode* aContextNode, ErrorResult& aRv);
+  nsresult GetExprResult(txAExprResult** aExprResult);
+  already_AddRefed<XPathResult> Clone(ErrorResult& aError);
+  void RemoveObserver();
+
+ private:
+  static bool isSnapshot(uint16_t aResultType) {
+    return aResultType == UNORDERED_NODE_SNAPSHOT_TYPE ||
+           aResultType == ORDERED_NODE_SNAPSHOT_TYPE;
+  }
+  static bool isIterator(uint16_t aResultType) {
+    return aResultType == UNORDERED_NODE_ITERATOR_TYPE ||
+           aResultType == ORDERED_NODE_ITERATOR_TYPE;
+  }
+  static bool isNode(uint16_t aResultType) {
+    return aResultType == FIRST_ORDERED_NODE_TYPE ||
+           aResultType == ANY_UNORDERED_NODE_TYPE;
+  }
+  bool isSnapshot() const { return isSnapshot(mResultType); }
+  bool isIterator() const { return isIterator(mResultType); }
+  bool isNode() const { return isNode(mResultType); }
+
+  void Invalidate(const nsIContent* aChangeRoot);
+
+  nsCOMPtr<nsINode> mParent;
+  RefPtr<txAExprResult> mResult;
+  nsTArray<nsCOMPtr<nsINode>> mResultNodes;
+  RefPtr<Document> mDocument;
+  nsWeakPtr mContextNode;
+  uint32_t mCurrentPos;
+  uint16_t mResultType;
+  bool mInvalidIteratorState;
+  bool mBooleanResult;
+  double mNumberResult;
+  nsString mStringResult;
+};
+
+}  // namespace mozilla::dom
+
+#endif /* mozilla_dom_XPathResult_h */
diff --git a/dom/xslt/xpath/moz.build b/dom/xslt/xpath/moz.build
new file mode 100644
index 0000000000..9cf562c0af
--- /dev/null
+++ b/dom/xslt/xpath/moz.build
@@ -0,0 +1,58 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# 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/.
+
+EXPORTS.mozilla.dom += [
+    "txIXPathContext.h",
+    "XPathEvaluator.h",
+    "XPathExpression.h",
+    "XPathResult.h",
+]
+
+UNIFIED_SOURCES += [
+    "txBooleanExpr.cpp",
+    "txBooleanResult.cpp",
+    "txCoreFunctionCall.cpp",
+    "txErrorExpr.cpp",
+    "txExpr.cpp",
+    "txExprLexer.cpp",
+    "txExprParser.cpp",
+    "txFilterExpr.cpp",
+    "txForwardContext.cpp",
+    "txFunctionCall.cpp",
+    "txLiteralExpr.cpp",
+    "txLocationStep.cpp",
+    "txMozillaXPathTreeWalker.cpp",
+    "txNamedAttributeStep.cpp",
+    "txNameTest.cpp",
+    "txNodeSet.cpp",
+    "txNodeSetContext.cpp",
+    "txNodeTypeTest.cpp",
+    "txNumberExpr.cpp",
+    "txNumberResult.cpp",
+    "txPathExpr.cpp",
+    "txPredicatedNodeTest.cpp",
+    "txPredicateList.cpp",
+    "txRelationalExpr.cpp",
+    "txResultRecycler.cpp",
+    "txRootExpr.cpp",
+    "txStringResult.cpp",
+    "txUnaryExpr.cpp",
+    "txUnionExpr.cpp",
+    "txUnionNodeTest.cpp",
+    "txVariableRefExpr.cpp",
+    "txXPathOptimizer.cpp",
+    "XPathEvaluator.cpp",
+    "XPathExpression.cpp",
+    "XPathResult.cpp",
+]
+
+LOCAL_INCLUDES += [
+    "../base",
+    "../xml",
+    "../xslt",
+]
+
+FINAL_LIBRARY = "xul"
diff --git a/dom/xslt/xpath/txBooleanExpr.cpp b/dom/xslt/xpath/txBooleanExpr.cpp
new file mode 100644
index 0000000000..0f4366ff76
--- /dev/null
+++ b/dom/xslt/xpath/txBooleanExpr.cpp
@@ -0,0 +1,78 @@
+/* -*- Mode: C++; tab-width: 4; 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/. */
+
+/**
+ * Represents a BooleanExpr, a binary expression that
+ * performs a boolean operation between its lvalue and rvalue.
+ **/
+
+#include "txExpr.h"
+#include "txIXPathContext.h"
+
+/**
+ * Evaluates this Expr based on the given context node and processor state
+ * @param context the context node for evaluation of this Expr
+ * @param ps the ContextState containing the stack information needed
+ * for evaluation
+ * @return the result of the evaluation
+ **/
+nsresult BooleanExpr::evaluate(txIEvalContext* aContext,
+                               txAExprResult** aResult) {
+  *aResult = nullptr;
+
+  bool lval;
+  nsresult rv = leftExpr->evaluateToBool(aContext, lval);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  // check for early decision
+  if (op == OR && lval) {
+    aContext->recycler()->getBoolResult(true, aResult);
+
+    return NS_OK;
+  }
+  if (op == AND && !lval) {
+    aContext->recycler()->getBoolResult(false, aResult);
+
+    return NS_OK;
+  }
+
+  bool rval;
+  rv = rightExpr->evaluateToBool(aContext, rval);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  // just use rval, since we already checked lval
+  aContext->recycler()->getBoolResult(rval, aResult);
+
+  return NS_OK;
+}  //-- evaluate
+
+TX_IMPL_EXPR_STUBS_2(BooleanExpr, BOOLEAN_RESULT, leftExpr, rightExpr)
+
+bool BooleanExpr::isSensitiveTo(ContextSensitivity aContext) {
+  return leftExpr->isSensitiveTo(aContext) ||
+         rightExpr->isSensitiveTo(aContext);
+}
+
+#ifdef TX_TO_STRING
+void BooleanExpr::toString(nsAString& str) {
+  if (leftExpr)
+    leftExpr->toString(str);
+  else
+    str.AppendLiteral("null");
+
+  switch (op) {
+    case OR:
+      str.AppendLiteral(" or ");
+      break;
+    default:
+      str.AppendLiteral(" and ");
+      break;
+  }
+  if (rightExpr)
+    rightExpr->toString(str);
+  else
+    str.AppendLiteral("null");
+}
+#endif
diff --git a/dom/xslt/xpath/txBooleanResult.cpp b/dom/xslt/xpath/txBooleanResult.cpp
new file mode 100644
index 0000000000..1d69a8c347
--- /dev/null
+++ b/dom/xslt/xpath/txBooleanResult.cpp
@@ -0,0 +1,48 @@
+/* -*- Mode: C++; tab-width: 4; 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/. */
+
+/*
+ * Boolean Expression result
+ */
+
+#include "txExprResult.h"
+
+/**
+ * Creates a new BooleanResult with the value of the given bool parameter
+ * @param boolean the bool to use for initialization of this BooleanResult's
+ * value
+ **/
+BooleanResult::BooleanResult(bool boolean) : txAExprResult(nullptr) {
+  this->value = boolean;
+}  //-- BooleanResult
+
+/*
+ * Virtual Methods from ExprResult
+ */
+
+short BooleanResult::getResultType() {
+  return txAExprResult::BOOLEAN;
+}  //-- getResultType
+
+void BooleanResult::stringValue(nsString& aResult) {
+  if (value) {
+    aResult.AppendLiteral("true");
+  } else {
+    aResult.AppendLiteral("false");
+  }
+}
+
+const nsString* BooleanResult::stringValuePointer() {
+  // In theory we could set strings containing "true" and "false" somewhere,
+  // but most stylesheets never get the stringvalue of a bool so that won't
+  // really buy us anything.
+  return nullptr;
+}
+
+bool BooleanResult::booleanValue() { return this->value; }  //-- toBoolean
+
+double BooleanResult::numberValue() {
+  return (value) ? 1.0 : 0.0;
+}  //-- toNumber
diff --git a/dom/xslt/xpath/txCoreFunctionCall.cpp b/dom/xslt/xpath/txCoreFunctionCall.cpp
new file mode 100644
index 0000000000..6e2285ed18
--- /dev/null
+++ b/dom/xslt/xpath/txCoreFunctionCall.cpp
@@ -0,0 +1,665 @@
+/* -*- Mode: C++; tab-width: 4; 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/. */
+
+#include "mozilla/ArrayUtils.h"
+#include "mozilla/FloatingPoint.h"
+
+#include "txExpr.h"
+#include "txNodeSet.h"
+#include "nsGkAtoms.h"
+#include "txIXPathContext.h"
+#include "nsWhitespaceTokenizer.h"
+#include "txXPathTreeWalker.h"
+#include <math.h>
+#include "txStringUtils.h"
+#include "txXMLUtils.h"
+
+using namespace mozilla;
+
+struct txCoreFunctionDescriptor {
+  const int8_t mMinParams;
+  const int8_t mMaxParams;
+  const Expr::ResultType mReturnType;
+  const nsStaticAtom* const mName;
+};
+
+// This must be ordered in the same order as txCoreFunctionCall::eType.
+// If you change one, change the other.
+static const txCoreFunctionDescriptor descriptTable[] = {
+    {1, 1, Expr::NUMBER_RESULT, nsGkAtoms::count},         // COUNT
+    {1, 1, Expr::NODESET_RESULT, nsGkAtoms::id},           // ID
+    {0, 0, Expr::NUMBER_RESULT, nsGkAtoms::last},          // LAST
+    {0, 1, Expr::STRING_RESULT, nsGkAtoms::localName},     // LOCAL_NAME
+    {0, 1, Expr::STRING_RESULT, nsGkAtoms::namespaceUri},  // NAMESPACE_URI
+    {0, 1, Expr::STRING_RESULT, nsGkAtoms::name},          // NAME
+    {0, 0, Expr::NUMBER_RESULT, nsGkAtoms::position},      // POSITION
+
+    {2, -1, Expr::STRING_RESULT, nsGkAtoms::concat},         // CONCAT
+    {2, 2, Expr::BOOLEAN_RESULT, nsGkAtoms::contains},       // CONTAINS
+    {0, 1, Expr::STRING_RESULT, nsGkAtoms::normalizeSpace},  // NORMALIZE_SPACE
+    {2, 2, Expr::BOOLEAN_RESULT, nsGkAtoms::startsWith},     // STARTS_WITH
+    {0, 1, Expr::STRING_RESULT, nsGkAtoms::string},          // STRING
+    {0, 1, Expr::NUMBER_RESULT, nsGkAtoms::stringLength},    // STRING_LENGTH
+    {2, 3, Expr::STRING_RESULT, nsGkAtoms::substring},       // SUBSTRING
+    {2, 2, Expr::STRING_RESULT, nsGkAtoms::substringAfter},  // SUBSTRING_AFTER
+    {2, 2, Expr::STRING_RESULT,
+     nsGkAtoms::substringBefore},                       // SUBSTRING_BEFORE
+    {3, 3, Expr::STRING_RESULT, nsGkAtoms::translate},  // TRANSLATE
+
+    {0, 1, Expr::NUMBER_RESULT, nsGkAtoms::number},   // NUMBER
+    {1, 1, Expr::NUMBER_RESULT, nsGkAtoms::round},    // ROUND
+    {1, 1, Expr::NUMBER_RESULT, nsGkAtoms::floor},    // FLOOR
+    {1, 1, Expr::NUMBER_RESULT, nsGkAtoms::ceiling},  // CEILING
+    {1, 1, Expr::NUMBER_RESULT, nsGkAtoms::sum},      // SUM
+
+    {1, 1, Expr::BOOLEAN_RESULT, nsGkAtoms::boolean},  // BOOLEAN
+    {0, 0, Expr::BOOLEAN_RESULT, nsGkAtoms::_false},   // _FALSE
+    {1, 1, Expr::BOOLEAN_RESULT, nsGkAtoms::lang},     // LANG
+    {1, 1, Expr::BOOLEAN_RESULT, nsGkAtoms::_not},     // _NOT
+    {0, 0, Expr::BOOLEAN_RESULT, nsGkAtoms::_true}     // _TRUE
+};
+
+/*
+ * Evaluates this Expr based on the given context node and processor state
+ * @param context the context node for evaluation of this Expr
+ * @param ps the ContextState containing the stack information needed
+ * for evaluation
+ * @return the result of the evaluation
+ */
+nsresult txCoreFunctionCall::evaluate(txIEvalContext* aContext,
+                                      txAExprResult** aResult) {
+  *aResult = nullptr;
+
+  if (!requireParams(descriptTable[mType].mMinParams,
+                     descriptTable[mType].mMaxParams, aContext)) {
+    return NS_ERROR_XPATH_BAD_ARGUMENT_COUNT;
+  }
+
+  nsresult rv = NS_OK;
+  switch (mType) {
+    case COUNT: {
+      RefPtr<txNodeSet> nodes;
+      rv = evaluateToNodeSet(mParams[0], aContext, getter_AddRefs(nodes));
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      return aContext->recycler()->getNumberResult(nodes->size(), aResult);
+    }
+    case ID: {
+      RefPtr<txAExprResult> exprResult;
+      rv = mParams[0]->evaluate(aContext, getter_AddRefs(exprResult));
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      RefPtr<txNodeSet> resultSet;
+      rv = aContext->recycler()->getNodeSet(getter_AddRefs(resultSet));
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      txXPathTreeWalker walker(aContext->getContextNode());
+
+      if (exprResult->getResultType() == txAExprResult::NODESET) {
+        txNodeSet* nodes =
+            static_cast<txNodeSet*>(static_cast<txAExprResult*>(exprResult));
+        int32_t i;
+        for (i = 0; i < nodes->size(); ++i) {
+          nsAutoString idList;
+          txXPathNodeUtils::appendNodeValue(nodes->get(i), idList);
+          nsWhitespaceTokenizer tokenizer(idList);
+          while (tokenizer.hasMoreTokens()) {
+            if (walker.moveToElementById(tokenizer.nextToken())) {
+              resultSet->add(walker.getCurrentPosition());
+            }
+          }
+        }
+      } else {
+        nsAutoString idList;
+        exprResult->stringValue(idList);
+        nsWhitespaceTokenizer tokenizer(idList);
+        while (tokenizer.hasMoreTokens()) {
+          if (walker.moveToElementById(tokenizer.nextToken())) {
+            resultSet->add(walker.getCurrentPosition());
+          }
+        }
+      }
+
+      *aResult = resultSet;
+      NS_ADDREF(*aResult);
+
+      return NS_OK;
+    }
+    case LAST: {
+      return aContext->recycler()->getNumberResult(aContext->size(), aResult);
+    }
+    case LOCAL_NAME:
+    case NAME:
+    case NAMESPACE_URI: {
+      // Check for optional arg
+      RefPtr<txNodeSet> nodes;
+      if (!mParams.IsEmpty()) {
+        rv = evaluateToNodeSet(mParams[0], aContext, getter_AddRefs(nodes));
+        NS_ENSURE_SUCCESS(rv, rv);
+
+        if (nodes->isEmpty()) {
+          aContext->recycler()->getEmptyStringResult(aResult);
+
+          return NS_OK;
+        }
+      }
+
+      const txXPathNode& node =
+          nodes ? nodes->get(0) : aContext->getContextNode();
+      switch (mType) {
+        case LOCAL_NAME: {
+          StringResult* strRes = nullptr;
+          rv = aContext->recycler()->getStringResult(&strRes);
+          NS_ENSURE_SUCCESS(rv, rv);
+
+          *aResult = strRes;
+          txXPathNodeUtils::getLocalName(node, strRes->mValue);
+
+          return NS_OK;
+        }
+        case NAMESPACE_URI: {
+          StringResult* strRes = nullptr;
+          rv = aContext->recycler()->getStringResult(&strRes);
+          NS_ENSURE_SUCCESS(rv, rv);
+
+          *aResult = strRes;
+          txXPathNodeUtils::getNamespaceURI(node, strRes->mValue);
+
+          return NS_OK;
+        }
+        case NAME: {
+          // XXX Namespace: namespaces have a name
+          if (txXPathNodeUtils::isAttribute(node) ||
+              txXPathNodeUtils::isElement(node) ||
+              txXPathNodeUtils::isProcessingInstruction(node)) {
+            StringResult* strRes = nullptr;
+            rv = aContext->recycler()->getStringResult(&strRes);
+            NS_ENSURE_SUCCESS(rv, rv);
+
+            *aResult = strRes;
+            txXPathNodeUtils::getNodeName(node, strRes->mValue);
+          } else {
+            aContext->recycler()->getEmptyStringResult(aResult);
+          }
+
+          return NS_OK;
+        }
+        default: {
+          MOZ_CRASH("Unexpected mType?!");
+        }
+      }
+      MOZ_CRASH("Inner mType switch should have returned!");
+    }
+    case POSITION: {
+      return aContext->recycler()->getNumberResult(aContext->position(),
+                                                   aResult);
+    }
+
+      // String functions
+
+    case CONCAT: {
+      RefPtr<StringResult> strRes;
+      rv = aContext->recycler()->getStringResult(getter_AddRefs(strRes));
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      uint32_t i, len = mParams.Length();
+      for (i = 0; i < len; ++i) {
+        rv = mParams[i]->evaluateToString(aContext, strRes->mValue);
+        NS_ENSURE_SUCCESS(rv, rv);
+      }
+
+      NS_ADDREF(*aResult = strRes);
+
+      return NS_OK;
+    }
+    case CONTAINS: {
+      nsAutoString arg2;
+      rv = mParams[1]->evaluateToString(aContext, arg2);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      if (arg2.IsEmpty()) {
+        aContext->recycler()->getBoolResult(true, aResult);
+      } else {
+        nsAutoString arg1;
+        rv = mParams[0]->evaluateToString(aContext, arg1);
+        NS_ENSURE_SUCCESS(rv, rv);
+
+        aContext->recycler()->getBoolResult(FindInReadable(arg2, arg1),
+                                            aResult);
+      }
+
+      return NS_OK;
+    }
+    case NORMALIZE_SPACE: {
+      nsAutoString resultStr;
+      if (!mParams.IsEmpty()) {
+        rv = mParams[0]->evaluateToString(aContext, resultStr);
+        NS_ENSURE_SUCCESS(rv, rv);
+      } else {
+        txXPathNodeUtils::appendNodeValue(aContext->getContextNode(),
+                                          resultStr);
+      }
+
+      RefPtr<StringResult> strRes;
+      rv = aContext->recycler()->getStringResult(getter_AddRefs(strRes));
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      bool addSpace = false;
+      bool first = true;
+      strRes->mValue.SetCapacity(resultStr.Length());
+      char16_t c;
+      uint32_t src;
+      for (src = 0; src < resultStr.Length(); src++) {
+        c = resultStr.CharAt(src);
+        if (XMLUtils::isWhitespace(c)) {
+          addSpace = true;
+        } else {
+          if (addSpace && !first) strRes->mValue.Append(char16_t(' '));
+
+          strRes->mValue.Append(c);
+          addSpace = false;
+          first = false;
+        }
+      }
+      *aResult = strRes;
+      NS_ADDREF(*aResult);
+
+      return NS_OK;
+    }
+    case STARTS_WITH: {
+      nsAutoString arg2;
+      rv = mParams[1]->evaluateToString(aContext, arg2);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      bool result = false;
+      if (arg2.IsEmpty()) {
+        result = true;
+      } else {
+        nsAutoString arg1;
+        rv = mParams[0]->evaluateToString(aContext, arg1);
+        NS_ENSURE_SUCCESS(rv, rv);
+
+        result = StringBeginsWith(arg1, arg2);
+      }
+
+      aContext->recycler()->getBoolResult(result, aResult);
+
+      return NS_OK;
+    }
+    case STRING: {
+      RefPtr<StringResult> strRes;
+      rv = aContext->recycler()->getStringResult(getter_AddRefs(strRes));
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      if (!mParams.IsEmpty()) {
+        rv = mParams[0]->evaluateToString(aContext, strRes->mValue);
+        NS_ENSURE_SUCCESS(rv, rv);
+      } else {
+        txXPathNodeUtils::appendNodeValue(aContext->getContextNode(),
+                                          strRes->mValue);
+      }
+
+      NS_ADDREF(*aResult = strRes);
+
+      return NS_OK;
+    }
+    case STRING_LENGTH: {
+      nsAutoString resultStr;
+      if (!mParams.IsEmpty()) {
+        rv = mParams[0]->evaluateToString(aContext, resultStr);
+        NS_ENSURE_SUCCESS(rv, rv);
+      } else {
+        txXPathNodeUtils::appendNodeValue(aContext->getContextNode(),
+                                          resultStr);
+      }
+      rv = aContext->recycler()->getNumberResult(resultStr.Length(), aResult);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      return NS_OK;
+    }
+    case SUBSTRING: {
+      nsAutoString src;
+      rv = mParams[0]->evaluateToString(aContext, src);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      double start;
+      rv = evaluateToNumber(mParams[1], aContext, &start);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      // check for NaN or +/-Inf
+      if (std::isnan(start) || std::isinf(start) ||
+          start >= src.Length() + 0.5) {
+        aContext->recycler()->getEmptyStringResult(aResult);
+
+        return NS_OK;
+      }
+
+      start = floor(start + 0.5) - 1;
+
+      double end;
+      if (mParams.Length() == 3) {
+        rv = evaluateToNumber(mParams[2], aContext, &end);
+        NS_ENSURE_SUCCESS(rv, rv);
+
+        end += start;
+        if (std::isnan(end) || end < 0) {
+          aContext->recycler()->getEmptyStringResult(aResult);
+
+          return NS_OK;
+        }
+
+        if (end > src.Length())
+          end = src.Length();
+        else
+          end = floor(end + 0.5);
+      } else {
+        end = src.Length();
+      }
+
+      if (start < 0) start = 0;
+
+      if (start > end) {
+        aContext->recycler()->getEmptyStringResult(aResult);
+
+        return NS_OK;
+      }
+
+      return aContext->recycler()->getStringResult(
+          Substring(src, (uint32_t)start, (uint32_t)(end - start)), aResult);
+    }
+    case SUBSTRING_AFTER: {
+      nsAutoString arg1;
+      rv = mParams[0]->evaluateToString(aContext, arg1);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      nsAutoString arg2;
+      rv = mParams[1]->evaluateToString(aContext, arg2);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      if (arg2.IsEmpty()) {
+        return aContext->recycler()->getStringResult(arg1, aResult);
+      }
+
+      int32_t idx = arg1.Find(arg2);
+      if (idx == kNotFound) {
+        aContext->recycler()->getEmptyStringResult(aResult);
+
+        return NS_OK;
+      }
+
+      const nsAString& result = Substring(arg1, idx + arg2.Length());
+      return aContext->recycler()->getStringResult(result, aResult);
+    }
+    case SUBSTRING_BEFORE: {
+      nsAutoString arg2;
+      rv = mParams[1]->evaluateToString(aContext, arg2);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      if (arg2.IsEmpty()) {
+        aContext->recycler()->getEmptyStringResult(aResult);
+
+        return NS_OK;
+      }
+
+      nsAutoString arg1;
+      rv = mParams[0]->evaluateToString(aContext, arg1);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      int32_t idx = arg1.Find(arg2);
+      if (idx == kNotFound) {
+        aContext->recycler()->getEmptyStringResult(aResult);
+
+        return NS_OK;
+      }
+
+      return aContext->recycler()->getStringResult(StringHead(arg1, idx),
+                                                   aResult);
+    }
+    case TRANSLATE: {
+      nsAutoString src;
+      rv = mParams[0]->evaluateToString(aContext, src);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      if (src.IsEmpty()) {
+        aContext->recycler()->getEmptyStringResult(aResult);
+
+        return NS_OK;
+      }
+
+      RefPtr<StringResult> strRes;
+      rv = aContext->recycler()->getStringResult(getter_AddRefs(strRes));
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      strRes->mValue.SetCapacity(src.Length());
+
+      nsAutoString oldChars, newChars;
+      rv = mParams[1]->evaluateToString(aContext, oldChars);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      rv = mParams[2]->evaluateToString(aContext, newChars);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      uint32_t i;
+      int32_t newCharsLength = (int32_t)newChars.Length();
+      for (i = 0; i < src.Length(); i++) {
+        int32_t idx = oldChars.FindChar(src.CharAt(i));
+        if (idx != kNotFound) {
+          if (idx < newCharsLength)
+            strRes->mValue.Append(newChars.CharAt((uint32_t)idx));
+        } else {
+          strRes->mValue.Append(src.CharAt(i));
+        }
+      }
+
+      NS_ADDREF(*aResult = strRes);
+
+      return NS_OK;
+    }
+
+      // Number functions
+
+    case NUMBER: {
+      double res;
+      if (!mParams.IsEmpty()) {
+        rv = evaluateToNumber(mParams[0], aContext, &res);
+        NS_ENSURE_SUCCESS(rv, rv);
+      } else {
+        nsAutoString resultStr;
+        txXPathNodeUtils::appendNodeValue(aContext->getContextNode(),
+                                          resultStr);
+        res = txDouble::toDouble(resultStr);
+      }
+      return aContext->recycler()->getNumberResult(res, aResult);
+    }
+    case ROUND: {
+      double dbl;
+      rv = evaluateToNumber(mParams[0], aContext, &dbl);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      if (std::isfinite(dbl)) {
+        if (mozilla::IsNegative(dbl) && dbl >= -0.5) {
+          dbl *= 0;
+        } else {
+          dbl = floor(dbl + 0.5);
+        }
+      }
+
+      return aContext->recycler()->getNumberResult(dbl, aResult);
+    }
+    case FLOOR: {
+      double dbl;
+      rv = evaluateToNumber(mParams[0], aContext, &dbl);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      if (std::isfinite(dbl) && !mozilla::IsNegativeZero(dbl)) dbl = floor(dbl);
+
+      return aContext->recycler()->getNumberResult(dbl, aResult);
+    }
+    case CEILING: {
+      double dbl;
+      rv = evaluateToNumber(mParams[0], aContext, &dbl);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      if (std::isfinite(dbl)) {
+        if (mozilla::IsNegative(dbl) && dbl > -1)
+          dbl *= 0;
+        else
+          dbl = ceil(dbl);
+      }
+
+      return aContext->recycler()->getNumberResult(dbl, aResult);
+    }
+    case SUM: {
+      RefPtr<txNodeSet> nodes;
+      nsresult rv =
+          evaluateToNodeSet(mParams[0], aContext, getter_AddRefs(nodes));
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      double res = 0;
+      int32_t i;
+      for (i = 0; i < nodes->size(); ++i) {
+        nsAutoString resultStr;
+        txXPathNodeUtils::appendNodeValue(nodes->get(i), resultStr);
+        res += txDouble::toDouble(resultStr);
+      }
+      return aContext->recycler()->getNumberResult(res, aResult);
+    }
+
+      // Boolean functions
+
+    case BOOLEAN: {
+      bool result;
+      nsresult rv = mParams[0]->evaluateToBool(aContext, result);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      aContext->recycler()->getBoolResult(result, aResult);
+
+      return NS_OK;
+    }
+    case _FALSE: {
+      aContext->recycler()->getBoolResult(false, aResult);
+
+      return NS_OK;
+    }
+    case LANG: {
+      txXPathTreeWalker walker(aContext->getContextNode());
+
+      nsAutoString lang;
+      bool found;
+      do {
+        found = walker.getAttr(nsGkAtoms::lang, kNameSpaceID_XML, lang);
+      } while (!found && walker.moveToParent());
+
+      if (!found) {
+        aContext->recycler()->getBoolResult(false, aResult);
+
+        return NS_OK;
+      }
+
+      nsAutoString arg;
+      rv = mParams[0]->evaluateToString(aContext, arg);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      bool result =
+          StringBeginsWith(lang, arg, nsCaseInsensitiveStringComparator) &&
+          (lang.Length() == arg.Length() || lang.CharAt(arg.Length()) == '-');
+
+      aContext->recycler()->getBoolResult(result, aResult);
+
+      return NS_OK;
+    }
+    case _NOT: {
+      bool result;
+      rv = mParams[0]->evaluateToBool(aContext, result);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      aContext->recycler()->getBoolResult(!result, aResult);
+
+      return NS_OK;
+    }
+    case _TRUE: {
+      aContext->recycler()->getBoolResult(true, aResult);
+
+      return NS_OK;
+    }
+  }
+
+  aContext->receiveError(u"Internal error"_ns, NS_ERROR_UNEXPECTED);
+  return NS_ERROR_UNEXPECTED;
+}
+
+Expr::ResultType txCoreFunctionCall::getReturnType() {
+  return descriptTable[mType].mReturnType;
+}
+
+bool txCoreFunctionCall::isSensitiveTo(ContextSensitivity aContext) {
+  switch (mType) {
+    case COUNT:
+    case CONCAT:
+    case CONTAINS:
+    case STARTS_WITH:
+    case SUBSTRING:
+    case SUBSTRING_AFTER:
+    case SUBSTRING_BEFORE:
+    case TRANSLATE:
+    case ROUND:
+    case FLOOR:
+    case CEILING:
+    case SUM:
+    case BOOLEAN:
+    case _NOT:
+    case _FALSE:
+    case _TRUE: {
+      return argsSensitiveTo(aContext);
+    }
+    case ID: {
+      return (aContext & NODE_CONTEXT) || argsSensitiveTo(aContext);
+    }
+    case LAST: {
+      return !!(aContext & SIZE_CONTEXT);
+    }
+    case LOCAL_NAME:
+    case NAME:
+    case NAMESPACE_URI:
+    case NORMALIZE_SPACE:
+    case STRING:
+    case STRING_LENGTH:
+    case NUMBER: {
+      if (mParams.IsEmpty()) {
+        return !!(aContext & NODE_CONTEXT);
+      }
+      return argsSensitiveTo(aContext);
+    }
+    case POSITION: {
+      return !!(aContext & POSITION_CONTEXT);
+    }
+    case LANG: {
+      return (aContext & NODE_CONTEXT) || argsSensitiveTo(aContext);
+    }
+  }
+
+  MOZ_ASSERT_UNREACHABLE("how'd we get here?");
+  return true;
+}
+
+// static
+bool txCoreFunctionCall::getTypeFromAtom(nsAtom* aName, eType& aType) {
+  uint32_t i;
+  for (i = 0; i < ArrayLength(descriptTable); ++i) {
+    if (aName == descriptTable[i].mName) {
+      aType = static_cast<eType>(i);
+
+      return true;
+    }
+  }
+
+  return false;
+}
+
+#ifdef TX_TO_STRING
+void txCoreFunctionCall::appendName(nsAString& aDest) {
+  aDest.Append(descriptTable[mType].mName->GetUTF16String());
+}
+#endif
diff --git a/dom/xslt/xpath/txErrorExpr.cpp b/dom/xslt/xpath/txErrorExpr.cpp
new file mode 100644
index 0000000000..806b324259
--- /dev/null
+++ b/dom/xslt/xpath/txErrorExpr.cpp
@@ -0,0 +1,35 @@
+/* -*- Mode: C++; tab-width: 4; 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/. */
+
+#include "nsError.h"
+#include "txExpr.h"
+#include "nsString.h"
+#include "txIXPathContext.h"
+
+nsresult txErrorExpr::evaluate(txIEvalContext* aContext,
+                               txAExprResult** aResult) {
+  *aResult = nullptr;
+
+  nsAutoString err(u"Invalid expression evaluated"_ns);
+#ifdef TX_TO_STRING
+  err.AppendLiteral(": ");
+  toString(err);
+#endif
+  aContext->receiveError(err, NS_ERROR_XPATH_INVALID_EXPRESSION_EVALUATED);
+
+  return NS_ERROR_XPATH_INVALID_EXPRESSION_EVALUATED;
+}
+
+TX_IMPL_EXPR_STUBS_0(txErrorExpr, ANY_RESULT)
+
+bool txErrorExpr::isSensitiveTo(ContextSensitivity aContext) {
+  // It doesn't really matter what we return here, but it might
+  // be a good idea to try to keep this as unoptimizable as possible
+  return true;
+}
+
+#ifdef TX_TO_STRING
+void txErrorExpr::toString(nsAString& aStr) { aStr.Append(mStr); }
+#endif
diff --git a/dom/xslt/xpath/txExpr.cpp b/dom/xslt/xpath/txExpr.cpp
new file mode 100644
index 0000000000..d5ea774f62
--- /dev/null
+++ b/dom/xslt/xpath/txExpr.cpp
@@ -0,0 +1,26 @@
+/* -*- Mode: C++; tab-width: 4; 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/. */
+
+#include "txExpr.h"
+
+nsresult Expr::evaluateToBool(txIEvalContext* aContext, bool& aResult) {
+  RefPtr<txAExprResult> exprRes;
+  nsresult rv = evaluate(aContext, getter_AddRefs(exprRes));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  aResult = exprRes->booleanValue();
+
+  return NS_OK;
+}
+
+nsresult Expr::evaluateToString(txIEvalContext* aContext, nsString& aResult) {
+  RefPtr<txAExprResult> exprRes;
+  nsresult rv = evaluate(aContext, getter_AddRefs(exprRes));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  exprRes->stringValue(aResult);
+
+  return NS_OK;
+}
diff --git a/dom/xslt/xpath/txExpr.h b/dom/xslt/xpath/txExpr.h
new file mode 100644
index 0000000000..2622a3fe9f
--- /dev/null
+++ b/dom/xslt/xpath/txExpr.h
@@ -0,0 +1,847 @@
+/* -*- Mode: C++; tab-width: 4; 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 TRANSFRMX_EXPR_H
+#define TRANSFRMX_EXPR_H
+
+#include "mozilla/Attributes.h"
+#include "mozilla/UniquePtr.h"
+#include "txExprResult.h"
+#include "txCore.h"
+#include "nsString.h"
+#include "txOwningArray.h"
+#include "nsAtom.h"
+
+#ifdef DEBUG
+#  define TX_TO_STRING
+#endif
+
+/*
+  XPath class definitions.
+  Much of this code was ported from XSL:P.
+*/
+
+class nsAtom;
+class txIMatchContext;
+class txIEvalContext;
+class txNodeSet;
+class txXPathNode;
+class txXPathTreeWalker;
+
+/**
+ * A Base Class for all XSL Expressions
+ **/
+class Expr {
+ public:
+  MOZ_COUNTED_DEFAULT_CTOR(Expr)
+  MOZ_COUNTED_DTOR_VIRTUAL(Expr)
+
+  /**
+   * Evaluates this Expr based on the given context node and processor state
+   * @param context the context node for evaluation of this Expr
+   * @param ps the ContextState containing the stack information needed
+   * for evaluation
+   * @return the result of the evaluation
+   **/
+  virtual nsresult evaluate(txIEvalContext* aContext,
+                            txAExprResult** aResult) = 0;
+
+  /**
+   * Returns the type of this expression.
+   */
+  enum ExprType {
+    LOCATIONSTEP_EXPR,
+    PATH_EXPR,
+    UNION_EXPR,
+    LITERAL_EXPR,
+    OTHER_EXPR
+  };
+  virtual ExprType getType() { return OTHER_EXPR; }
+
+  /**
+   * Returns the type or types of results this Expr return.
+   */
+  using ResultType = uint16_t;
+  enum {
+    NODESET_RESULT = 0x01,
+    BOOLEAN_RESULT = 0x02,
+    NUMBER_RESULT = 0x04,
+    STRING_RESULT = 0x08,
+    RTF_RESULT = 0x10,
+    ANY_RESULT = 0xFFFF
+  };
+  virtual ResultType getReturnType() = 0;
+  bool canReturnType(ResultType aType) {
+    return (getReturnType() & aType) != 0;
+  }
+
+  using ContextSensitivity = uint16_t;
+  enum {
+    NO_CONTEXT = 0x00,
+    NODE_CONTEXT = 0x01,
+    POSITION_CONTEXT = 0x02,
+    SIZE_CONTEXT = 0x04,
+    NODESET_CONTEXT = POSITION_CONTEXT | SIZE_CONTEXT,
+    VARIABLES_CONTEXT = 0x08,
+    PRIVATE_CONTEXT = 0x10,
+    ANY_CONTEXT = 0xFFFF
+  };
+
+  /**
+   * Returns true if this expression is sensitive to *any* of
+   * the requested contexts in aContexts.
+   */
+  virtual bool isSensitiveTo(ContextSensitivity aContexts) = 0;
+
+  /**
+   * Returns sub-expression at given position
+   */
+  virtual Expr* getSubExprAt(uint32_t aPos) = 0;
+
+  /**
+   * Replace sub-expression at given position. Does not delete the old
+   * expression, that is the responsibility of the caller.
+   */
+  virtual void setSubExprAt(uint32_t aPos, Expr* aExpr) = 0;
+
+  virtual nsresult evaluateToBool(txIEvalContext* aContext, bool& aResult);
+
+  virtual nsresult evaluateToString(txIEvalContext* aContext,
+                                    nsString& aResult);
+
+#ifdef TX_TO_STRING
+  /**
+   * Returns the String representation of this Expr.
+   * @param dest the String to use when creating the String
+   * representation. The String representation will be appended to
+   * any data in the destination String, to allow cascading calls to
+   * other #toString() methods for Expressions.
+   * @return the String representation of this Expr.
+   **/
+  virtual void toString(nsAString& str) = 0;
+#endif
+};  //-- Expr
+
+#ifdef TX_TO_STRING
+#  define TX_DECL_TOSTRING void toString(nsAString& aDest) override;
+#  define TX_DECL_APPENDNAME void appendName(nsAString& aDest) override;
+#else
+#  define TX_DECL_TOSTRING
+#  define TX_DECL_APPENDNAME
+#endif
+
+#define TX_DECL_EXPR_BASE                                              \
+  nsresult evaluate(txIEvalContext* aContext, txAExprResult** aResult) \
+      override;                                                        \
+  ResultType getReturnType() override;                                 \
+  bool isSensitiveTo(ContextSensitivity aContexts) override;
+
+#define TX_DECL_EXPR                          \
+  TX_DECL_EXPR_BASE                           \
+  TX_DECL_TOSTRING                            \
+  Expr* getSubExprAt(uint32_t aPos) override; \
+  void setSubExprAt(uint32_t aPos, Expr* aExpr) override;
+
+#define TX_DECL_OPTIMIZABLE_EXPR \
+  TX_DECL_EXPR                   \
+  ExprType getType() override;
+
+#define TX_DECL_FUNCTION \
+  TX_DECL_APPENDNAME     \
+  TX_DECL_EXPR_BASE
+
+#define TX_IMPL_EXPR_STUBS_BASE(_class, _ReturnType) \
+  Expr::ResultType _class::getReturnType() { return _ReturnType; }
+
+#define TX_IMPL_EXPR_STUBS_0(_class, _ReturnType)               \
+  TX_IMPL_EXPR_STUBS_BASE(_class, _ReturnType)                  \
+  Expr* _class::getSubExprAt(uint32_t aPos) { return nullptr; } \
+  void _class::setSubExprAt(uint32_t aPos, Expr* aExpr) {       \
+    MOZ_ASSERT_UNREACHABLE("setting bad subexpression index");  \
+  }
+
+#define TX_IMPL_EXPR_STUBS_1(_class, _ReturnType, _Expr1)      \
+  TX_IMPL_EXPR_STUBS_BASE(_class, _ReturnType)                 \
+  Expr* _class::getSubExprAt(uint32_t aPos) {                  \
+    if (aPos == 0) {                                           \
+      return _Expr1.get();                                     \
+    }                                                          \
+    return nullptr;                                            \
+  }                                                            \
+  void _class::setSubExprAt(uint32_t aPos, Expr* aExpr) {      \
+    NS_ASSERTION(aPos < 1, "setting bad subexpression index"); \
+    mozilla::Unused << _Expr1.release();                       \
+    _Expr1 = mozilla::WrapUnique(aExpr);                       \
+  }
+
+#define TX_IMPL_EXPR_STUBS_2(_class, _ReturnType, _Expr1, _Expr2) \
+  TX_IMPL_EXPR_STUBS_BASE(_class, _ReturnType)                    \
+  Expr* _class::getSubExprAt(uint32_t aPos) {                     \
+    switch (aPos) {                                               \
+      case 0:                                                     \
+        return _Expr1.get();                                      \
+      case 1:                                                     \
+        return _Expr2.get();                                      \
+      default:                                                    \
+        break;                                                    \
+    }                                                             \
+    return nullptr;                                               \
+  }                                                               \
+  void _class::setSubExprAt(uint32_t aPos, Expr* aExpr) {         \
+    NS_ASSERTION(aPos < 2, "setting bad subexpression index");    \
+    if (aPos == 0) {                                              \
+      mozilla::Unused << _Expr1.release();                        \
+      _Expr1 = mozilla::WrapUnique(aExpr);                        \
+    } else {                                                      \
+      mozilla::Unused << _Expr2.release();                        \
+      _Expr2 = mozilla::WrapUnique(aExpr);                        \
+    }                                                             \
+  }
+
+#define TX_IMPL_EXPR_STUBS_LIST(_class, _ReturnType, _ExprList) \
+  TX_IMPL_EXPR_STUBS_BASE(_class, _ReturnType)                  \
+  Expr* _class::getSubExprAt(uint32_t aPos) {                   \
+    return _ExprList.SafeElementAt(aPos);                       \
+  }                                                             \
+  void _class::setSubExprAt(uint32_t aPos, Expr* aExpr) {       \
+    NS_ASSERTION(aPos < _ExprList.Length(),                     \
+                 "setting bad subexpression index");            \
+    _ExprList[aPos] = aExpr;                                    \
+  }
+
+/**
+ * This class represents a FunctionCall as defined by the XPath 1.0
+ * Recommendation.
+ **/
+class FunctionCall : public Expr {
+ public:
+  /**
+   * Adds the given parameter to this FunctionCall's parameter list.
+   * The ownership of the given Expr is passed over to the FunctionCall,
+   * even on failure.
+   * @param aExpr the Expr to add to this FunctionCall's parameter list
+   */
+  void addParam(Expr* aExpr) { mParams.AppendElement(aExpr); }
+
+  /**
+   * Check if the number of parameters falls within a range.
+   *
+   * @param aParamCountMin minimum number of required parameters.
+   * @param aParamCountMax maximum number of parameters. If aParamCountMax
+   *                       is negative the maximum number is not checked.
+   * @return boolean representing whether the number of parameters falls
+   *         within the expected range or not.
+   *
+   * XXX txIEvalContext should be txIParseContest, bug 143291
+   */
+  virtual bool requireParams(int32_t aParamCountMin, int32_t aParamCountMax,
+                             txIEvalContext* aContext);
+
+  TX_DECL_TOSTRING
+  Expr* getSubExprAt(uint32_t aPos) override;
+  void setSubExprAt(uint32_t aPos, Expr* aExpr) override;
+
+ protected:
+  txOwningArray<Expr> mParams;
+
+  /*
+   * Evaluates the given Expression and converts its result to a number.
+   */
+  static nsresult evaluateToNumber(Expr* aExpr, txIEvalContext* aContext,
+                                   double* aResult);
+
+  /*
+   * Evaluates the given Expression and converts its result to a NodeSet.
+   * If the result is not a NodeSet an error is returned.
+   */
+  static nsresult evaluateToNodeSet(Expr* aExpr, txIEvalContext* aContext,
+                                    txNodeSet** aResult);
+
+  /**
+   * Returns true if any argument is sensitive to the given context.
+   */
+  bool argsSensitiveTo(ContextSensitivity aContexts);
+
+#ifdef TX_TO_STRING
+  /*
+   * Appends the name of the function to `aStr`.
+   */
+  virtual void appendName(nsAString& aStr) = 0;
+#endif
+};
+
+class txCoreFunctionCall : public FunctionCall {
+ public:
+  // This must be ordered in the same order as descriptTable in
+  // txCoreFunctionCall.cpp. If you change one, change the other.
+  enum eType {
+    COUNT = 0,      // count()
+    ID,             // id()
+    LAST,           // last()
+    LOCAL_NAME,     // local-name()
+    NAMESPACE_URI,  // namespace-uri()
+    NAME,           // name()
+    POSITION,       // position()
+
+    CONCAT,            // concat()
+    CONTAINS,          // contains()
+    NORMALIZE_SPACE,   // normalize-space()
+    STARTS_WITH,       // starts-with()
+    STRING,            // string()
+    STRING_LENGTH,     // string-length()
+    SUBSTRING,         // substring()
+    SUBSTRING_AFTER,   // substring-after()
+    SUBSTRING_BEFORE,  // substring-before()
+    TRANSLATE,         // translate()
+
+    NUMBER,   // number()
+    ROUND,    // round()
+    FLOOR,    // floor()
+    CEILING,  // ceiling()
+    SUM,      // sum()
+
+    BOOLEAN,  // boolean()
+    _FALSE,   // false()
+    LANG,     // lang()
+    _NOT,     // not()
+    _TRUE     // true()
+  };
+
+  /*
+   * Creates a txCoreFunctionCall of the given type
+   */
+  explicit txCoreFunctionCall(eType aType) : mType(aType) {}
+
+  TX_DECL_FUNCTION
+
+  static bool getTypeFromAtom(nsAtom* aName, eType& aType);
+
+ private:
+  eType mType;
+};
+
+/*
+ * This class represents a NodeTest as defined by the XPath spec
+ */
+class txNodeTest {
+ public:
+  MOZ_COUNTED_DEFAULT_CTOR(txNodeTest)
+  MOZ_COUNTED_DTOR_VIRTUAL(txNodeTest)
+
+  /*
+   * Virtual methods
+   * pretty much a txPattern, but not supposed to be used
+   * standalone. The NodeTest node() is different to the
+   * Pattern "node()" (document node isn't matched)
+   */
+  virtual nsresult matches(const txXPathNode& aNode, txIMatchContext* aContext,
+                           bool& aMatched) = 0;
+  virtual double getDefaultPriority() = 0;
+
+  /**
+   * Returns the type of this nodetest.
+   */
+  enum NodeTestType { NAME_TEST, NODETYPE_TEST, OTHER_TEST };
+  virtual NodeTestType getType() { return OTHER_TEST; }
+
+  /**
+   * Returns true if this expression is sensitive to *any* of
+   * the requested flags.
+   */
+  virtual bool isSensitiveTo(Expr::ContextSensitivity aContext) = 0;
+
+#ifdef TX_TO_STRING
+  virtual void toString(nsAString& aDest) = 0;
+#endif
+};
+
+#define TX_DECL_NODE_TEST                                               \
+  TX_DECL_TOSTRING                                                      \
+  nsresult matches(const txXPathNode& aNode, txIMatchContext* aContext, \
+                   bool& aMatched) override;                            \
+  double getDefaultPriority() override;                                 \
+  bool isSensitiveTo(Expr::ContextSensitivity aContext) override;
+
+/*
+ * This class represents a NameTest as defined by the XPath spec
+ */
+class txNameTest : public txNodeTest {
+ public:
+  /*
+   * Creates a new txNameTest with the given type and the given
+   * principal node type
+   */
+  txNameTest(nsAtom* aPrefix, nsAtom* aLocalName, int32_t aNSID,
+             uint16_t aNodeType);
+
+  NodeTestType getType() override;
+
+  TX_DECL_NODE_TEST
+
+  RefPtr<nsAtom> mPrefix;
+  RefPtr<nsAtom> mLocalName;
+  int32_t mNamespace;
+
+ private:
+  uint16_t mNodeType;
+};
+
+/*
+ * This class represents a NodeType as defined by the XPath spec
+ */
+class txNodeTypeTest : public txNodeTest {
+ public:
+  enum NodeType { COMMENT_TYPE, TEXT_TYPE, PI_TYPE, NODE_TYPE };
+
+  /*
+   * Creates a new txNodeTypeTest of the given type
+   */
+  explicit txNodeTypeTest(NodeType aNodeType) : mNodeType(aNodeType) {}
+
+  /*
+   * Sets the name of the node to match. Only availible for pi nodes
+   */
+  void setNodeName(const nsAString& aName) { mNodeName = NS_Atomize(aName); }
+
+  NodeType getNodeTestType() { return mNodeType; }
+
+  NodeTestType getType() override;
+
+  TX_DECL_NODE_TEST
+
+ private:
+  NodeType mNodeType;
+  RefPtr<nsAtom> mNodeName;
+};
+
+/**
+ * Class representing a nodetest combined with a predicate. May only be used
+ * if the predicate is not sensitive to the context-nodelist.
+ */
+class txPredicatedNodeTest : public txNodeTest {
+ public:
+  txPredicatedNodeTest(txNodeTest* aNodeTest, Expr* aPredicate);
+  TX_DECL_NODE_TEST
+
+ private:
+  mozilla::UniquePtr<txNodeTest> mNodeTest;
+  mozilla::UniquePtr<Expr> mPredicate;
+};
+
+/**
+ * Represents an ordered list of Predicates,
+ * for use with Step and Filter Expressions
+ **/
+class PredicateList {
+ public:
+  /**
+   * Adds the given Expr to the list.
+   * The ownership of the given Expr is passed over the PredicateList,
+   * even on failure.
+   * @param aExpr the Expr to add to the list
+   */
+  void add(Expr* aExpr) {
+    NS_ASSERTION(aExpr, "missing expression");
+    mPredicates.AppendElement(aExpr);
+  }
+
+  nsresult evaluatePredicates(txNodeSet* aNodes, txIMatchContext* aContext);
+
+  /**
+   * Drops the first predicate without deleting it.
+   */
+  void dropFirst() { mPredicates.RemoveElementAt(0); }
+
+  /**
+   * returns true if this predicate list is empty
+   **/
+  bool isEmpty() { return mPredicates.IsEmpty(); }
+
+#ifdef TX_TO_STRING
+  /**
+   * Returns the String representation of this PredicateList.
+   * @param dest the String to use when creating the String
+   * representation. The String representation will be appended to
+   * any data in the destination String, to allow cascading calls to
+   * other #toString() methods for Expressions.
+   * @return the String representation of this PredicateList.
+   **/
+  void toString(nsAString& dest);
+#endif
+
+ protected:
+  bool isSensitiveTo(Expr::ContextSensitivity aContext);
+  Expr* getSubExprAt(uint32_t aPos) { return mPredicates.SafeElementAt(aPos); }
+  void setSubExprAt(uint32_t aPos, Expr* aExpr) {
+    NS_ASSERTION(aPos < mPredicates.Length(),
+                 "setting bad subexpression index");
+    mPredicates[aPos] = aExpr;
+  }
+
+  //-- list of predicates
+  txOwningArray<Expr> mPredicates;
+};  //-- PredicateList
+
+class LocationStep : public Expr, public PredicateList {
+ public:
+  enum LocationStepType {
+    ANCESTOR_AXIS = 0,
+    ANCESTOR_OR_SELF_AXIS,
+    ATTRIBUTE_AXIS,
+    CHILD_AXIS,
+    DESCENDANT_AXIS,
+    DESCENDANT_OR_SELF_AXIS,
+    FOLLOWING_AXIS,
+    FOLLOWING_SIBLING_AXIS,
+    NAMESPACE_AXIS,
+    PARENT_AXIS,
+    PRECEDING_AXIS,
+    PRECEDING_SIBLING_AXIS,
+    SELF_AXIS
+  };
+
+  /**
+   * Creates a new LocationStep using the given NodeExpr and Axis Identifier
+   * @param nodeExpr the NodeExpr to use when matching Nodes
+   * @param axisIdentifier the Axis Identifier in which to search for nodes
+   **/
+  LocationStep(txNodeTest* aNodeTest, LocationStepType aAxisIdentifier)
+      : mNodeTest(aNodeTest), mAxisIdentifier(aAxisIdentifier) {}
+
+  TX_DECL_OPTIMIZABLE_EXPR
+
+  txNodeTest* getNodeTest() { return mNodeTest.get(); }
+  void setNodeTest(txNodeTest* aNodeTest) {
+    mozilla::Unused << mNodeTest.release();
+    mNodeTest = mozilla::WrapUnique(aNodeTest);
+  }
+  LocationStepType getAxisIdentifier() { return mAxisIdentifier; }
+  void setAxisIdentifier(LocationStepType aAxisIdentifier) {
+    mAxisIdentifier = aAxisIdentifier;
+  }
+
+ private:
+  /**
+   * Append the current position of aWalker to aNodes if it matches mNodeTest,
+   * using aContext as the context for matching.
+   */
+  nsresult appendIfMatching(const txXPathTreeWalker& aWalker,
+                            txIMatchContext* aContext, txNodeSet* aNodes);
+
+  /**
+   * Append the descendants of the current position of aWalker to aNodes if
+   * they match mNodeTest, using aContext as the context for matching.
+   */
+  nsresult appendMatchingDescendants(const txXPathTreeWalker& aWalker,
+                                     txIMatchContext* aContext,
+                                     txNodeSet* aNodes);
+
+  /**
+   * Append the descendants of the current position of aWalker to aNodes in
+   * reverse order if they match mNodeTest, using aContext as the context for
+   * matching.
+   */
+  nsresult appendMatchingDescendantsRev(const txXPathTreeWalker& aWalker,
+                                        txIMatchContext* aContext,
+                                        txNodeSet* aNodes);
+
+  mozilla::UniquePtr<txNodeTest> mNodeTest;
+  LocationStepType mAxisIdentifier;
+};
+
+class FilterExpr : public Expr, public PredicateList {
+ public:
+  /**
+   * Creates a new FilterExpr using the given Expr
+   * @param expr the Expr to use for evaluation
+   */
+  explicit FilterExpr(Expr* aExpr) : expr(aExpr) {}
+
+  TX_DECL_EXPR
+
+ private:
+  mozilla::UniquePtr<Expr> expr;
+
+};  //-- FilterExpr
+
+class txLiteralExpr : public Expr {
+ public:
+  explicit txLiteralExpr(double aDbl)
+      : mValue(new NumberResult(aDbl, nullptr)) {}
+  explicit txLiteralExpr(const nsAString& aStr)
+      : mValue(new StringResult(aStr, nullptr)) {}
+  explicit txLiteralExpr(txAExprResult* aValue) : mValue(aValue) {}
+
+  TX_DECL_EXPR
+
+ private:
+  RefPtr<txAExprResult> mValue;
+};
+
+/**
+ * Represents an UnaryExpr. Returns the negative value of its expr.
+ **/
+class UnaryExpr : public Expr {
+ public:
+  explicit UnaryExpr(Expr* aExpr) : expr(aExpr) {}
+
+  TX_DECL_EXPR
+
+ private:
+  mozilla::UniquePtr<Expr> expr;
+};  //-- UnaryExpr
+
+/**
+ * Represents a BooleanExpr, a binary expression that
+ * performs a boolean operation between its lvalue and rvalue.
+ **/
+class BooleanExpr : public Expr {
+ public:
+  //-- BooleanExpr Types
+  enum _BooleanExprType { AND = 1, OR };
+
+  BooleanExpr(Expr* aLeftExpr, Expr* aRightExpr, short aOp)
+      : leftExpr(aLeftExpr), rightExpr(aRightExpr), op(aOp) {}
+
+  TX_DECL_EXPR
+
+ private:
+  mozilla::UniquePtr<Expr> leftExpr, rightExpr;
+  short op;
+};  //-- BooleanExpr
+
+/**
+ * Represents a MultiplicativeExpr, a binary expression that
+ * performs a multiplicative operation between its lvalue and rvalue:
+ *  *   : multiply
+ * mod  : modulus
+ * div  : divide
+ *
+ **/
+class txNumberExpr : public Expr {
+ public:
+  enum eOp { ADD, SUBTRACT, DIVIDE, MULTIPLY, MODULUS };
+
+  txNumberExpr(Expr* aLeftExpr, Expr* aRightExpr, eOp aOp)
+      : mLeftExpr(aLeftExpr), mRightExpr(aRightExpr), mOp(aOp) {}
+
+  TX_DECL_EXPR
+
+ private:
+  mozilla::UniquePtr<Expr> mLeftExpr, mRightExpr;
+  eOp mOp;
+};  //-- MultiplicativeExpr
+
+/**
+ * Represents a RelationalExpr, an expression that compares its lvalue
+ * to its rvalue using:
+ * =  : equal to
+ * <  : less than
+ * >  : greater than
+ * <= : less than or equal to
+ * >= : greater than or equal to
+ *
+ **/
+class RelationalExpr : public Expr {
+ public:
+  enum RelationalExprType {
+    EQUAL,
+    NOT_EQUAL,
+    LESS_THAN,
+    GREATER_THAN,
+    LESS_OR_EQUAL,
+    GREATER_OR_EQUAL
+  };
+
+  RelationalExpr(Expr* aLeftExpr, Expr* aRightExpr, RelationalExprType aOp)
+      : mLeftExpr(aLeftExpr), mRightExpr(aRightExpr), mOp(aOp) {}
+
+  TX_DECL_EXPR
+
+ private:
+  bool compareResults(txIEvalContext* aContext, txAExprResult* aLeft,
+                      txAExprResult* aRight);
+
+  mozilla::UniquePtr<Expr> mLeftExpr;
+  mozilla::UniquePtr<Expr> mRightExpr;
+  RelationalExprType mOp;
+};
+
+/**
+ * VariableRefExpr
+ * Represents a variable reference ($refname)
+ **/
+class VariableRefExpr : public Expr {
+ public:
+  VariableRefExpr(nsAtom* aPrefix, nsAtom* aLocalName, int32_t aNSID);
+
+  TX_DECL_EXPR
+
+ private:
+  RefPtr<nsAtom> mPrefix;
+  RefPtr<nsAtom> mLocalName;
+  int32_t mNamespace;
+};
+
+/**
+ *  Represents a PathExpr
+ **/
+class PathExpr : public Expr {
+ public:
+  //-- Path Operators
+  //-- RELATIVE_OP is the default
+  //-- LF, changed from static const short to enum
+  enum PathOperator { RELATIVE_OP, DESCENDANT_OP };
+
+  /**
+   * Adds the Expr to this PathExpr
+   * The ownership of the given Expr is passed over the PathExpr,
+   * even on failure.
+   * @param aExpr the Expr to add to this PathExpr
+   */
+  void addExpr(Expr* aExpr, PathOperator pathOp);
+
+  /**
+   * Removes and deletes the expression at the given index.
+   */
+  void deleteExprAt(uint32_t aPos) {
+    NS_ASSERTION(aPos < mItems.Length(), "killing bad expression index");
+    mItems.RemoveElementAt(aPos);
+  }
+
+  TX_DECL_OPTIMIZABLE_EXPR
+
+  PathOperator getPathOpAt(uint32_t aPos) {
+    NS_ASSERTION(aPos < mItems.Length(), "getting bad pathop index");
+    return mItems[aPos].pathOp;
+  }
+  void setPathOpAt(uint32_t aPos, PathOperator aPathOp) {
+    NS_ASSERTION(aPos < mItems.Length(), "setting bad pathop index");
+    mItems[aPos].pathOp = aPathOp;
+  }
+
+ private:
+  class PathExprItem {
+   public:
+    mozilla::UniquePtr<Expr> expr;
+    PathOperator pathOp;
+  };
+
+  nsTArray<PathExprItem> mItems;
+
+  /*
+   * Selects from the descendants of the context node
+   * all nodes that match the Expr
+   */
+  nsresult evalDescendants(Expr* aStep, const txXPathNode& aNode,
+                           txIMatchContext* aContext, txNodeSet* resNodes);
+};
+
+/**
+ * This class represents a RootExpr, which only matches the Document node
+ **/
+class RootExpr : public Expr {
+ public:
+  /**
+   * Creates a new RootExpr
+   */
+  RootExpr()
+#ifdef TX_TO_STRING
+      : mSerialize(true)
+#endif
+  {
+  }
+
+  TX_DECL_EXPR
+
+#ifdef TX_TO_STRING
+ public:
+  void setSerialize(bool aSerialize) { mSerialize = aSerialize; }
+
+ private:
+  // When a RootExpr is used in a PathExpr it shouldn't be serialized
+  bool mSerialize;
+#endif
+};  //-- RootExpr
+
+/**
+ *  Represents a UnionExpr
+ **/
+class UnionExpr : public Expr {
+ public:
+  /**
+   * Adds the PathExpr to this UnionExpr
+   * The ownership of the given Expr is passed over the UnionExpr,
+   * even on failure.
+   * @param aExpr the Expr to add to this UnionExpr
+   */
+  void addExpr(Expr* aExpr) { mExpressions.AppendElement(aExpr); }
+
+  /**
+   * Removes and deletes the expression at the given index.
+   */
+  void deleteExprAt(uint32_t aPos) {
+    NS_ASSERTION(aPos < mExpressions.Length(), "killing bad expression index");
+
+    delete mExpressions[aPos];
+    mExpressions.RemoveElementAt(aPos);
+  }
+
+  TX_DECL_OPTIMIZABLE_EXPR
+
+ private:
+  txOwningArray<Expr> mExpressions;
+
+};  //-- UnionExpr
+
+/**
+ * Class specializing in executing expressions like "@foo" where we are
+ * interested in different result-types, and expressions like "@foo = 'hi'"
+ */
+class txNamedAttributeStep : public Expr {
+ public:
+  txNamedAttributeStep(int32_t aNsID, nsAtom* aPrefix, nsAtom* aLocalName);
+
+  TX_DECL_EXPR
+
+ private:
+  int32_t mNamespace;
+  RefPtr<nsAtom> mPrefix;
+  RefPtr<nsAtom> mLocalName;
+};
+
+/**
+ *
+ */
+class txUnionNodeTest : public txNodeTest {
+ public:
+  void addNodeTest(txNodeTest* aNodeTest) {
+    mNodeTests.AppendElement(aNodeTest);
+  }
+
+  TX_DECL_NODE_TEST
+
+ private:
+  txOwningArray<txNodeTest> mNodeTests;
+};
+
+/**
+ *  Expression that failed to parse
+ */
+class txErrorExpr : public Expr {
+ public:
+#ifdef TX_TO_STRING
+  explicit txErrorExpr(const nsAString& aStr) : mStr(aStr) {}
+#endif
+
+  TX_DECL_EXPR
+
+#ifdef TX_TO_STRING
+ private:
+  nsString mStr;
+#endif
+};
+
+#endif
diff --git a/dom/xslt/xpath/txExprLexer.cpp b/dom/xslt/xpath/txExprLexer.cpp
new file mode 100644
index 0000000000..391dc2e875
--- /dev/null
+++ b/dom/xslt/xpath/txExprLexer.cpp
@@ -0,0 +1,333 @@
+/* -*- 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/. */
+
+/**
+ * Lexical analyzer for XPath expressions
+ */
+
+#include "txExprLexer.h"
+#include "nsGkAtoms.h"
+#include "nsString.h"
+#include "nsError.h"
+#include "txXMLUtils.h"
+
+/**
+ * Creates a new ExprLexer
+ */
+txExprLexer::txExprLexer()
+    : mPosition(nullptr),
+      mCurrentItem(nullptr),
+      mFirstItem(nullptr),
+      mLastItem(nullptr),
+      mTokenCount(0) {}
+
+/**
+ * Destroys this instance of an txExprLexer
+ */
+txExprLexer::~txExprLexer() {
+  //-- delete tokens
+  Token* tok = mFirstItem;
+  while (tok) {
+    Token* temp = tok->mNext;
+    delete tok;
+    tok = temp;
+  }
+  mCurrentItem = nullptr;
+}
+
+Token* txExprLexer::nextToken() {
+  if (!mCurrentItem) {
+    MOZ_ASSERT_UNREACHABLE("nextToken called on uninitialized lexer");
+    return nullptr;
+  }
+
+  if (mCurrentItem->mType == Token::END) {
+    // Do not progress beyond the end token
+    return mCurrentItem;
+  }
+
+  Token* token = mCurrentItem;
+  mCurrentItem = mCurrentItem->mNext;
+  return token;
+}
+
+void txExprLexer::addToken(Token* aToken) {
+  if (mLastItem) {
+    mLastItem->mNext = aToken;
+  }
+  if (!mFirstItem) {
+    mFirstItem = aToken;
+    mCurrentItem = aToken;
+  }
+  mLastItem = aToken;
+  ++mTokenCount;
+}
+
+/**
+ * Returns true if the following Token should be an operator.
+ * This is a helper for the first bullet of [XPath 3.7]
+ *  Lexical Structure
+ */
+bool txExprLexer::nextIsOperatorToken(Token* aToken) {
+  if (!aToken || aToken->mType == Token::NULL_TOKEN) {
+    return false;
+  }
+  /* This relies on the tokens having the right order in txExprLexer.h */
+  return aToken->mType < Token::COMMA || aToken->mType > Token::UNION_OP;
+}
+
+/**
+ * Parses the given string into a sequence of Tokens
+ */
+nsresult txExprLexer::parse(const nsAString& aPattern) {
+  iterator end;
+  aPattern.BeginReading(mPosition);
+  aPattern.EndReading(end);
+
+  //-- initialize previous token, this will automatically get
+  //-- deleted when it goes out of scope
+  Token nullToken(nullptr, nullptr, Token::NULL_TOKEN);
+
+  Token::Type defType;
+  Token* newToken = nullptr;
+  Token* prevToken = &nullToken;
+  bool isToken;
+
+  while (mPosition < end) {
+    defType = Token::CNAME;
+    isToken = true;
+
+    if (*mPosition == DOLLAR_SIGN) {
+      if (++mPosition == end || !XMLUtils::isLetter(*mPosition)) {
+        return NS_ERROR_XPATH_INVALID_VAR_NAME;
+      }
+      defType = Token::VAR_REFERENCE;
+    }
+    // just reuse the QName parsing, which will use defType
+    // the token to construct
+
+    if (XMLUtils::isLetter(*mPosition)) {
+      // NCName, can get QName or OperatorName;
+      //  FunctionName, NodeName, and AxisSpecifier may want whitespace,
+      //  and are dealt with below
+      iterator start = mPosition;
+      while (++mPosition < end && XMLUtils::isNCNameChar(*mPosition)) {
+        /* just go */
+      }
+      if (mPosition < end && *mPosition == COLON) {
+        // try QName or wildcard, might need to step back for axis
+        if (++mPosition == end) {
+          return NS_ERROR_XPATH_UNEXPECTED_END;
+        }
+        if (XMLUtils::isLetter(*mPosition)) {
+          while (++mPosition < end && XMLUtils::isNCNameChar(*mPosition)) {
+            /* just go */
+          }
+        } else if (*mPosition == '*' && defType != Token::VAR_REFERENCE) {
+          // eat wildcard for NameTest, bail for var ref at COLON
+          ++mPosition;
+        } else {
+          --mPosition;  // step back
+        }
+      }
+      if (nextIsOperatorToken(prevToken)) {
+        nsDependentSubstring op(Substring(start, mPosition));
+        if (nsGkAtoms::_and->Equals(op)) {
+          defType = Token::AND_OP;
+        } else if (nsGkAtoms::_or->Equals(op)) {
+          defType = Token::OR_OP;
+        } else if (nsGkAtoms::mod->Equals(op)) {
+          defType = Token::MODULUS_OP;
+        } else if (nsGkAtoms::div->Equals(op)) {
+          defType = Token::DIVIDE_OP;
+        } else {
+          // XXX QUESTION: spec is not too precise
+          // badops is sure an error, but is bad:ops, too? We say yes!
+          return NS_ERROR_XPATH_OPERATOR_EXPECTED;
+        }
+      }
+      newToken = new Token(start, mPosition, defType);
+    } else if (isXPathDigit(*mPosition)) {
+      iterator start = mPosition;
+      while (++mPosition < end && isXPathDigit(*mPosition)) {
+        /* just go */
+      }
+      if (mPosition < end && *mPosition == '.') {
+        while (++mPosition < end && isXPathDigit(*mPosition)) {
+          /* just go */
+        }
+      }
+      newToken = new Token(start, mPosition, Token::NUMBER);
+    } else {
+      switch (*mPosition) {
+          //-- ignore whitespace
+        case SPACE:
+        case TX_TAB:
+        case TX_CR:
+        case TX_LF:
+          ++mPosition;
+          isToken = false;
+          break;
+        case S_QUOTE:
+        case D_QUOTE: {
+          iterator start = mPosition;
+          while (++mPosition < end && *mPosition != *start) {
+            // eat literal
+          }
+          if (mPosition == end) {
+            mPosition = start;
+            return NS_ERROR_XPATH_UNCLOSED_LITERAL;
+          }
+          newToken = new Token(start + 1, mPosition, Token::LITERAL);
+          ++mPosition;
+        } break;
+        case PERIOD:
+          // period can be .., .(DIGITS)+ or ., check next
+          if (++mPosition == end) {
+            newToken = new Token(mPosition - 1, Token::SELF_NODE);
+          } else if (isXPathDigit(*mPosition)) {
+            iterator start = mPosition - 1;
+            while (++mPosition < end && isXPathDigit(*mPosition)) {
+              /* just go */
+            }
+            newToken = new Token(start, mPosition, Token::NUMBER);
+          } else if (*mPosition == PERIOD) {
+            ++mPosition;
+            newToken = new Token(mPosition - 2, mPosition, Token::PARENT_NODE);
+          } else {
+            newToken = new Token(mPosition - 1, Token::SELF_NODE);
+          }
+          break;
+        case COLON:  // QNames are dealt above, must be axis ident
+          if (++mPosition >= end || *mPosition != COLON ||
+              prevToken->mType != Token::CNAME) {
+            return NS_ERROR_XPATH_BAD_COLON;
+          }
+          prevToken->mType = Token::AXIS_IDENTIFIER;
+          ++mPosition;
+          isToken = false;
+          break;
+        case FORWARD_SLASH:
+          if (++mPosition < end && *mPosition == FORWARD_SLASH) {
+            ++mPosition;
+            newToken = new Token(mPosition - 2, mPosition, Token::ANCESTOR_OP);
+          } else {
+            newToken = new Token(mPosition - 1, Token::PARENT_OP);
+          }
+          break;
+        case BANG:  // can only be !=
+          if (++mPosition < end && *mPosition == EQUAL) {
+            ++mPosition;
+            newToken = new Token(mPosition - 2, mPosition, Token::NOT_EQUAL_OP);
+            break;
+          }
+          // Error ! is not not()
+          return NS_ERROR_XPATH_BAD_BANG;
+        case EQUAL:
+          newToken = new Token(mPosition, Token::EQUAL_OP);
+          ++mPosition;
+          break;
+        case L_ANGLE:
+          if (++mPosition == end) {
+            return NS_ERROR_XPATH_UNEXPECTED_END;
+          }
+          if (*mPosition == EQUAL) {
+            ++mPosition;
+            newToken =
+                new Token(mPosition - 2, mPosition, Token::LESS_OR_EQUAL_OP);
+          } else {
+            newToken = new Token(mPosition - 1, Token::LESS_THAN_OP);
+          }
+          break;
+        case R_ANGLE:
+          if (++mPosition == end) {
+            return NS_ERROR_XPATH_UNEXPECTED_END;
+          }
+          if (*mPosition == EQUAL) {
+            ++mPosition;
+            newToken =
+                new Token(mPosition - 2, mPosition, Token::GREATER_OR_EQUAL_OP);
+          } else {
+            newToken = new Token(mPosition - 1, Token::GREATER_THAN_OP);
+          }
+          break;
+        case HYPHEN:
+          newToken = new Token(mPosition, Token::SUBTRACTION_OP);
+          ++mPosition;
+          break;
+        case ASTERISK:
+          if (nextIsOperatorToken(prevToken)) {
+            newToken = new Token(mPosition, Token::MULTIPLY_OP);
+          } else {
+            newToken = new Token(mPosition, Token::CNAME);
+          }
+          ++mPosition;
+          break;
+        case L_PAREN:
+          if (prevToken->mType == Token::CNAME) {
+            const nsDependentSubstring& val = prevToken->Value();
+            if (val.EqualsLiteral("comment")) {
+              prevToken->mType = Token::COMMENT_AND_PAREN;
+            } else if (val.EqualsLiteral("node")) {
+              prevToken->mType = Token::NODE_AND_PAREN;
+            } else if (val.EqualsLiteral("processing-instruction")) {
+              prevToken->mType = Token::PROC_INST_AND_PAREN;
+            } else if (val.EqualsLiteral("text")) {
+              prevToken->mType = Token::TEXT_AND_PAREN;
+            } else {
+              prevToken->mType = Token::FUNCTION_NAME_AND_PAREN;
+            }
+            isToken = false;
+          } else {
+            newToken = new Token(mPosition, Token::L_PAREN);
+          }
+          ++mPosition;
+          break;
+        case R_PAREN:
+          newToken = new Token(mPosition, Token::R_PAREN);
+          ++mPosition;
+          break;
+        case L_BRACKET:
+          newToken = new Token(mPosition, Token::L_BRACKET);
+          ++mPosition;
+          break;
+        case R_BRACKET:
+          newToken = new Token(mPosition, Token::R_BRACKET);
+          ++mPosition;
+          break;
+        case COMMA:
+          newToken = new Token(mPosition, Token::COMMA);
+          ++mPosition;
+          break;
+        case AT_SIGN:
+          newToken = new Token(mPosition, Token::AT_SIGN);
+          ++mPosition;
+          break;
+        case PLUS:
+          newToken = new Token(mPosition, Token::ADDITION_OP);
+          ++mPosition;
+          break;
+        case VERT_BAR:
+          newToken = new Token(mPosition, Token::UNION_OP);
+          ++mPosition;
+          break;
+        default:
+          // Error, don't grok character :-(
+          return NS_ERROR_XPATH_ILLEGAL_CHAR;
+      }
+    }
+    if (isToken) {
+      NS_ENSURE_TRUE(newToken != mLastItem, NS_ERROR_FAILURE);
+      prevToken = newToken;
+      addToken(newToken);
+    }
+  }
+
+  // add a endToken to the list
+  newToken = new Token(end, end, Token::END);
+  addToken(newToken);
+
+  return NS_OK;
+}
diff --git a/dom/xslt/xpath/txExprLexer.h b/dom/xslt/xpath/txExprLexer.h
new file mode 100644
index 0000000000..9d3ca2810e
--- /dev/null
+++ b/dom/xslt/xpath/txExprLexer.h
@@ -0,0 +1,200 @@
+/* -*- Mode: C++; tab-width: 4; 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 MITREXSL_EXPRLEXER_H
+#define MITREXSL_EXPRLEXER_H
+
+#include "txCore.h"
+#include "nsString.h"
+
+/**
+ * A Token class for the ExprLexer.
+ *
+ * This class was ported from XSL:P, an open source Java based
+ * XSLT processor, written by yours truly.
+ */
+class Token {
+ public:
+  /**
+   * Token types
+   */
+  enum Type {
+    //-- Trivial Tokens
+    NULL_TOKEN = 1,
+    LITERAL,
+    NUMBER,
+    CNAME,
+    VAR_REFERENCE,
+    PARENT_NODE,
+    SELF_NODE,
+    R_PAREN,
+    R_BRACKET,  // 9
+    /**
+     * start of tokens for 3.7, bullet 1
+     * ExprLexer::nextIsOperatorToken bails if the tokens aren't
+     * consecutive.
+     */
+    COMMA,
+    AT_SIGN,
+    L_PAREN,
+    L_BRACKET,
+    AXIS_IDENTIFIER,
+
+    // These tokens include their following left parenthesis
+    FUNCTION_NAME_AND_PAREN,  // 15
+    COMMENT_AND_PAREN,
+    NODE_AND_PAREN,
+    PROC_INST_AND_PAREN,
+    TEXT_AND_PAREN,
+
+    /**
+     * operators
+     */
+    //-- boolean ops
+    AND_OP,  // 20
+    OR_OP,
+
+    //-- relational
+    EQUAL_OP,  // 22
+    NOT_EQUAL_OP,
+    LESS_THAN_OP,
+    GREATER_THAN_OP,
+    LESS_OR_EQUAL_OP,
+    GREATER_OR_EQUAL_OP,
+    //-- additive operators
+    ADDITION_OP,  // 28
+    SUBTRACTION_OP,
+    //-- multiplicative
+    DIVIDE_OP,  // 30
+    MULTIPLY_OP,
+    MODULUS_OP,
+    //-- path operators
+    PARENT_OP,  // 33
+    ANCESTOR_OP,
+    UNION_OP,
+    /**
+     * end of tokens for 3.7, bullet 1 -/
+     */
+    //-- Special endtoken
+    END  // 36
+  };
+
+  /**
+   * Constructors
+   */
+  using iterator = nsAString::const_char_iterator;
+
+  Token(iterator aStart, iterator aEnd, Type aType)
+      : mStart(aStart), mEnd(aEnd), mType(aType), mNext(nullptr) {}
+  Token(iterator aChar, Type aType)
+      : mStart(aChar), mEnd(aChar + 1), mType(aType), mNext(nullptr) {}
+
+  const nsDependentSubstring Value() { return Substring(mStart, mEnd); }
+
+  iterator mStart, mEnd;
+  Type mType;
+  Token* mNext;
+};
+
+/**
+ * A class for splitting an "Expr" String into tokens and
+ * performing  basic Lexical Analysis.
+ *
+ * This class was ported from XSL:P, an open source Java based XSL processor
+ */
+
+class txExprLexer {
+ public:
+  txExprLexer();
+  ~txExprLexer();
+
+  /**
+   * Parse the given string.
+   * returns an error result if lexing failed.
+   * The given string must outlive the use of the lexer, as the
+   * generated Tokens point to Substrings of it.
+   * mPosition points to the offending location in case of an error.
+   */
+  nsresult parse(const nsAString& aPattern);
+
+  using iterator = nsAString::const_char_iterator;
+  iterator mPosition;
+
+  /**
+   * Functions for iterating over the TokenList
+   */
+
+  Token* nextToken();
+  Token* peek() {
+    NS_ASSERTION(mCurrentItem, "peek called uninitialized lexer");
+    return mCurrentItem;
+  }
+  Token* peekAhead() {
+    NS_ASSERTION(mCurrentItem, "peekAhead called on uninitialized lexer");
+    // Don't peek past the end node
+    return (mCurrentItem && mCurrentItem->mNext) ? mCurrentItem->mNext
+                                                 : mCurrentItem;
+  }
+  bool hasMoreTokens() {
+    NS_ASSERTION(mCurrentItem, "HasMoreTokens called on uninitialized lexer");
+    return (mCurrentItem && mCurrentItem->mType != Token::END);
+  }
+
+  /**
+   * Trivial Tokens
+   */
+  //-- LF, changed to enum
+  enum _TrivialTokens {
+    D_QUOTE = '\"',
+    S_QUOTE = '\'',
+    L_PAREN = '(',
+    R_PAREN = ')',
+    L_BRACKET = '[',
+    R_BRACKET = ']',
+    L_ANGLE = '<',
+    R_ANGLE = '>',
+    COMMA = ',',
+    PERIOD = '.',
+    ASTERISK = '*',
+    FORWARD_SLASH = '/',
+    EQUAL = '=',
+    BANG = '!',
+    VERT_BAR = '|',
+    AT_SIGN = '@',
+    DOLLAR_SIGN = '$',
+    PLUS = '+',
+    HYPHEN = '-',
+    COLON = ':',
+    //-- whitespace tokens
+    SPACE = ' ',
+    TX_TAB = '\t',
+    TX_CR = '\n',
+    TX_LF = '\r'
+  };
+
+ private:
+  Token* mCurrentItem;
+  Token* mFirstItem;
+  Token* mLastItem;
+
+  int mTokenCount;
+
+  void addToken(Token* aToken);
+
+  /**
+   * Returns true if the following Token should be an operator.
+   * This is a helper for the first bullet of [XPath 3.7]
+   *  Lexical Structure
+   */
+  bool nextIsOperatorToken(Token* aToken);
+
+  /**
+   * Returns true if the given character represents a numeric letter (digit)
+   * Implemented in ExprLexerChars.cpp
+   */
+  static bool isXPathDigit(char16_t ch) { return (ch >= '0' && ch <= '9'); }
+};
+
+#endif
diff --git a/dom/xslt/xpath/txExprParser.cpp b/dom/xslt/xpath/txExprParser.cpp
new file mode 100644
index 0000000000..47f142d023
--- /dev/null
+++ b/dom/xslt/xpath/txExprParser.cpp
@@ -0,0 +1,855 @@
+/* -*- Mode: C++; tab-width: 4; 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/. */
+
+/**
+ * ExprParser
+ * This class is used to parse XSL Expressions
+ * @see ExprLexer
+ **/
+
+#include "txExprParser.h"
+
+#include <utility>
+
+#include "mozilla/UniquePtrExtensions.h"
+#include "nsError.h"
+#include "nsGkAtoms.h"
+#include "txExpr.h"
+#include "txExprLexer.h"
+#include "txIXPathContext.h"
+#include "txStack.h"
+#include "txStringUtils.h"
+#include "txXPathNode.h"
+#include "txXPathOptimizer.h"
+
+using mozilla::MakeUnique;
+using mozilla::UniquePtr;
+using mozilla::Unused;
+using mozilla::WrapUnique;
+
+/**
+ * Creates an Attribute Value Template using the given value
+ * This should move to XSLProcessor class
+ */
+nsresult txExprParser::createAVT(const nsAString& aAttrValue,
+                                 txIParseContext* aContext, Expr** aResult) {
+  *aResult = nullptr;
+  nsresult rv = NS_OK;
+  UniquePtr<Expr> expr;
+  FunctionCall* concat = nullptr;
+
+  nsAutoString literalString;
+  bool inExpr = false;
+  nsAString::const_char_iterator iter, start, end, avtStart;
+  aAttrValue.BeginReading(iter);
+  aAttrValue.EndReading(end);
+  avtStart = iter;
+
+  while (iter != end) {
+    // Every iteration through this loop parses either a literal section
+    // or an expression
+    start = iter;
+    UniquePtr<Expr> newExpr;
+    if (!inExpr) {
+      // Parse literal section
+      literalString.Truncate();
+      while (iter != end) {
+        char16_t q = *iter;
+        if (q == '{' || q == '}') {
+          // Store what we've found so far and set a new |start| to
+          // skip the (first) brace
+          literalString.Append(Substring(start, iter));
+          start = ++iter;
+          // Unless another brace follows we've found the start of
+          // an expression (in case of '{') or an unbalanced brace
+          // (in case of '}')
+          if (iter == end || *iter != q) {
+            if (q == '}') {
+              aContext->SetErrorOffset(iter - avtStart);
+              return NS_ERROR_XPATH_UNBALANCED_CURLY_BRACE;
+            }
+
+            inExpr = true;
+            break;
+          }
+          // We found a second brace, let that be part of the next
+          // literal section being parsed and continue looping
+        }
+        ++iter;
+      }
+
+      if (start == iter && literalString.IsEmpty()) {
+        // Restart the loop since we didn't create an expression
+        continue;
+      }
+      newExpr =
+          MakeUnique<txLiteralExpr>(literalString + Substring(start, iter));
+    } else {
+      // Parse expressions, iter is already past the initial '{' when
+      // we get here.
+      while (iter != end) {
+        if (*iter == '}') {
+          rv = createExprInternal(Substring(start, iter), start - avtStart,
+                                  aContext, getter_Transfers(newExpr));
+          NS_ENSURE_SUCCESS(rv, rv);
+
+          inExpr = false;
+          ++iter;  // skip closing '}'
+          break;
+        } else if (*iter == '\'' || *iter == '"') {
+          char16_t q = *iter;
+          while (++iter != end && *iter != q) {
+          } /* do nothing */
+          if (iter == end) {
+            break;
+          }
+        }
+        ++iter;
+      }
+
+      if (inExpr) {
+        aContext->SetErrorOffset(start - avtStart);
+        return NS_ERROR_XPATH_UNBALANCED_CURLY_BRACE;
+      }
+    }
+
+    // Add expression, create a concat() call if necessary
+    if (!expr) {
+      expr = std::move(newExpr);
+    } else {
+      if (!concat) {
+        concat = new txCoreFunctionCall(txCoreFunctionCall::CONCAT);
+        concat->addParam(expr.release());
+        expr = WrapUnique(concat);
+      }
+
+      concat->addParam(newExpr.release());
+    }
+  }
+
+  if (inExpr) {
+    aContext->SetErrorOffset(iter - avtStart);
+    return NS_ERROR_XPATH_UNBALANCED_CURLY_BRACE;
+  }
+
+  if (!expr) {
+    expr = MakeUnique<txLiteralExpr>(u""_ns);
+  }
+
+  *aResult = expr.release();
+
+  return NS_OK;
+}
+
+nsresult txExprParser::createExprInternal(const nsAString& aExpression,
+                                          uint32_t aSubStringPos,
+                                          txIParseContext* aContext,
+                                          Expr** aExpr) {
+  NS_ENSURE_ARG_POINTER(aExpr);
+  *aExpr = nullptr;
+  txExprLexer lexer;
+  nsresult rv = lexer.parse(aExpression);
+  if (NS_FAILED(rv)) {
+    nsAString::const_char_iterator start;
+    aExpression.BeginReading(start);
+    aContext->SetErrorOffset(lexer.mPosition - start + aSubStringPos);
+    return rv;
+  }
+  UniquePtr<Expr> expr;
+  rv = createExpr(lexer, aContext, getter_Transfers(expr));
+  if (NS_SUCCEEDED(rv) && lexer.peek()->mType != Token::END) {
+    rv = NS_ERROR_XPATH_BINARY_EXPECTED;
+  }
+  if (NS_FAILED(rv)) {
+    nsAString::const_char_iterator start;
+    aExpression.BeginReading(start);
+    aContext->SetErrorOffset(lexer.peek()->mStart - start + aSubStringPos);
+
+    return rv;
+  }
+
+  txXPathOptimizer optimizer;
+  Expr* newExpr = nullptr;
+  optimizer.optimize(expr.get(), &newExpr);
+
+  *aExpr = newExpr ? newExpr : expr.release();
+
+  return NS_OK;
+}
+
+/**
+ * Private Methods
+ */
+
+/**
+ * Creates a binary Expr for the given operator
+ */
+nsresult txExprParser::createBinaryExpr(UniquePtr<Expr>& left,
+                                        UniquePtr<Expr>& right, Token* op,
+                                        Expr** aResult) {
+  NS_ASSERTION(op, "internal error");
+  *aResult = nullptr;
+
+  Expr* expr = nullptr;
+  switch (op->mType) {
+    //-- math ops
+    case Token::ADDITION_OP:
+      expr = new txNumberExpr(left.get(), right.get(), txNumberExpr::ADD);
+      break;
+    case Token::SUBTRACTION_OP:
+      expr = new txNumberExpr(left.get(), right.get(), txNumberExpr::SUBTRACT);
+      break;
+    case Token::DIVIDE_OP:
+      expr = new txNumberExpr(left.get(), right.get(), txNumberExpr::DIVIDE);
+      break;
+    case Token::MODULUS_OP:
+      expr = new txNumberExpr(left.get(), right.get(), txNumberExpr::MODULUS);
+      break;
+    case Token::MULTIPLY_OP:
+      expr = new txNumberExpr(left.get(), right.get(), txNumberExpr::MULTIPLY);
+      break;
+
+    //-- case boolean ops
+    case Token::AND_OP:
+      expr = new BooleanExpr(left.get(), right.get(), BooleanExpr::AND);
+      break;
+    case Token::OR_OP:
+      expr = new BooleanExpr(left.get(), right.get(), BooleanExpr::OR);
+      break;
+
+    //-- equality ops
+    case Token::EQUAL_OP:
+      expr = new RelationalExpr(left.get(), right.get(), RelationalExpr::EQUAL);
+      break;
+    case Token::NOT_EQUAL_OP:
+      expr = new RelationalExpr(left.get(), right.get(),
+                                RelationalExpr::NOT_EQUAL);
+      break;
+
+    //-- relational ops
+    case Token::LESS_THAN_OP:
+      expr = new RelationalExpr(left.get(), right.get(),
+                                RelationalExpr::LESS_THAN);
+      break;
+    case Token::GREATER_THAN_OP:
+      expr = new RelationalExpr(left.get(), right.get(),
+                                RelationalExpr::GREATER_THAN);
+      break;
+    case Token::LESS_OR_EQUAL_OP:
+      expr = new RelationalExpr(left.get(), right.get(),
+                                RelationalExpr::LESS_OR_EQUAL);
+      break;
+    case Token::GREATER_OR_EQUAL_OP:
+      expr = new RelationalExpr(left.get(), right.get(),
+                                RelationalExpr::GREATER_OR_EQUAL);
+      break;
+
+    default:
+      MOZ_ASSERT_UNREACHABLE("operator tokens should be already checked");
+      return NS_ERROR_UNEXPECTED;
+  }
+
+  Unused << left.release();
+  Unused << right.release();
+
+  *aResult = expr;
+  return NS_OK;
+}
+
+nsresult txExprParser::createExpr(txExprLexer& lexer, txIParseContext* aContext,
+                                  Expr** aResult) {
+  *aResult = nullptr;
+
+  nsresult rv = NS_OK;
+  bool done = false;
+
+  UniquePtr<Expr> expr;
+
+  txStack exprs;
+  txStack ops;
+
+  while (!done) {
+    uint16_t negations = 0;
+    while (lexer.peek()->mType == Token::SUBTRACTION_OP) {
+      negations++;
+      lexer.nextToken();
+    }
+
+    rv = createUnionExpr(lexer, aContext, getter_Transfers(expr));
+    if (NS_FAILED(rv)) {
+      break;
+    }
+
+    if (negations > 0) {
+      if (negations % 2 == 0) {
+        auto fcExpr =
+            MakeUnique<txCoreFunctionCall>(txCoreFunctionCall::NUMBER);
+
+        fcExpr->addParam(expr.release());
+        expr = std::move(fcExpr);
+      } else {
+        expr = MakeUnique<UnaryExpr>(expr.release());
+      }
+    }
+
+    short tokPrecedence = precedence(lexer.peek());
+    if (tokPrecedence != 0) {
+      Token* tok = lexer.nextToken();
+      while (!exprs.isEmpty() &&
+             tokPrecedence <= precedence(static_cast<Token*>(ops.peek()))) {
+        // can't use expr as argument due to order of evaluation
+        UniquePtr<Expr> left(static_cast<Expr*>(exprs.pop()));
+        UniquePtr<Expr> right(std::move(expr));
+        rv = createBinaryExpr(left, right, static_cast<Token*>(ops.pop()),
+                              getter_Transfers(expr));
+        if (NS_FAILED(rv)) {
+          done = true;
+          break;
+        }
+      }
+      exprs.push(expr.release());
+      ops.push(tok);
+    } else {
+      done = true;
+    }
+  }
+
+  while (NS_SUCCEEDED(rv) && !exprs.isEmpty()) {
+    UniquePtr<Expr> left(static_cast<Expr*>(exprs.pop()));
+    UniquePtr<Expr> right(std::move(expr));
+    rv = createBinaryExpr(left, right, static_cast<Token*>(ops.pop()),
+                          getter_Transfers(expr));
+  }
+  // clean up on error
+  while (!exprs.isEmpty()) {
+    delete static_cast<Expr*>(exprs.pop());
+  }
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  *aResult = expr.release();
+  return NS_OK;
+}
+
+nsresult txExprParser::createFilterOrStep(txExprLexer& lexer,
+                                          txIParseContext* aContext,
+                                          Expr** aResult) {
+  *aResult = nullptr;
+
+  nsresult rv = NS_OK;
+  Token* tok = lexer.peek();
+
+  UniquePtr<Expr> expr;
+  switch (tok->mType) {
+    case Token::FUNCTION_NAME_AND_PAREN:
+      rv = createFunctionCall(lexer, aContext, getter_Transfers(expr));
+      NS_ENSURE_SUCCESS(rv, rv);
+      break;
+    case Token::VAR_REFERENCE:
+      lexer.nextToken();
+      {
+        RefPtr<nsAtom> prefix, lName;
+        int32_t nspace;
+        nsresult rv = resolveQName(tok->Value(), getter_AddRefs(prefix),
+                                   aContext, getter_AddRefs(lName), nspace);
+        NS_ENSURE_SUCCESS(rv, rv);
+        expr = MakeUnique<VariableRefExpr>(prefix, lName, nspace);
+      }
+      break;
+    case Token::L_PAREN:
+      lexer.nextToken();
+      rv = createExpr(lexer, aContext, getter_Transfers(expr));
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      if (lexer.peek()->mType != Token::R_PAREN) {
+        return NS_ERROR_XPATH_PAREN_EXPECTED;
+      }
+      lexer.nextToken();
+      break;
+    case Token::LITERAL:
+      lexer.nextToken();
+      expr = MakeUnique<txLiteralExpr>(tok->Value());
+      break;
+    case Token::NUMBER: {
+      lexer.nextToken();
+      expr = MakeUnique<txLiteralExpr>(txDouble::toDouble(tok->Value()));
+      break;
+    }
+    default:
+      return createLocationStep(lexer, aContext, aResult);
+  }
+
+  if (lexer.peek()->mType == Token::L_BRACKET) {
+    UniquePtr<FilterExpr> filterExpr(new FilterExpr(expr.get()));
+
+    Unused << expr.release();
+
+    //-- handle predicates
+    rv = parsePredicates(filterExpr.get(), lexer, aContext);
+    NS_ENSURE_SUCCESS(rv, rv);
+    expr = std::move(filterExpr);
+  }
+
+  *aResult = expr.release();
+  return NS_OK;
+}
+
+nsresult txExprParser::createFunctionCall(txExprLexer& lexer,
+                                          txIParseContext* aContext,
+                                          Expr** aResult) {
+  *aResult = nullptr;
+
+  UniquePtr<FunctionCall> fnCall;
+
+  Token* tok = lexer.nextToken();
+  NS_ASSERTION(tok->mType == Token::FUNCTION_NAME_AND_PAREN,
+               "FunctionCall expected");
+
+  //-- compare function names
+  RefPtr<nsAtom> prefix, lName;
+  int32_t namespaceID;
+  nsresult rv = resolveQName(tok->Value(), getter_AddRefs(prefix), aContext,
+                             getter_AddRefs(lName), namespaceID);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  txCoreFunctionCall::eType type;
+  if (namespaceID == kNameSpaceID_None &&
+      txCoreFunctionCall::getTypeFromAtom(lName, type)) {
+    // It is a known built-in function.
+    fnCall = MakeUnique<txCoreFunctionCall>(type);
+  }
+
+  // check extension functions and xslt
+  if (!fnCall) {
+    rv = aContext->resolveFunctionCall(lName, namespaceID,
+                                       getter_Transfers(fnCall));
+
+    if (rv == NS_ERROR_NOT_IMPLEMENTED) {
+      // this should just happen for unparsed-entity-uri()
+      NS_ASSERTION(!fnCall, "Now is it implemented or not?");
+      rv = parseParameters(0, lexer, aContext);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      *aResult = new txLiteralExpr(tok->Value() + u" not implemented."_ns);
+
+      return NS_OK;
+    }
+
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
+  //-- handle parametes
+  rv = parseParameters(fnCall.get(), lexer, aContext);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  *aResult = fnCall.release();
+  return NS_OK;
+}
+
+nsresult txExprParser::createLocationStep(txExprLexer& lexer,
+                                          txIParseContext* aContext,
+                                          Expr** aExpr) {
+  *aExpr = nullptr;
+
+  //-- child axis is default
+  LocationStep::LocationStepType axisIdentifier = LocationStep::CHILD_AXIS;
+  UniquePtr<txNodeTest> nodeTest;
+
+  //-- get Axis Identifier or AbbreviatedStep, if present
+  Token* tok = lexer.peek();
+  switch (tok->mType) {
+    case Token::AXIS_IDENTIFIER: {
+      //-- eat token
+      lexer.nextToken();
+      RefPtr<nsAtom> axis = NS_Atomize(tok->Value());
+      if (axis == nsGkAtoms::ancestor) {
+        axisIdentifier = LocationStep::ANCESTOR_AXIS;
+      } else if (axis == nsGkAtoms::ancestorOrSelf) {
+        axisIdentifier = LocationStep::ANCESTOR_OR_SELF_AXIS;
+      } else if (axis == nsGkAtoms::attribute) {
+        axisIdentifier = LocationStep::ATTRIBUTE_AXIS;
+      } else if (axis == nsGkAtoms::child) {
+        axisIdentifier = LocationStep::CHILD_AXIS;
+      } else if (axis == nsGkAtoms::descendant) {
+        axisIdentifier = LocationStep::DESCENDANT_AXIS;
+      } else if (axis == nsGkAtoms::descendantOrSelf) {
+        axisIdentifier = LocationStep::DESCENDANT_OR_SELF_AXIS;
+      } else if (axis == nsGkAtoms::following) {
+        axisIdentifier = LocationStep::FOLLOWING_AXIS;
+      } else if (axis == nsGkAtoms::followingSibling) {
+        axisIdentifier = LocationStep::FOLLOWING_SIBLING_AXIS;
+      } else if (axis == nsGkAtoms::_namespace) {
+        axisIdentifier = LocationStep::NAMESPACE_AXIS;
+      } else if (axis == nsGkAtoms::parent) {
+        axisIdentifier = LocationStep::PARENT_AXIS;
+      } else if (axis == nsGkAtoms::preceding) {
+        axisIdentifier = LocationStep::PRECEDING_AXIS;
+      } else if (axis == nsGkAtoms::precedingSibling) {
+        axisIdentifier = LocationStep::PRECEDING_SIBLING_AXIS;
+      } else if (axis == nsGkAtoms::self) {
+        axisIdentifier = LocationStep::SELF_AXIS;
+      } else {
+        return NS_ERROR_XPATH_INVALID_AXIS;
+      }
+      break;
+    }
+    case Token::AT_SIGN:
+      //-- eat token
+      lexer.nextToken();
+      axisIdentifier = LocationStep::ATTRIBUTE_AXIS;
+      break;
+    case Token::PARENT_NODE:
+      //-- eat token
+      lexer.nextToken();
+      axisIdentifier = LocationStep::PARENT_AXIS;
+      nodeTest = MakeUnique<txNodeTypeTest>(txNodeTypeTest::NODE_TYPE);
+      break;
+    case Token::SELF_NODE:
+      //-- eat token
+      lexer.nextToken();
+      axisIdentifier = LocationStep::SELF_AXIS;
+      nodeTest = MakeUnique<txNodeTypeTest>(txNodeTypeTest::NODE_TYPE);
+      break;
+    default:
+      break;
+  }
+
+  //-- get NodeTest unless an AbbreviatedStep was found
+  nsresult rv = NS_OK;
+  if (!nodeTest) {
+    tok = lexer.peek();
+
+    if (tok->mType == Token::CNAME) {
+      lexer.nextToken();
+      // resolve QName
+      RefPtr<nsAtom> prefix, lName;
+      int32_t nspace;
+      rv = resolveQName(tok->Value(), getter_AddRefs(prefix), aContext,
+                        getter_AddRefs(lName), nspace, true);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      nodeTest = MakeUnique<txNameTest>(
+          prefix, lName, nspace,
+          axisIdentifier == LocationStep::ATTRIBUTE_AXIS
+              ? static_cast<uint16_t>(txXPathNodeType::ATTRIBUTE_NODE)
+              : static_cast<uint16_t>(txXPathNodeType::ELEMENT_NODE));
+    } else {
+      rv = createNodeTypeTest(lexer, getter_Transfers(nodeTest));
+      NS_ENSURE_SUCCESS(rv, rv);
+    }
+  }
+
+  UniquePtr<LocationStep> lstep(
+      new LocationStep(nodeTest.get(), axisIdentifier));
+
+  Unused << nodeTest.release();
+
+  //-- handle predicates
+  rv = parsePredicates(lstep.get(), lexer, aContext);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  *aExpr = lstep.release();
+  return NS_OK;
+}
+
+/**
+ * This method only handles comment(), text(), processing-instructing()
+ * and node()
+ */
+nsresult txExprParser::createNodeTypeTest(txExprLexer& lexer,
+                                          txNodeTest** aTest) {
+  *aTest = 0;
+  UniquePtr<txNodeTypeTest> nodeTest;
+
+  Token* nodeTok = lexer.peek();
+
+  switch (nodeTok->mType) {
+    case Token::COMMENT_AND_PAREN:
+      lexer.nextToken();
+      nodeTest = MakeUnique<txNodeTypeTest>(txNodeTypeTest::COMMENT_TYPE);
+      break;
+    case Token::NODE_AND_PAREN:
+      lexer.nextToken();
+      nodeTest = MakeUnique<txNodeTypeTest>(txNodeTypeTest::NODE_TYPE);
+      break;
+    case Token::PROC_INST_AND_PAREN:
+      lexer.nextToken();
+      nodeTest = MakeUnique<txNodeTypeTest>(txNodeTypeTest::PI_TYPE);
+      break;
+    case Token::TEXT_AND_PAREN:
+      lexer.nextToken();
+      nodeTest = MakeUnique<txNodeTypeTest>(txNodeTypeTest::TEXT_TYPE);
+      break;
+    default:
+      return NS_ERROR_XPATH_NO_NODE_TYPE_TEST;
+  }
+
+  if (nodeTok->mType == Token::PROC_INST_AND_PAREN &&
+      lexer.peek()->mType == Token::LITERAL) {
+    Token* tok = lexer.nextToken();
+    nodeTest->setNodeName(tok->Value());
+  }
+  if (lexer.peek()->mType != Token::R_PAREN) {
+    return NS_ERROR_XPATH_PAREN_EXPECTED;
+  }
+  lexer.nextToken();
+
+  *aTest = nodeTest.release();
+  return NS_OK;
+}
+
+/**
+ * Creates a PathExpr using the given txExprLexer
+ * @param lexer the txExprLexer for retrieving Tokens
+ */
+nsresult txExprParser::createPathExpr(txExprLexer& lexer,
+                                      txIParseContext* aContext,
+                                      Expr** aResult) {
+  *aResult = nullptr;
+
+  UniquePtr<Expr> expr;
+
+  Token* tok = lexer.peek();
+
+  // is this a root expression?
+  if (tok->mType == Token::PARENT_OP) {
+    if (!isLocationStepToken(lexer.peekAhead())) {
+      lexer.nextToken();
+      *aResult = new RootExpr();
+      return NS_OK;
+    }
+  }
+
+  // parse first step (possibly a FilterExpr)
+  nsresult rv = NS_OK;
+  if (tok->mType != Token::PARENT_OP && tok->mType != Token::ANCESTOR_OP) {
+    rv = createFilterOrStep(lexer, aContext, getter_Transfers(expr));
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    // is this a singlestep path expression?
+    tok = lexer.peek();
+    if (tok->mType != Token::PARENT_OP && tok->mType != Token::ANCESTOR_OP) {
+      *aResult = expr.release();
+      return NS_OK;
+    }
+  } else {
+    expr = MakeUnique<RootExpr>();
+
+#ifdef TX_TO_STRING
+    static_cast<RootExpr*>(expr.get())->setSerialize(false);
+#endif
+  }
+
+  // We have a PathExpr containing several steps
+  UniquePtr<PathExpr> pathExpr(new PathExpr());
+  pathExpr->addExpr(expr.release(), PathExpr::RELATIVE_OP);
+
+  // this is ugly
+  while (1) {
+    PathExpr::PathOperator pathOp;
+    switch (lexer.peek()->mType) {
+      case Token::ANCESTOR_OP:
+        pathOp = PathExpr::DESCENDANT_OP;
+        break;
+      case Token::PARENT_OP:
+        pathOp = PathExpr::RELATIVE_OP;
+        break;
+      default:
+        *aResult = pathExpr.release();
+        return NS_OK;
+    }
+    lexer.nextToken();
+
+    rv = createLocationStep(lexer, aContext, getter_Transfers(expr));
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    pathExpr->addExpr(expr.release(), pathOp);
+  }
+  MOZ_ASSERT_UNREACHABLE("internal xpath parser error");
+  return NS_ERROR_UNEXPECTED;
+}
+
+/**
+ * Creates a PathExpr using the given txExprLexer
+ * @param lexer the txExprLexer for retrieving Tokens
+ */
+nsresult txExprParser::createUnionExpr(txExprLexer& lexer,
+                                       txIParseContext* aContext,
+                                       Expr** aResult) {
+  *aResult = nullptr;
+
+  UniquePtr<Expr> expr;
+  nsresult rv = createPathExpr(lexer, aContext, getter_Transfers(expr));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  if (lexer.peek()->mType != Token::UNION_OP) {
+    *aResult = expr.release();
+    return NS_OK;
+  }
+
+  UniquePtr<UnionExpr> unionExpr(new UnionExpr());
+  unionExpr->addExpr(expr.release());
+
+  while (lexer.peek()->mType == Token::UNION_OP) {
+    lexer.nextToken();  //-- eat token
+
+    rv = createPathExpr(lexer, aContext, getter_Transfers(expr));
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    unionExpr->addExpr(expr.release());
+  }
+
+  *aResult = unionExpr.release();
+  return NS_OK;
+}
+
+bool txExprParser::isLocationStepToken(Token* aToken) {
+  // We could put these in consecutive order in ExprLexer.h for speed
+  return aToken->mType == Token::AXIS_IDENTIFIER ||
+         aToken->mType == Token::AT_SIGN ||
+         aToken->mType == Token::PARENT_NODE ||
+         aToken->mType == Token::SELF_NODE || aToken->mType == Token::CNAME ||
+         aToken->mType == Token::COMMENT_AND_PAREN ||
+         aToken->mType == Token::NODE_AND_PAREN ||
+         aToken->mType == Token::PROC_INST_AND_PAREN ||
+         aToken->mType == Token::TEXT_AND_PAREN;
+}
+
+/**
+ * Using the given lexer, parses the tokens if they represent a predicate list
+ * If an error occurs a non-zero String pointer will be returned containing the
+ * error message.
+ * @param predicateList, the PredicateList to add predicate expressions to
+ * @param lexer the txExprLexer to use for parsing tokens
+ * @return 0 if successful, or a String pointer to the error message
+ */
+nsresult txExprParser::parsePredicates(PredicateList* aPredicateList,
+                                       txExprLexer& lexer,
+                                       txIParseContext* aContext) {
+  UniquePtr<Expr> expr;
+  nsresult rv = NS_OK;
+  while (lexer.peek()->mType == Token::L_BRACKET) {
+    //-- eat Token
+    lexer.nextToken();
+
+    rv = createExpr(lexer, aContext, getter_Transfers(expr));
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    aPredicateList->add(expr.release());
+
+    if (lexer.peek()->mType != Token::R_BRACKET) {
+      return NS_ERROR_XPATH_BRACKET_EXPECTED;
+    }
+    lexer.nextToken();
+  }
+  return NS_OK;
+}
+
+/**
+ * Using the given lexer, parses the tokens if they represent a parameter list
+ * If an error occurs a non-zero String pointer will be returned containing the
+ * error message.
+ * @param list, the List to add parameter expressions to
+ * @param lexer the txExprLexer to use for parsing tokens
+ * @return NS_OK if successful, or another rv otherwise
+ */
+nsresult txExprParser::parseParameters(FunctionCall* aFnCall,
+                                       txExprLexer& lexer,
+                                       txIParseContext* aContext) {
+  if (lexer.peek()->mType == Token::R_PAREN) {
+    lexer.nextToken();
+    return NS_OK;
+  }
+
+  UniquePtr<Expr> expr;
+  nsresult rv = NS_OK;
+  while (1) {
+    rv = createExpr(lexer, aContext, getter_Transfers(expr));
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    if (aFnCall) {
+      aFnCall->addParam(expr.release());
+    }
+
+    switch (lexer.peek()->mType) {
+      case Token::R_PAREN:
+        lexer.nextToken();
+        return NS_OK;
+      case Token::COMMA:  //-- param separator
+        lexer.nextToken();
+        break;
+      default:
+        return NS_ERROR_XPATH_PAREN_EXPECTED;
+    }
+  }
+
+  MOZ_ASSERT_UNREACHABLE("internal xpath parser error");
+  return NS_ERROR_UNEXPECTED;
+}
+
+short txExprParser::precedence(Token* aToken) {
+  switch (aToken->mType) {
+    case Token::OR_OP:
+      return 1;
+    case Token::AND_OP:
+      return 2;
+    //-- equality
+    case Token::EQUAL_OP:
+    case Token::NOT_EQUAL_OP:
+      return 3;
+    //-- relational
+    case Token::LESS_THAN_OP:
+    case Token::GREATER_THAN_OP:
+    case Token::LESS_OR_EQUAL_OP:
+    case Token::GREATER_OR_EQUAL_OP:
+      return 4;
+    //-- additive operators
+    case Token::ADDITION_OP:
+    case Token::SUBTRACTION_OP:
+      return 5;
+    //-- multiplicative
+    case Token::DIVIDE_OP:
+    case Token::MULTIPLY_OP:
+    case Token::MODULUS_OP:
+      return 6;
+    default:
+      break;
+  }
+  return 0;
+}
+
+nsresult txExprParser::resolveQName(const nsAString& aQName, nsAtom** aPrefix,
+                                    txIParseContext* aContext,
+                                    nsAtom** aLocalName, int32_t& aNamespace,
+                                    bool aIsNameTest) {
+  aNamespace = kNameSpaceID_None;
+  int32_t idx = aQName.FindChar(':');
+  if (idx > 0) {
+    *aPrefix = NS_Atomize(StringHead(aQName, (uint32_t)idx)).take();
+    if (!*aPrefix) {
+      return NS_ERROR_OUT_OF_MEMORY;
+    }
+    *aLocalName = NS_Atomize(Substring(aQName, (uint32_t)idx + 1,
+                                       aQName.Length() - (idx + 1)))
+                      .take();
+    if (!*aLocalName) {
+      NS_RELEASE(*aPrefix);
+      return NS_ERROR_OUT_OF_MEMORY;
+    }
+    return aContext->resolveNamespacePrefix(*aPrefix, aNamespace);
+  }
+  // the lexer dealt with idx == 0
+  *aPrefix = 0;
+  if (aIsNameTest && aContext->caseInsensitiveNameTests()) {
+    nsAutoString lcname;
+    nsContentUtils::ASCIIToLower(aQName, lcname);
+    *aLocalName = NS_Atomize(lcname).take();
+  } else {
+    *aLocalName = NS_Atomize(aQName).take();
+  }
+  if (!*aLocalName) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+  return NS_OK;
+}
diff --git a/dom/xslt/xpath/txExprParser.h b/dom/xslt/xpath/txExprParser.h
new file mode 100644
index 0000000000..06c07cf232
--- /dev/null
+++ b/dom/xslt/xpath/txExprParser.h
@@ -0,0 +1,95 @@
+/* -*- Mode: C++; tab-width: 4; 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/. */
+
+/**
+ * ExprParser
+ * This class is used to parse XSL Expressions
+ * @see ExprLexer
+ **/
+
+#ifndef MITREXSL_EXPRPARSER_H
+#define MITREXSL_EXPRPARSER_H
+
+#include "txCore.h"
+#include "mozilla/UniquePtr.h"
+#include "nsString.h"
+
+class Expr;
+class txExprLexer;
+class FunctionCall;
+class LocationStep;
+class nsAtom;
+class PredicateList;
+class Token;
+class txIParseContext;
+class txNodeTest;
+
+class txExprParser {
+ public:
+  static nsresult createExpr(const nsAString& aExpression,
+                             txIParseContext* aContext, Expr** aExpr) {
+    return createExprInternal(aExpression, 0, aContext, aExpr);
+  }
+
+  /**
+   * Creates an Attribute Value Template using the given value
+   */
+  static nsresult createAVT(const nsAString& aAttrValue,
+                            txIParseContext* aContext, Expr** aResult);
+
+ protected:
+  static nsresult createExprInternal(const nsAString& aExpression,
+                                     uint32_t aSubStringPos,
+                                     txIParseContext* aContext, Expr** aExpr);
+  /**
+   * Using nsAutoPtr& to optimize passing the ownership to the
+   * created binary expression objects.
+   */
+  static nsresult createBinaryExpr(mozilla::UniquePtr<Expr>& left,
+                                   mozilla::UniquePtr<Expr>& right, Token* op,
+                                   Expr** aResult);
+  static nsresult createExpr(txExprLexer& lexer, txIParseContext* aContext,
+                             Expr** aResult);
+  static nsresult createFilterOrStep(txExprLexer& lexer,
+                                     txIParseContext* aContext, Expr** aResult);
+  static nsresult createFunctionCall(txExprLexer& lexer,
+                                     txIParseContext* aContext, Expr** aResult);
+  static nsresult createLocationStep(txExprLexer& lexer,
+                                     txIParseContext* aContext, Expr** aResult);
+  static nsresult createNodeTypeTest(txExprLexer& lexer, txNodeTest** aResult);
+  static nsresult createPathExpr(txExprLexer& lexer, txIParseContext* aContext,
+                                 Expr** aResult);
+  static nsresult createUnionExpr(txExprLexer& lexer, txIParseContext* aContext,
+                                  Expr** aResult);
+
+  static bool isLocationStepToken(Token* aToken);
+
+  static short precedence(Token* aToken);
+
+  /**
+   * Resolve a QName, given the mContext parse context.
+   * Returns prefix and localName as well as namespace ID
+   */
+  static nsresult resolveQName(const nsAString& aQName, nsAtom** aPrefix,
+                               txIParseContext* aContext, nsAtom** aLocalName,
+                               int32_t& aNamespace, bool aIsNameTest = false);
+
+  /**
+   * Using the given lexer, parses the tokens if they represent a
+   * predicate list
+   * If an error occurs a non-zero String pointer will be returned
+   * containing the error message.
+   * @param predicateList, the PredicateList to add predicate expressions to
+   * @param lexer the ExprLexer to use for parsing tokens
+   * @return 0 if successful, or a String pointer to the error message
+   */
+  static nsresult parsePredicates(PredicateList* aPredicateList,
+                                  txExprLexer& lexer,
+                                  txIParseContext* aContext);
+  static nsresult parseParameters(FunctionCall* aFnCall, txExprLexer& lexer,
+                                  txIParseContext* aContext);
+};
+
+#endif
diff --git a/dom/xslt/xpath/txExprResult.h b/dom/xslt/xpath/txExprResult.h
new file mode 100644
index 0000000000..5572b222f5
--- /dev/null
+++ b/dom/xslt/xpath/txExprResult.h
@@ -0,0 +1,118 @@
+/* -*- Mode: C++; tab-width: 4; 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 TRANSFRMX_EXPRRESULT_H
+#define TRANSFRMX_EXPRRESULT_H
+
+#include "nsString.h"
+#include "txCore.h"
+#include "txResultRecycler.h"
+
+/*
+ * ExprResult
+ *
+ * Classes Represented:
+ * BooleanResult, ExprResult, NumberResult, StringResult
+ *
+ * Note: for NodeSet, see NodeSet.h
+ */
+
+class txAExprResult {
+ public:
+  friend class txResultRecycler;
+
+  // Update txLiteralExpr::getReturnType and sTypes in txEXSLTFunctions.cpp if
+  // this enum is changed.
+  enum ResultType {
+    NODESET = 0,
+    BOOLEAN,
+    NUMBER,
+    STRING,
+    RESULT_TREE_FRAGMENT
+  };
+
+  explicit txAExprResult(txResultRecycler* aRecycler) : mRecycler(aRecycler) {}
+  virtual ~txAExprResult() = default;
+
+  void AddRef() {
+    ++mRefCnt;
+    NS_LOG_ADDREF(this, mRefCnt, "txAExprResult", sizeof(*this));
+  }
+
+  void Release();  // Implemented in txResultRecycler.cpp
+
+  /**
+   * Returns the type of ExprResult represented
+   * @return the type of ExprResult represented
+   **/
+  virtual short getResultType() = 0;
+
+  /**
+   * Creates a String representation of this ExprResult
+   * @param aResult the destination string to append the String
+   *                representation to.
+   **/
+  virtual void stringValue(nsString& aResult) = 0;
+
+  /**
+   * Returns a pointer to the stringvalue if possible. Otherwise null is
+   * returned.
+   */
+  virtual const nsString* stringValuePointer() = 0;
+
+  /**
+   * Converts this ExprResult to a Boolean (bool) value
+   * @return the Boolean value
+   **/
+  virtual bool booleanValue() = 0;
+
+  /**
+   * Converts this ExprResult to a Number (double) value
+   * @return the Number value
+   **/
+  virtual double numberValue() = 0;
+
+ private:
+  nsAutoRefCnt mRefCnt;
+  RefPtr<txResultRecycler> mRecycler;
+};
+
+#define TX_DECL_EXPRRESULT                               \
+  virtual short getResultType() override;                \
+  virtual void stringValue(nsString& aString) override;  \
+  virtual const nsString* stringValuePointer() override; \
+  virtual bool booleanValue() override;                  \
+  virtual double numberValue() override;
+
+class BooleanResult : public txAExprResult {
+ public:
+  explicit BooleanResult(bool aValue);
+
+  TX_DECL_EXPRRESULT
+
+ private:
+  bool value;
+};
+
+class NumberResult : public txAExprResult {
+ public:
+  NumberResult(double aValue, txResultRecycler* aRecycler);
+
+  TX_DECL_EXPRRESULT
+
+  double value;
+};
+
+class StringResult : public txAExprResult {
+ public:
+  explicit StringResult(txResultRecycler* aRecycler);
+  StringResult(const nsAString& aValue, txResultRecycler* aRecycler);
+
+  TX_DECL_EXPRRESULT
+
+  nsString mValue;
+};
+
+#endif
diff --git a/dom/xslt/xpath/txFilterExpr.cpp b/dom/xslt/xpath/txFilterExpr.cpp
new file mode 100644
index 0000000000..f632683290
--- /dev/null
+++ b/dom/xslt/xpath/txFilterExpr.cpp
@@ -0,0 +1,88 @@
+/* -*- Mode: C++; tab-width: 4; 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/. */
+
+#include "txExpr.h"
+#include "txNodeSet.h"
+#include "txIXPathContext.h"
+
+using mozilla::Unused;
+using mozilla::WrapUnique;
+
+//-- Implementation of FilterExpr --/
+
+//-----------------------------/
+//- Virtual methods from Expr -/
+//-----------------------------/
+
+/**
+ * Evaluates this Expr based on the given context node and processor state
+ * @param context the context node for evaluation of this Expr
+ * @param ps the ProcessorState containing the stack information needed
+ * for evaluation
+ * @return the result of the evaluation
+ * @see Expr
+ **/
+nsresult FilterExpr::evaluate(txIEvalContext* aContext,
+                              txAExprResult** aResult) {
+  *aResult = nullptr;
+
+  RefPtr<txAExprResult> exprRes;
+  nsresult rv = expr->evaluate(aContext, getter_AddRefs(exprRes));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  NS_ENSURE_TRUE(exprRes->getResultType() == txAExprResult::NODESET,
+                 NS_ERROR_XSLT_NODESET_EXPECTED);
+
+  RefPtr<txNodeSet> nodes =
+      static_cast<txNodeSet*>(static_cast<txAExprResult*>(exprRes));
+  // null out exprRes so that we can test for shared-ness
+  exprRes = nullptr;
+
+  RefPtr<txNodeSet> nonShared;
+  rv = aContext->recycler()->getNonSharedNodeSet(nodes,
+                                                 getter_AddRefs(nonShared));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = evaluatePredicates(nonShared, aContext);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  *aResult = nonShared;
+  NS_ADDREF(*aResult);
+
+  return NS_OK;
+}  //-- evaluate
+
+TX_IMPL_EXPR_STUBS_BASE(FilterExpr, NODESET_RESULT)
+
+Expr* FilterExpr::getSubExprAt(uint32_t aPos) {
+  if (aPos == 0) {
+    return expr.get();
+  }
+  return PredicateList::getSubExprAt(aPos - 1);
+}
+
+void FilterExpr::setSubExprAt(uint32_t aPos, Expr* aExpr) {
+  if (aPos == 0) {
+    Unused << expr.release();
+    expr = WrapUnique(aExpr);
+  } else {
+    PredicateList::setSubExprAt(aPos - 1, aExpr);
+  }
+}
+
+bool FilterExpr::isSensitiveTo(ContextSensitivity aContext) {
+  return expr->isSensitiveTo(aContext) ||
+         PredicateList::isSensitiveTo(aContext);
+}
+
+#ifdef TX_TO_STRING
+void FilterExpr::toString(nsAString& str) {
+  if (expr)
+    expr->toString(str);
+  else
+    str.AppendLiteral("null");
+  PredicateList::toString(str);
+}
+#endif
diff --git a/dom/xslt/xpath/txForwardContext.cpp b/dom/xslt/xpath/txForwardContext.cpp
new file mode 100644
index 0000000000..44b53fefbc
--- /dev/null
+++ b/dom/xslt/xpath/txForwardContext.cpp
@@ -0,0 +1,50 @@
+/* -*- Mode: C++; tab-width: 4; 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/. */
+
+#include "txForwardContext.h"
+#include "txNodeSet.h"
+
+const txXPathNode& txForwardContext::getContextNode() { return mContextNode; }
+
+uint32_t txForwardContext::size() { return (uint32_t)mContextSet->size(); }
+
+uint32_t txForwardContext::position() {
+  int32_t pos = mContextSet->indexOf(mContextNode);
+  NS_ASSERTION(pos >= 0, "Context is not member of context node list.");
+  return (uint32_t)(pos + 1);
+}
+
+nsresult txForwardContext::getVariable(int32_t aNamespace, nsAtom* aLName,
+                                       txAExprResult*& aResult) {
+  NS_ASSERTION(mInner, "mInner is null!!!");
+  return mInner->getVariable(aNamespace, aLName, aResult);
+}
+
+nsresult txForwardContext::isStripSpaceAllowed(const txXPathNode& aNode,
+                                               bool& aAllowed) {
+  NS_ASSERTION(mInner, "mInner is null!!!");
+  return mInner->isStripSpaceAllowed(aNode, aAllowed);
+}
+
+void* txForwardContext::getPrivateContext() {
+  NS_ASSERTION(mInner, "mInner is null!!!");
+  return mInner->getPrivateContext();
+}
+
+txResultRecycler* txForwardContext::recycler() {
+  NS_ASSERTION(mInner, "mInner is null!!!");
+  return mInner->recycler();
+}
+
+void txForwardContext::receiveError(const nsAString& aMsg, nsresult aRes) {
+  NS_ASSERTION(mInner, "mInner is null!!!");
+#ifdef DEBUG
+  nsAutoString error(u"forwarded error: "_ns);
+  error.Append(aMsg);
+  mInner->receiveError(error, aRes);
+#else
+  mInner->receiveError(aMsg, aRes);
+#endif
+}
diff --git a/dom/xslt/xpath/txForwardContext.h b/dom/xslt/xpath/txForwardContext.h
new file mode 100644
index 0000000000..447f2fbfc1
--- /dev/null
+++ b/dom/xslt/xpath/txForwardContext.h
@@ -0,0 +1,28 @@
+/* -*- Mode: C++; tab-width: 4; 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 __TX_XPATH_CONTEXT
+#define __TX_XPATH_CONTEXT
+
+#include "txIXPathContext.h"
+#include "txNodeSet.h"
+
+class txForwardContext : public txIEvalContext {
+ public:
+  txForwardContext(txIMatchContext* aContext, const txXPathNode& aContextNode,
+                   txNodeSet* aContextNodeSet)
+      : mInner(aContext),
+        mContextNode(aContextNode),
+        mContextSet(aContextNodeSet) {}
+
+  TX_DECL_EVAL_CONTEXT;
+
+ private:
+  txIMatchContext* mInner;
+  const txXPathNode& mContextNode;
+  RefPtr<txNodeSet> mContextSet;
+};
+
+#endif  // __TX_XPATH_CONTEXT
diff --git a/dom/xslt/xpath/txFunctionCall.cpp b/dom/xslt/xpath/txFunctionCall.cpp
new file mode 100644
index 0000000000..17a325e2ad
--- /dev/null
+++ b/dom/xslt/xpath/txFunctionCall.cpp
@@ -0,0 +1,110 @@
+/* -*- Mode: C++; tab-width: 4; 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/. */
+
+#include "txExpr.h"
+#include "nsAtom.h"
+#include "txIXPathContext.h"
+#include "txNodeSet.h"
+
+#ifdef TX_TO_STRING
+#  include "nsReadableUtils.h"
+#endif
+
+/**
+ * This class represents a FunctionCall as defined by the XSL Working Draft
+ **/
+
+//------------------/
+//- Public Methods -/
+//------------------/
+
+/*
+ * Evaluates the given Expression and converts its result to a number.
+ */
+// static
+nsresult FunctionCall::evaluateToNumber(Expr* aExpr, txIEvalContext* aContext,
+                                        double* aResult) {
+  NS_ASSERTION(aExpr, "missing expression");
+  RefPtr<txAExprResult> exprResult;
+  nsresult rv = aExpr->evaluate(aContext, getter_AddRefs(exprResult));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  *aResult = exprResult->numberValue();
+
+  return NS_OK;
+}
+
+/*
+ * Evaluates the given Expression and converts its result to a NodeSet.
+ * If the result is not a NodeSet nullptr is returned.
+ */
+nsresult FunctionCall::evaluateToNodeSet(Expr* aExpr, txIEvalContext* aContext,
+                                         txNodeSet** aResult) {
+  NS_ASSERTION(aExpr, "Missing expression to evaluate");
+  *aResult = nullptr;
+
+  RefPtr<txAExprResult> exprRes;
+  nsresult rv = aExpr->evaluate(aContext, getter_AddRefs(exprRes));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  if (exprRes->getResultType() != txAExprResult::NODESET) {
+    aContext->receiveError(u"NodeSet expected as argument"_ns,
+                           NS_ERROR_XSLT_NODESET_EXPECTED);
+    return NS_ERROR_XSLT_NODESET_EXPECTED;
+  }
+
+  *aResult = static_cast<txNodeSet*>(static_cast<txAExprResult*>(exprRes));
+  NS_ADDREF(*aResult);
+
+  return NS_OK;
+}
+
+bool FunctionCall::requireParams(int32_t aParamCountMin, int32_t aParamCountMax,
+                                 txIEvalContext* aContext) {
+  int32_t argc = mParams.Length();
+  if (argc < aParamCountMin || (aParamCountMax > -1 && argc > aParamCountMax)) {
+    nsAutoString err(u"invalid number of parameters for function"_ns);
+#ifdef TX_TO_STRING
+    err.AppendLiteral(": ");
+    toString(err);
+#endif
+    aContext->receiveError(err, NS_ERROR_XPATH_INVALID_ARG);
+
+    return false;
+  }
+
+  return true;
+}
+
+Expr* FunctionCall::getSubExprAt(uint32_t aPos) {
+  return mParams.SafeElementAt(aPos);
+}
+
+void FunctionCall::setSubExprAt(uint32_t aPos, Expr* aExpr) {
+  NS_ASSERTION(aPos < mParams.Length(), "setting bad subexpression index");
+  mParams[aPos] = aExpr;
+}
+
+bool FunctionCall::argsSensitiveTo(ContextSensitivity aContext) {
+  uint32_t i, len = mParams.Length();
+  for (i = 0; i < len; ++i) {
+    if (mParams[i]->isSensitiveTo(aContext)) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+#ifdef TX_TO_STRING
+void FunctionCall::toString(nsAString& aDest) {
+  appendName(aDest);
+  aDest.AppendLiteral("(");
+  StringJoinAppend(
+      aDest, u","_ns, mParams,
+      [](nsAString& dest, const auto& param) { param->toString(dest); });
+  aDest.Append(char16_t(')'));
+}
+#endif
diff --git a/dom/xslt/xpath/txIXPathContext.h b/dom/xslt/xpath/txIXPathContext.h
new file mode 100644
index 0000000000..8d5b5df4be
--- /dev/null
+++ b/dom/xslt/xpath/txIXPathContext.h
@@ -0,0 +1,132 @@
+/* -*- Mode: C++; tab-width: 4; 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 __TX_I_XPATH_CONTEXT
+#define __TX_I_XPATH_CONTEXT
+
+#include "nscore.h"
+#include "nsISupportsImpl.h"
+#include "nsStringFwd.h"
+
+class FunctionCall;
+class nsAtom;
+class txAExprResult;
+class txResultRecycler;
+class txXPathNode;
+
+/*
+ * txIParseContext
+ *
+ * This interface describes the context needed to create
+ * XPath Expressions and XSLT Patters.
+ * (not completely though. key() requires the ProcessorState, which is
+ * not part of this interface.)
+ */
+
+class txIParseContext {
+ public:
+  virtual ~txIParseContext() = default;
+
+  /*
+   * Return a namespaceID for a given prefix.
+   */
+  virtual nsresult resolveNamespacePrefix(nsAtom* aPrefix, int32_t& aID) = 0;
+
+  /*
+   * Create a FunctionCall, needed for extension function calls and
+   * XSLT. XPath function calls are resolved by the Parser.
+   */
+  virtual nsresult resolveFunctionCall(nsAtom* aName, int32_t aID,
+                                       FunctionCall** aFunction) = 0;
+
+  /**
+   * Should nametests parsed in this context be case-sensitive
+   */
+  virtual bool caseInsensitiveNameTests() = 0;
+
+  /*
+   * Callback to be used by the Parser if errors are detected.
+   */
+  virtual void SetErrorOffset(uint32_t aOffset) = 0;
+
+  enum Allowed { KEY_FUNCTION = 1 << 0 };
+  virtual bool allowed(Allowed aAllowed) { return true; }
+};
+
+/*
+ * txIMatchContext
+ *
+ * Interface used for matching XSLT Patters.
+ * This is the part of txIEvalContext (see below), that is independent
+ * of the context node when evaluating a XPath expression, too.
+ * When evaluating a XPath expression, |txIMatchContext|s are used
+ * to transport the information from Step to Step.
+ */
+class txIMatchContext {
+ public:
+  virtual ~txIMatchContext() = default;
+
+  /*
+   * Return the ExprResult associated with the variable with the
+   * given namespace and local name.
+   */
+  virtual nsresult getVariable(int32_t aNamespace, nsAtom* aLName,
+                               txAExprResult*& aResult) = 0;
+
+  /*
+   * Is whitespace stripping allowed for the given node?
+   * See http://www.w3.org/TR/xslt#strip
+   */
+  virtual nsresult isStripSpaceAllowed(const txXPathNode& aNode,
+                                       bool& aAllowed) = 0;
+
+  /**
+   * Returns a pointer to the private context
+   */
+  virtual void* getPrivateContext() = 0;
+
+  virtual txResultRecycler* recycler() = 0;
+
+  /*
+   * Callback to be used by the expression/pattern if errors are detected.
+   */
+  virtual void receiveError(const nsAString& aMsg, nsresult aRes) = 0;
+};
+
+#define TX_DECL_MATCH_CONTEXT                                            \
+  nsresult getVariable(int32_t aNamespace, nsAtom* aLName,               \
+                       txAExprResult*& aResult) override;                \
+  nsresult isStripSpaceAllowed(const txXPathNode& aNode, bool& aAllowed) \
+      override;                                                          \
+  void* getPrivateContext() override;                                    \
+  txResultRecycler* recycler() override;                                 \
+  void receiveError(const nsAString& aMsg, nsresult aRes) override
+
+class txIEvalContext : public txIMatchContext {
+ public:
+  /*
+   * Get the context node.
+   */
+  virtual const txXPathNode& getContextNode() = 0;
+
+  /*
+   * Get the size of the context node set.
+   */
+  virtual uint32_t size() = 0;
+
+  /*
+   * Get the position of the context node in the context node set,
+   * starting with 1.
+   */
+  virtual uint32_t position() = 0;
+};
+
+#define TX_DECL_EVAL_CONTEXT                    \
+  TX_DECL_MATCH_CONTEXT;                        \
+  const txXPathNode& getContextNode() override; \
+  uint32_t size() override;                     \
+  uint32_t position() override
+
+#endif  // __TX_I_XPATH_CONTEXT
diff --git a/dom/xslt/xpath/txLiteralExpr.cpp b/dom/xslt/xpath/txLiteralExpr.cpp
new file mode 100644
index 0000000000..93ea2c8f1d
--- /dev/null
+++ b/dom/xslt/xpath/txLiteralExpr.cpp
@@ -0,0 +1,74 @@
+/* -*- Mode: C++; tab-width: 4; 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/. */
+
+#include "txExpr.h"
+
+nsresult txLiteralExpr::evaluate(txIEvalContext* aContext,
+                                 txAExprResult** aResult) {
+  NS_ENSURE_TRUE(mValue, NS_ERROR_OUT_OF_MEMORY);
+
+  *aResult = mValue;
+  NS_ADDREF(*aResult);
+
+  return NS_OK;
+}
+
+static Expr::ResultType resultTypes[] = {
+    Expr::NODESET_RESULT,  // NODESET
+    Expr::BOOLEAN_RESULT,  // BOOLEAN
+    Expr::NUMBER_RESULT,   // NUMBER
+    Expr::STRING_RESULT,   // STRING
+    Expr::RTF_RESULT       // RESULT_TREE_FRAGMENT
+};
+
+Expr::ResultType txLiteralExpr::getReturnType() {
+  return resultTypes[mValue->getResultType()];
+}
+
+Expr* txLiteralExpr::getSubExprAt(uint32_t aPos) { return nullptr; }
+void txLiteralExpr::setSubExprAt(uint32_t aPos, Expr* aExpr) {
+  MOZ_ASSERT_UNREACHABLE("setting bad subexpression index");
+}
+
+bool txLiteralExpr::isSensitiveTo(ContextSensitivity aContext) { return false; }
+
+#ifdef TX_TO_STRING
+void txLiteralExpr::toString(nsAString& aStr) {
+  switch (mValue->getResultType()) {
+    case txAExprResult::NODESET: {
+      aStr.AppendLiteral(" { Nodeset literal } ");
+      return;
+    }
+    case txAExprResult::BOOLEAN: {
+      if (mValue->booleanValue()) {
+        aStr.AppendLiteral("true()");
+      } else {
+        aStr.AppendLiteral("false()");
+      }
+      return;
+    }
+    case txAExprResult::NUMBER: {
+      txDouble::toString(mValue->numberValue(), aStr);
+      return;
+    }
+    case txAExprResult::STRING: {
+      StringResult* strRes =
+          static_cast<StringResult*>(static_cast<txAExprResult*>(mValue));
+      char16_t ch = '\'';
+      if (strRes->mValue.Contains(ch)) {
+        ch = '\"';
+      }
+      aStr.Append(ch);
+      aStr.Append(strRes->mValue);
+      aStr.Append(ch);
+      return;
+    }
+    case txAExprResult::RESULT_TREE_FRAGMENT: {
+      aStr.AppendLiteral(" { RTF literal } ");
+      return;
+    }
+  }
+}
+#endif
diff --git a/dom/xslt/xpath/txLocationStep.cpp b/dom/xslt/xpath/txLocationStep.cpp
new file mode 100644
index 0000000000..c10d9e8cb1
--- /dev/null
+++ b/dom/xslt/xpath/txLocationStep.cpp
@@ -0,0 +1,308 @@
+/* -*- Mode: C++; tab-width: 4; 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/. */
+
+/*
+  Implementation of an XPath LocationStep
+*/
+
+#include "txExpr.h"
+#include "txIXPathContext.h"
+#include "txNodeSet.h"
+#include "txXPathTreeWalker.h"
+
+//-----------------------------/
+//- Virtual methods from Expr -/
+//-----------------------------/
+
+/**
+ * Evaluates this Expr based on the given context node and processor state
+ * @param context the context node for evaluation of this Expr
+ * @param ps the ProcessorState containing the stack information needed
+ * for evaluation
+ * @return the result of the evaluation
+ * @see Expr
+ **/
+nsresult LocationStep::evaluate(txIEvalContext* aContext,
+                                txAExprResult** aResult) {
+  NS_ASSERTION(aContext, "internal error");
+  *aResult = nullptr;
+
+  RefPtr<txNodeSet> nodes;
+  nsresult rv = aContext->recycler()->getNodeSet(getter_AddRefs(nodes));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  txXPathTreeWalker walker(aContext->getContextNode());
+
+  switch (mAxisIdentifier) {
+    case ANCESTOR_AXIS: {
+      if (!walker.moveToParent()) {
+        break;
+      }
+      [[fallthrough]];
+    }
+    case ANCESTOR_OR_SELF_AXIS: {
+      nodes->setReverse();
+
+      do {
+        rv = appendIfMatching(walker, aContext, nodes);
+        NS_ENSURE_SUCCESS(rv, rv);
+      } while (walker.moveToParent());
+
+      break;
+    }
+    case ATTRIBUTE_AXIS: {
+      if (!walker.moveToFirstAttribute()) {
+        break;
+      }
+
+      do {
+        rv = appendIfMatching(walker, aContext, nodes);
+        NS_ENSURE_SUCCESS(rv, rv);
+      } while (walker.moveToNextAttribute());
+      break;
+    }
+    case DESCENDANT_OR_SELF_AXIS: {
+      rv = appendIfMatching(walker, aContext, nodes);
+      NS_ENSURE_SUCCESS(rv, rv);
+      [[fallthrough]];
+    }
+    case DESCENDANT_AXIS: {
+      rv = appendMatchingDescendants(walker, aContext, nodes);
+      NS_ENSURE_SUCCESS(rv, rv);
+      break;
+    }
+    case FOLLOWING_AXIS: {
+      if (txXPathNodeUtils::isAttribute(walker.getCurrentPosition())) {
+        walker.moveToParent();
+        rv = appendMatchingDescendants(walker, aContext, nodes);
+        NS_ENSURE_SUCCESS(rv, rv);
+      }
+      bool cont = true;
+      while (!walker.moveToNextSibling()) {
+        if (!walker.moveToParent()) {
+          cont = false;
+          break;
+        }
+      }
+      while (cont) {
+        rv = appendIfMatching(walker, aContext, nodes);
+        NS_ENSURE_SUCCESS(rv, rv);
+
+        rv = appendMatchingDescendants(walker, aContext, nodes);
+        NS_ENSURE_SUCCESS(rv, rv);
+
+        while (!walker.moveToNextSibling()) {
+          if (!walker.moveToParent()) {
+            cont = false;
+            break;
+          }
+        }
+      }
+      break;
+    }
+    case FOLLOWING_SIBLING_AXIS: {
+      while (walker.moveToNextSibling()) {
+        rv = appendIfMatching(walker, aContext, nodes);
+        NS_ENSURE_SUCCESS(rv, rv);
+      }
+      break;
+    }
+    case NAMESPACE_AXIS:  //-- not yet implemented
+#if 0
+            // XXX DEBUG OUTPUT
+            cout << "namespace axis not yet implemented"<<endl;
+#endif
+      break;
+    case PARENT_AXIS: {
+      if (walker.moveToParent()) {
+        rv = appendIfMatching(walker, aContext, nodes);
+        NS_ENSURE_SUCCESS(rv, rv);
+      }
+      break;
+    }
+    case PRECEDING_AXIS: {
+      nodes->setReverse();
+
+      bool cont = true;
+      while (!walker.moveToPreviousSibling()) {
+        if (!walker.moveToParent()) {
+          cont = false;
+          break;
+        }
+      }
+      while (cont) {
+        rv = appendMatchingDescendantsRev(walker, aContext, nodes);
+        NS_ENSURE_SUCCESS(rv, rv);
+
+        rv = appendIfMatching(walker, aContext, nodes);
+        NS_ENSURE_SUCCESS(rv, rv);
+
+        while (!walker.moveToPreviousSibling()) {
+          if (!walker.moveToParent()) {
+            cont = false;
+            break;
+          }
+        }
+      }
+      break;
+    }
+    case PRECEDING_SIBLING_AXIS: {
+      nodes->setReverse();
+
+      while (walker.moveToPreviousSibling()) {
+        rv = appendIfMatching(walker, aContext, nodes);
+        NS_ENSURE_SUCCESS(rv, rv);
+      }
+      break;
+    }
+    case SELF_AXIS: {
+      rv = appendIfMatching(walker, aContext, nodes);
+      NS_ENSURE_SUCCESS(rv, rv);
+      break;
+    }
+    default:  // Children Axis
+    {
+      if (!walker.moveToFirstChild()) {
+        break;
+      }
+
+      do {
+        rv = appendIfMatching(walker, aContext, nodes);
+        NS_ENSURE_SUCCESS(rv, rv);
+      } while (walker.moveToNextSibling());
+      break;
+    }
+  }
+
+  // Apply predicates
+  if (!isEmpty()) {
+    rv = evaluatePredicates(nodes, aContext);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
+  nodes->unsetReverse();
+
+  NS_ADDREF(*aResult = nodes);
+
+  return NS_OK;
+}
+
+nsresult LocationStep::appendIfMatching(const txXPathTreeWalker& aWalker,
+                                        txIMatchContext* aContext,
+                                        txNodeSet* aNodes) {
+  bool matched;
+  const txXPathNode& child = aWalker.getCurrentPosition();
+  nsresult rv = mNodeTest->matches(child, aContext, matched);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  if (matched) {
+    aNodes->append(child);
+  }
+  return NS_OK;
+}
+
+nsresult LocationStep::appendMatchingDescendants(
+    const txXPathTreeWalker& aWalker, txIMatchContext* aContext,
+    txNodeSet* aNodes) {
+  txXPathTreeWalker walker(aWalker);
+  if (!walker.moveToFirstChild()) {
+    return NS_OK;
+  }
+
+  do {
+    nsresult rv = appendIfMatching(walker, aContext, aNodes);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    rv = appendMatchingDescendants(walker, aContext, aNodes);
+    NS_ENSURE_SUCCESS(rv, rv);
+  } while (walker.moveToNextSibling());
+
+  return NS_OK;
+}
+
+nsresult LocationStep::appendMatchingDescendantsRev(
+    const txXPathTreeWalker& aWalker, txIMatchContext* aContext,
+    txNodeSet* aNodes) {
+  txXPathTreeWalker walker(aWalker);
+  if (!walker.moveToLastChild()) {
+    return NS_OK;
+  }
+
+  do {
+    nsresult rv = appendMatchingDescendantsRev(walker, aContext, aNodes);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    rv = appendIfMatching(walker, aContext, aNodes);
+    NS_ENSURE_SUCCESS(rv, rv);
+  } while (walker.moveToPreviousSibling());
+
+  return NS_OK;
+}
+
+Expr::ExprType LocationStep::getType() { return LOCATIONSTEP_EXPR; }
+
+TX_IMPL_EXPR_STUBS_BASE(LocationStep, NODESET_RESULT)
+
+Expr* LocationStep::getSubExprAt(uint32_t aPos) {
+  return PredicateList::getSubExprAt(aPos);
+}
+
+void LocationStep::setSubExprAt(uint32_t aPos, Expr* aExpr) {
+  PredicateList::setSubExprAt(aPos, aExpr);
+}
+
+bool LocationStep::isSensitiveTo(ContextSensitivity aContext) {
+  return (aContext & NODE_CONTEXT) || mNodeTest->isSensitiveTo(aContext) ||
+         PredicateList::isSensitiveTo(aContext);
+}
+
+#ifdef TX_TO_STRING
+void LocationStep::toString(nsAString& str) {
+  switch (mAxisIdentifier) {
+    case ANCESTOR_AXIS:
+      str.AppendLiteral("ancestor::");
+      break;
+    case ANCESTOR_OR_SELF_AXIS:
+      str.AppendLiteral("ancestor-or-self::");
+      break;
+    case ATTRIBUTE_AXIS:
+      str.Append(char16_t('@'));
+      break;
+    case DESCENDANT_AXIS:
+      str.AppendLiteral("descendant::");
+      break;
+    case DESCENDANT_OR_SELF_AXIS:
+      str.AppendLiteral("descendant-or-self::");
+      break;
+    case FOLLOWING_AXIS:
+      str.AppendLiteral("following::");
+      break;
+    case FOLLOWING_SIBLING_AXIS:
+      str.AppendLiteral("following-sibling::");
+      break;
+    case NAMESPACE_AXIS:
+      str.AppendLiteral("namespace::");
+      break;
+    case PARENT_AXIS:
+      str.AppendLiteral("parent::");
+      break;
+    case PRECEDING_AXIS:
+      str.AppendLiteral("preceding::");
+      break;
+    case PRECEDING_SIBLING_AXIS:
+      str.AppendLiteral("preceding-sibling::");
+      break;
+    case SELF_AXIS:
+      str.AppendLiteral("self::");
+      break;
+    default:
+      break;
+  }
+  NS_ASSERTION(mNodeTest, "mNodeTest is null, that's verboten");
+  mNodeTest->toString(str);
+
+  PredicateList::toString(str);
+}
+#endif
diff --git a/dom/xslt/xpath/txMozillaXPathTreeWalker.cpp b/dom/xslt/xpath/txMozillaXPathTreeWalker.cpp
new file mode 100644
index 0000000000..8150d7307e
--- /dev/null
+++ b/dom/xslt/xpath/txMozillaXPathTreeWalker.cpp
@@ -0,0 +1,674 @@
+/* -*- Mode: C++; tab-width: 4; 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/. */
+
+#include "txXPathTreeWalker.h"
+#include "nsAtom.h"
+#include "nsINode.h"
+#include "nsPrintfCString.h"
+#include "nsReadableUtils.h"
+#include "nsString.h"
+#include "nsTextFragment.h"
+#include "txXMLUtils.h"
+#include "txLog.h"
+#include "nsUnicharUtils.h"
+#include "nsAttrName.h"
+#include "nsNameSpaceManager.h"
+#include "nsTArray.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/dom/Attr.h"
+#include "mozilla/dom/CharacterData.h"
+#include "mozilla/dom/Element.h"
+#include <stdint.h>
+#include <algorithm>
+
+using namespace mozilla::dom;
+using mozilla::Maybe;
+
+txXPathTreeWalker::txXPathTreeWalker(const txXPathTreeWalker& aOther) = default;
+
+txXPathTreeWalker::txXPathTreeWalker(const txXPathNode& aNode)
+    : mPosition(aNode) {}
+
+void txXPathTreeWalker::moveToRoot() {
+  if (mPosition.isDocument()) {
+    return;
+  }
+
+  Document* root = mPosition.mNode->GetUncomposedDoc();
+  if (root) {
+    mPosition.mIndex = txXPathNode::eDocument;
+    mPosition.mNode = root;
+  } else {
+    nsINode* rootNode = mPosition.Root();
+
+    NS_ASSERTION(rootNode->IsContent(), "root of subtree wasn't an nsIContent");
+
+    mPosition.mIndex = txXPathNode::eContent;
+    mPosition.mNode = rootNode;
+  }
+}
+
+bool txXPathTreeWalker::moveToElementById(const nsAString& aID) {
+  if (aID.IsEmpty()) {
+    return false;
+  }
+
+  Document* doc = mPosition.mNode->GetUncomposedDoc();
+
+  nsCOMPtr<nsIContent> content;
+  if (doc) {
+    content = doc->GetElementById(aID);
+  } else {
+    // We're in a disconnected subtree, search only that subtree.
+    nsINode* rootNode = mPosition.Root();
+
+    NS_ASSERTION(rootNode->IsContent(), "root of subtree wasn't an nsIContent");
+
+    content =
+        nsContentUtils::MatchElementId(static_cast<nsIContent*>(rootNode), aID);
+  }
+
+  if (!content) {
+    return false;
+  }
+
+  mPosition.mIndex = txXPathNode::eContent;
+  mPosition.mNode = content;
+
+  return true;
+}
+
+bool txXPathTreeWalker::moveToFirstAttribute() {
+  if (!mPosition.isContent()) {
+    return false;
+  }
+
+  return moveToValidAttribute(0);
+}
+
+bool txXPathTreeWalker::moveToNextAttribute() {
+  // XXX an assertion should be enough here with the current code
+  if (!mPosition.isAttribute()) {
+    return false;
+  }
+
+  return moveToValidAttribute(mPosition.mIndex + 1);
+}
+
+bool txXPathTreeWalker::moveToValidAttribute(uint32_t aStartIndex) {
+  NS_ASSERTION(!mPosition.isDocument(), "documents doesn't have attrs");
+
+  if (!mPosition.Content()->IsElement()) {
+    return false;
+  }
+
+  Element* element = mPosition.Content()->AsElement();
+  uint32_t total = element->GetAttrCount();
+  if (aStartIndex >= total) {
+    return false;
+  }
+
+  uint32_t index;
+  for (index = aStartIndex; index < total; ++index) {
+    const nsAttrName* name = element->GetAttrNameAt(index);
+
+    // We need to ignore XMLNS attributes.
+    if (name->NamespaceID() != kNameSpaceID_XMLNS) {
+      mPosition.mIndex = index;
+
+      return true;
+    }
+  }
+  return false;
+}
+
+bool txXPathTreeWalker::moveToNamedAttribute(nsAtom* aLocalName,
+                                             int32_t aNSID) {
+  if (!mPosition.isContent() || !mPosition.Content()->IsElement()) {
+    return false;
+  }
+
+  Element* element = mPosition.Content()->AsElement();
+
+  const nsAttrName* name;
+  uint32_t i;
+  for (i = 0; (name = element->GetAttrNameAt(i)); ++i) {
+    if (name->Equals(aLocalName, aNSID)) {
+      mPosition.mIndex = i;
+
+      return true;
+    }
+  }
+  return false;
+}
+
+bool txXPathTreeWalker::moveToFirstChild() {
+  if (mPosition.isAttribute()) {
+    return false;
+  }
+
+  nsIContent* child = mPosition.mNode->GetFirstChild();
+  if (!child) {
+    return false;
+  }
+  mPosition.mIndex = txXPathNode::eContent;
+  mPosition.mNode = child;
+
+  return true;
+}
+
+bool txXPathTreeWalker::moveToLastChild() {
+  if (mPosition.isAttribute()) {
+    return false;
+  }
+
+  nsIContent* child = mPosition.mNode->GetLastChild();
+  if (!child) {
+    return false;
+  }
+
+  mPosition.mIndex = txXPathNode::eContent;
+  mPosition.mNode = child;
+
+  return true;
+}
+
+bool txXPathTreeWalker::moveToNextSibling() {
+  if (!mPosition.isContent()) {
+    return false;
+  }
+
+  nsINode* sibling = mPosition.mNode->GetNextSibling();
+  if (!sibling) {
+    return false;
+  }
+
+  mPosition.mNode = sibling;
+
+  return true;
+}
+
+bool txXPathTreeWalker::moveToPreviousSibling() {
+  if (!mPosition.isContent()) {
+    return false;
+  }
+
+  nsINode* sibling = mPosition.mNode->GetPreviousSibling();
+  if (!sibling) {
+    return false;
+  }
+
+  mPosition.mNode = sibling;
+
+  return true;
+}
+
+bool txXPathTreeWalker::moveToParent() {
+  if (mPosition.isDocument()) {
+    return false;
+  }
+
+  if (mPosition.isAttribute()) {
+    mPosition.mIndex = txXPathNode::eContent;
+
+    return true;
+  }
+
+  nsINode* parent = mPosition.mNode->GetParentNode();
+  if (!parent) {
+    return false;
+  }
+
+  mPosition.mIndex = mPosition.mNode->GetParent() ? txXPathNode::eContent
+                                                  : txXPathNode::eDocument;
+  mPosition.mNode = parent;
+
+  return true;
+}
+
+txXPathNode::txXPathNode(const txXPathNode& aNode)
+    : mNode(aNode.mNode),
+      mRefCountRoot(aNode.mRefCountRoot),
+      mIndex(aNode.mIndex) {
+  MOZ_COUNT_CTOR(txXPathNode);
+  if (mRefCountRoot) {
+    NS_ADDREF(Root());
+  }
+}
+
+txXPathNode::~txXPathNode() {
+  MOZ_COUNT_DTOR(txXPathNode);
+  if (mRefCountRoot) {
+    nsINode* root = Root();
+    NS_RELEASE(root);
+  }
+}
+
+/* static */
+bool txXPathNodeUtils::getAttr(const txXPathNode& aNode, nsAtom* aLocalName,
+                               int32_t aNSID, nsAString& aValue) {
+  if (aNode.isDocument() || aNode.isAttribute() ||
+      !aNode.Content()->IsElement()) {
+    return false;
+  }
+
+  return aNode.Content()->AsElement()->GetAttr(aNSID, aLocalName, aValue);
+}
+
+/* static */
+already_AddRefed<nsAtom> txXPathNodeUtils::getLocalName(
+    const txXPathNode& aNode) {
+  if (aNode.isDocument()) {
+    return nullptr;
+  }
+
+  if (aNode.isContent()) {
+    if (aNode.mNode->IsElement()) {
+      RefPtr<nsAtom> localName = aNode.Content()->NodeInfo()->NameAtom();
+      return localName.forget();
+    }
+
+    if (aNode.mNode->IsProcessingInstruction()) {
+      return NS_Atomize(aNode.mNode->NodeName());
+    }
+
+    return nullptr;
+  }
+
+  // This is an attribute node, so we necessarily come from an element.
+  RefPtr<nsAtom> localName =
+      aNode.Content()->AsElement()->GetAttrNameAt(aNode.mIndex)->LocalName();
+
+  return localName.forget();
+}
+
+nsAtom* txXPathNodeUtils::getPrefix(const txXPathNode& aNode) {
+  if (aNode.isDocument()) {
+    return nullptr;
+  }
+
+  if (aNode.isContent()) {
+    // All other nsIContent node types but elements have a null prefix
+    // which is what we want here.
+    return aNode.Content()->NodeInfo()->GetPrefixAtom();
+  }
+
+  return aNode.Content()->AsElement()->GetAttrNameAt(aNode.mIndex)->GetPrefix();
+}
+
+/* static */
+void txXPathNodeUtils::getLocalName(const txXPathNode& aNode,
+                                    nsAString& aLocalName) {
+  if (aNode.isDocument()) {
+    aLocalName.Truncate();
+
+    return;
+  }
+
+  if (aNode.isContent()) {
+    if (aNode.mNode->IsElement()) {
+      mozilla::dom::NodeInfo* nodeInfo = aNode.Content()->NodeInfo();
+      nodeInfo->GetName(aLocalName);
+      return;
+    }
+
+    if (aNode.mNode->IsProcessingInstruction()) {
+      // PIs don't have a nodeinfo but do have a name
+      // XXXbz Not actually true, but this function looks like it wants
+      // different things from elements and PIs for "local name"...
+      aLocalName = aNode.mNode->NodeName();
+      return;
+    }
+
+    aLocalName.Truncate();
+
+    return;
+  }
+
+  aNode.Content()
+      ->AsElement()
+      ->GetAttrNameAt(aNode.mIndex)
+      ->LocalName()
+      ->ToString(aLocalName);
+
+  // Check for html
+  if (aNode.Content()->NodeInfo()->NamespaceEquals(kNameSpaceID_None) &&
+      aNode.Content()->IsHTMLElement()) {
+    nsContentUtils::ASCIIToUpper(aLocalName);
+  }
+}
+
+/* static */
+void txXPathNodeUtils::getNodeName(const txXPathNode& aNode, nsAString& aName) {
+  if (aNode.isDocument()) {
+    aName.Truncate();
+
+    return;
+  }
+
+  if (aNode.isContent()) {
+    // Elements and PIs have a name
+    if (aNode.mNode->IsElement() ||
+        aNode.mNode->NodeType() == nsINode::PROCESSING_INSTRUCTION_NODE) {
+      aName = aNode.Content()->NodeName();
+      return;
+    }
+
+    aName.Truncate();
+
+    return;
+  }
+
+  aNode.Content()
+      ->AsElement()
+      ->GetAttrNameAt(aNode.mIndex)
+      ->GetQualifiedName(aName);
+}
+
+/* static */
+int32_t txXPathNodeUtils::getNamespaceID(const txXPathNode& aNode) {
+  if (aNode.isDocument()) {
+    return kNameSpaceID_None;
+  }
+
+  if (aNode.isContent()) {
+    return aNode.Content()->GetNameSpaceID();
+  }
+
+  return aNode.Content()
+      ->AsElement()
+      ->GetAttrNameAt(aNode.mIndex)
+      ->NamespaceID();
+}
+
+/* static */
+void txXPathNodeUtils::getNamespaceURI(const txXPathNode& aNode,
+                                       nsAString& aURI) {
+  nsNameSpaceManager::GetInstance()->GetNameSpaceURI(getNamespaceID(aNode),
+                                                     aURI);
+}
+
+/* static */
+uint16_t txXPathNodeUtils::getNodeType(const txXPathNode& aNode) {
+  if (aNode.isDocument()) {
+    return txXPathNodeType::DOCUMENT_NODE;
+  }
+
+  if (aNode.isContent()) {
+    return aNode.mNode->NodeType();
+  }
+
+  return txXPathNodeType::ATTRIBUTE_NODE;
+}
+
+/* static */
+void txXPathNodeUtils::appendNodeValue(const txXPathNode& aNode,
+                                       nsAString& aResult) {
+  if (aNode.isAttribute()) {
+    const nsAttrName* name =
+        aNode.Content()->AsElement()->GetAttrNameAt(aNode.mIndex);
+
+    if (aResult.IsEmpty()) {
+      aNode.Content()->AsElement()->GetAttr(name->NamespaceID(),
+                                            name->LocalName(), aResult);
+    } else {
+      nsAutoString result;
+      aNode.Content()->AsElement()->GetAttr(name->NamespaceID(),
+                                            name->LocalName(), result);
+      aResult.Append(result);
+    }
+
+    return;
+  }
+
+  if (aNode.isDocument() || aNode.mNode->IsElement() ||
+      aNode.mNode->IsDocumentFragment()) {
+    nsContentUtils::AppendNodeTextContent(aNode.mNode, true, aResult,
+                                          mozilla::fallible);
+
+    return;
+  }
+
+  MOZ_ASSERT(aNode.mNode->IsCharacterData());
+  static_cast<CharacterData*>(aNode.Content())->AppendTextTo(aResult);
+}
+
+/* static */
+bool txXPathNodeUtils::isWhitespace(const txXPathNode& aNode) {
+  NS_ASSERTION(aNode.isContent() && isText(aNode), "Wrong type!");
+
+  return aNode.Content()->TextIsOnlyWhitespace();
+}
+
+/* static */
+txXPathNode* txXPathNodeUtils::getOwnerDocument(const txXPathNode& aNode) {
+  return new txXPathNode(aNode.mNode->OwnerDoc());
+}
+
+const char gPrintfFmt[] = "id0x%" PRIxPTR;
+const char gPrintfFmtAttr[] = "id0x%" PRIxPTR "-%010i";
+
+/* static */
+nsresult txXPathNodeUtils::getXSLTId(const txXPathNode& aNode,
+                                     const txXPathNode& aBase,
+                                     nsAString& aResult) {
+  uintptr_t nodeid = ((uintptr_t)aNode.mNode) - ((uintptr_t)aBase.mNode);
+  if (!aNode.isAttribute()) {
+    CopyASCIItoUTF16(nsPrintfCString(gPrintfFmt, nodeid), aResult);
+  } else {
+    CopyASCIItoUTF16(nsPrintfCString(gPrintfFmtAttr, nodeid, aNode.mIndex),
+                     aResult);
+  }
+
+  return NS_OK;
+}
+
+/* static */
+nsresult txXPathNodeUtils::getBaseURI(const txXPathNode& aNode,
+                                      nsAString& aURI) {
+  return aNode.mNode->GetBaseURI(aURI);
+}
+
+/* static */
+int txXPathNodeUtils::comparePosition(const txXPathNode& aNode,
+                                      const txXPathNode& aOtherNode) {
+  // First check for equal nodes or attribute-nodes on the same element.
+  if (aNode.mNode == aOtherNode.mNode) {
+    if (aNode.mIndex == aOtherNode.mIndex) {
+      return 0;
+    }
+
+    NS_ASSERTION(!aNode.isDocument() && !aOtherNode.isDocument(),
+                 "documents should always have a set index");
+
+    if (aNode.isContent() ||
+        (!aOtherNode.isContent() && aNode.mIndex < aOtherNode.mIndex)) {
+      return -1;
+    }
+
+    return 1;
+  }
+
+  // Get document for both nodes.
+  Document* document = aNode.mNode->GetUncomposedDoc();
+  Document* otherDocument = aOtherNode.mNode->GetUncomposedDoc();
+
+  // If the nodes have different current documents, compare the document
+  // pointers.
+  if (document != otherDocument) {
+    return document < otherDocument ? -1 : 1;
+  }
+
+  // Now either both nodes are in orphan trees, or they are both in the
+  // same tree.
+
+  // Get parents up the tree.
+  AutoTArray<nsINode*, 8> parents, otherParents;
+  nsINode* node = aNode.mNode;
+  nsINode* otherNode = aOtherNode.mNode;
+  nsINode* parent;
+  nsINode* otherParent;
+  while (node && otherNode) {
+    parent = node->GetParentNode();
+    otherParent = otherNode->GetParentNode();
+
+    // Hopefully this is a common case.
+    if (parent == otherParent) {
+      if (!parent) {
+        // Both node and otherNode are root nodes in respective orphan
+        // tree.
+        return node < otherNode ? -1 : 1;
+      }
+
+      const Maybe<uint32_t> indexOfNode = parent->ComputeIndexOf(node);
+      const Maybe<uint32_t> indexOfOtherNode =
+          parent->ComputeIndexOf(otherNode);
+      if (MOZ_LIKELY(indexOfNode.isSome() && indexOfOtherNode.isSome())) {
+        return *indexOfNode < *indexOfOtherNode ? -1 : 1;
+      }
+      // XXX Keep the odd traditional behavior for now.
+      return indexOfNode.isNothing() && indexOfOtherNode.isSome() ? -1 : 1;
+    }
+
+    parents.AppendElement(node);
+    otherParents.AppendElement(otherNode);
+    node = parent;
+    otherNode = otherParent;
+  }
+
+  while (node) {
+    parents.AppendElement(node);
+    node = node->GetParentNode();
+  }
+  while (otherNode) {
+    otherParents.AppendElement(otherNode);
+    otherNode = otherNode->GetParentNode();
+  }
+
+  // Walk back down along the parent-chains until we find where they split.
+  int32_t total = parents.Length() - 1;
+  int32_t otherTotal = otherParents.Length() - 1;
+  NS_ASSERTION(total != otherTotal, "Can't have same number of parents");
+
+  int32_t lastIndex = std::min(total, otherTotal);
+  int32_t i;
+  parent = nullptr;
+  for (i = 0; i <= lastIndex; ++i) {
+    node = parents.ElementAt(total - i);
+    otherNode = otherParents.ElementAt(otherTotal - i);
+    if (node != otherNode) {
+      if (!parent) {
+        // The two nodes are in different orphan subtrees.
+        NS_ASSERTION(i == 0, "this shouldn't happen");
+        return node < otherNode ? -1 : 1;
+      }
+
+      const Maybe<uint32_t> index = parent->ComputeIndexOf(node);
+      const Maybe<uint32_t> otherIndex = parent->ComputeIndexOf(otherNode);
+      if (MOZ_LIKELY(index.isSome() && otherIndex.isSome())) {
+        NS_ASSERTION(*index != *otherIndex, "invalid index in comparePosition");
+        return *index < *otherIndex ? -1 : 1;
+      }
+      NS_ASSERTION(false, "invalid index in comparePosition");
+      // XXX Keep the odd traditional behavior for now.
+      return index.isNothing() && otherIndex.isSome() ? -1 : 1;
+    }
+
+    parent = node;
+  }
+
+  // One node is a descendant of the other. The one with the shortest
+  // parent-chain is first in the document.
+  return total < otherTotal ? -1 : 1;
+}
+
+/* static */
+txXPathNode* txXPathNativeNode::createXPathNode(nsIContent* aContent,
+                                                bool aKeepRootAlive) {
+  nsINode* root = aKeepRootAlive ? txXPathNode::RootOf(aContent) : nullptr;
+
+  return new txXPathNode(aContent, txXPathNode::eContent, root);
+}
+
+/* static */
+txXPathNode* txXPathNativeNode::createXPathNode(nsINode* aNode,
+                                                bool aKeepRootAlive) {
+  uint16_t nodeType = aNode->NodeType();
+  if (nodeType == nsINode::ATTRIBUTE_NODE) {
+    auto* attr = static_cast<Attr*>(aNode);
+
+    NodeInfo* nodeInfo = attr->NodeInfo();
+    Element* parent = attr->GetElement();
+    if (!parent) {
+      return nullptr;
+    }
+
+    nsINode* root = aKeepRootAlive ? txXPathNode::RootOf(parent) : nullptr;
+
+    uint32_t i, total = parent->GetAttrCount();
+    for (i = 0; i < total; ++i) {
+      const nsAttrName* name = parent->GetAttrNameAt(i);
+      if (nodeInfo->Equals(name->LocalName(), name->NamespaceID())) {
+        return new txXPathNode(parent, i, root);
+      }
+    }
+
+    NS_ERROR("Couldn't find the attribute in its parent!");
+
+    return nullptr;
+  }
+
+  uint32_t index;
+  nsINode* root = aKeepRootAlive ? aNode : nullptr;
+
+  if (nodeType == nsINode::DOCUMENT_NODE) {
+    index = txXPathNode::eDocument;
+  } else {
+    index = txXPathNode::eContent;
+    if (root) {
+      root = txXPathNode::RootOf(root);
+    }
+  }
+
+  return new txXPathNode(aNode, index, root);
+}
+
+/* static */
+txXPathNode* txXPathNativeNode::createXPathNode(Document* aDocument) {
+  return new txXPathNode(aDocument);
+}
+
+/* static */
+nsINode* txXPathNativeNode::getNode(const txXPathNode& aNode) {
+  if (!aNode.isAttribute()) {
+    return aNode.mNode;
+  }
+
+  const nsAttrName* name =
+      aNode.Content()->AsElement()->GetAttrNameAt(aNode.mIndex);
+
+  nsAutoString namespaceURI;
+  nsNameSpaceManager::GetInstance()->GetNameSpaceURI(name->NamespaceID(),
+                                                     namespaceURI);
+
+  nsCOMPtr<Element> element = do_QueryInterface(aNode.mNode);
+  nsDOMAttributeMap* map = element->Attributes();
+  return map->GetNamedItemNS(namespaceURI,
+                             nsDependentAtomString(name->LocalName()));
+}
+
+/* static */
+nsIContent* txXPathNativeNode::getContent(const txXPathNode& aNode) {
+  NS_ASSERTION(aNode.isContent(),
+               "Only call getContent on nsIContent wrappers!");
+  return aNode.Content();
+}
+
+/* static */
+Document* txXPathNativeNode::getDocument(const txXPathNode& aNode) {
+  NS_ASSERTION(aNode.isDocument(),
+               "Only call getDocument on Document wrappers!");
+  return aNode.Document();
+}
diff --git a/dom/xslt/xpath/txNameTest.cpp b/dom/xslt/xpath/txNameTest.cpp
new file mode 100644
index 0000000000..f76113146c
--- /dev/null
+++ b/dom/xslt/xpath/txNameTest.cpp
@@ -0,0 +1,92 @@
+/* -*- Mode: C++; tab-width: 4; 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/. */
+
+#include "txExpr.h"
+#include "nsAtom.h"
+#include "nsGkAtoms.h"
+#include "txXPathTreeWalker.h"
+#include "txIXPathContext.h"
+
+txNameTest::txNameTest(nsAtom* aPrefix, nsAtom* aLocalName, int32_t aNSID,
+                       uint16_t aNodeType)
+    : mPrefix(aPrefix),
+      mLocalName(aLocalName),
+      mNamespace(aNSID),
+      mNodeType(aNodeType) {
+  if (aPrefix == nsGkAtoms::_empty) mPrefix = nullptr;
+  NS_ASSERTION(aLocalName, "txNameTest without a local name?");
+  NS_ASSERTION(aNodeType == txXPathNodeType::DOCUMENT_NODE ||
+                   aNodeType == txXPathNodeType::ELEMENT_NODE ||
+                   aNodeType == txXPathNodeType::ATTRIBUTE_NODE,
+               "Go fix txNameTest::matches");
+}
+
+nsresult txNameTest::matches(const txXPathNode& aNode,
+                             txIMatchContext* aContext, bool& aMatched) {
+  if ((mNodeType == txXPathNodeType::ELEMENT_NODE &&
+       !txXPathNodeUtils::isElement(aNode)) ||
+      (mNodeType == txXPathNodeType::ATTRIBUTE_NODE &&
+       !txXPathNodeUtils::isAttribute(aNode)) ||
+      (mNodeType == txXPathNodeType::DOCUMENT_NODE &&
+       !txXPathNodeUtils::isRoot(aNode))) {
+    aMatched = false;
+    return NS_OK;
+  }
+
+  // Totally wild?
+  if (mLocalName == nsGkAtoms::_asterisk && !mPrefix) {
+    aMatched = true;
+    return NS_OK;
+  }
+
+  // Compare namespaces
+  if (mNamespace != txXPathNodeUtils::getNamespaceID(aNode) &&
+      !(mNamespace == kNameSpaceID_None &&
+        txXPathNodeUtils::isHTMLElementInHTMLDocument(aNode))) {
+    aMatched = false;
+    return NS_OK;
+  }
+
+  // Name wild?
+  if (mLocalName == nsGkAtoms::_asterisk) {
+    aMatched = true;
+    return NS_OK;
+  }
+
+  // Compare local-names
+  aMatched = txXPathNodeUtils::localNameEquals(aNode, mLocalName);
+  return NS_OK;
+}
+
+/*
+ * Returns the default priority of this txNodeTest
+ */
+double txNameTest::getDefaultPriority() {
+  if (mLocalName == nsGkAtoms::_asterisk) {
+    if (!mPrefix) return -0.5;
+    return -0.25;
+  }
+  return 0;
+}
+
+txNodeTest::NodeTestType txNameTest::getType() { return NAME_TEST; }
+
+bool txNameTest::isSensitiveTo(Expr::ContextSensitivity aContext) {
+  return !!(aContext & Expr::NODE_CONTEXT);
+}
+
+#ifdef TX_TO_STRING
+void txNameTest::toString(nsAString& aDest) {
+  if (mPrefix) {
+    nsAutoString prefix;
+    mPrefix->ToString(prefix);
+    aDest.Append(prefix);
+    aDest.Append(char16_t(':'));
+  }
+  nsAutoString localName;
+  mLocalName->ToString(localName);
+  aDest.Append(localName);
+}
+#endif
diff --git a/dom/xslt/xpath/txNamedAttributeStep.cpp b/dom/xslt/xpath/txNamedAttributeStep.cpp
new file mode 100644
index 0000000000..18938e1dd3
--- /dev/null
+++ b/dom/xslt/xpath/txNamedAttributeStep.cpp
@@ -0,0 +1,53 @@
+/* -*- Mode: C++; tab-width: 4; 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/. */
+
+#include "nsAtom.h"
+#include "txIXPathContext.h"
+#include "txNodeSet.h"
+#include "txExpr.h"
+#include "txXPathTreeWalker.h"
+
+txNamedAttributeStep::txNamedAttributeStep(int32_t aNsID, nsAtom* aPrefix,
+                                           nsAtom* aLocalName)
+    : mNamespace(aNsID), mPrefix(aPrefix), mLocalName(aLocalName) {}
+
+nsresult txNamedAttributeStep::evaluate(txIEvalContext* aContext,
+                                        txAExprResult** aResult) {
+  *aResult = nullptr;
+
+  RefPtr<txNodeSet> nodes;
+  nsresult rv = aContext->recycler()->getNodeSet(getter_AddRefs(nodes));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  txXPathTreeWalker walker(aContext->getContextNode());
+  if (walker.moveToNamedAttribute(mLocalName, mNamespace)) {
+    rv = nodes->append(walker.getCurrentPosition());
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+  NS_ADDREF(*aResult = nodes);
+
+  return NS_OK;
+}
+
+TX_IMPL_EXPR_STUBS_0(txNamedAttributeStep, NODESET_RESULT)
+
+bool txNamedAttributeStep::isSensitiveTo(ContextSensitivity aContext) {
+  return !!(aContext & NODE_CONTEXT);
+}
+
+#ifdef TX_TO_STRING
+void txNamedAttributeStep::toString(nsAString& aDest) {
+  aDest.Append(char16_t('@'));
+  if (mPrefix) {
+    nsAutoString prefix;
+    mPrefix->ToString(prefix);
+    aDest.Append(prefix);
+    aDest.Append(char16_t(':'));
+  }
+  nsAutoString localName;
+  mLocalName->ToString(localName);
+  aDest.Append(localName);
+}
+#endif
diff --git a/dom/xslt/xpath/txNodeSet.cpp b/dom/xslt/xpath/txNodeSet.cpp
new file mode 100644
index 0000000000..60eed8952d
--- /dev/null
+++ b/dom/xslt/xpath/txNodeSet.cpp
@@ -0,0 +1,567 @@
+/* -*- Mode: C++; tab-width: 4; 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/. */
+
+#include "txNodeSet.h"
+#include "txLog.h"
+#include "txXPathTreeWalker.h"
+#include <algorithm>
+
+/**
+ * Implementation of an XPath nodeset
+ */
+
+#ifdef NS_BUILD_REFCNT_LOGGING
+#  define LOG_CHUNK_MOVE(_start, _new_start, _count)         \
+    {                                                        \
+      txXPathNode* start = const_cast<txXPathNode*>(_start); \
+      while (start < _start + _count) {                      \
+        NS_LogDtor(start, "txXPathNode", sizeof(*start));    \
+        ++start;                                             \
+      }                                                      \
+      start = const_cast<txXPathNode*>(_new_start);          \
+      while (start < _new_start + _count) {                  \
+        NS_LogCtor(start, "txXPathNode", sizeof(*start));    \
+        ++start;                                             \
+      }                                                      \
+    }
+#else
+#  define LOG_CHUNK_MOVE(_start, _new_start, _count)
+#endif
+
+static const int32_t kTxNodeSetMinSize = 4;
+static const int32_t kTxNodeSetGrowFactor = 2;
+
+#define kForward 1
+#define kReversed -1
+
+txNodeSet::txNodeSet(txResultRecycler* aRecycler)
+    : txAExprResult(aRecycler),
+      mStart(nullptr),
+      mEnd(nullptr),
+      mStartBuffer(nullptr),
+      mEndBuffer(nullptr),
+      mDirection(kForward),
+      mMarks(nullptr) {}
+
+txNodeSet::txNodeSet(const txXPathNode& aNode, txResultRecycler* aRecycler)
+    : txAExprResult(aRecycler),
+      mStart(nullptr),
+      mEnd(nullptr),
+      mStartBuffer(nullptr),
+      mEndBuffer(nullptr),
+      mDirection(kForward),
+      mMarks(nullptr) {
+  if (!ensureGrowSize(1)) {
+    return;
+  }
+
+  new (mStart) txXPathNode(aNode);
+  ++mEnd;
+}
+
+txNodeSet::txNodeSet(const txNodeSet& aSource, txResultRecycler* aRecycler)
+    : txAExprResult(aRecycler),
+      mStart(nullptr),
+      mEnd(nullptr),
+      mStartBuffer(nullptr),
+      mEndBuffer(nullptr),
+      mDirection(kForward),
+      mMarks(nullptr) {
+  append(aSource);
+}
+
+txNodeSet::~txNodeSet() {
+  delete[] mMarks;
+
+  if (mStartBuffer) {
+    destroyElements(mStart, mEnd);
+
+    free(mStartBuffer);
+  }
+}
+
+nsresult txNodeSet::add(const txXPathNode& aNode) {
+  NS_ASSERTION(mDirection == kForward,
+               "only append(aNode) is supported on reversed nodesets");
+
+  if (isEmpty()) {
+    return append(aNode);
+  }
+
+  bool dupe;
+  txXPathNode* pos = findPosition(aNode, mStart, mEnd, dupe);
+
+  if (dupe) {
+    return NS_OK;
+  }
+
+  // save pos, ensureGrowSize messes with the pointers
+  int32_t moveSize = mEnd - pos;
+  int32_t offset = pos - mStart;
+  if (!ensureGrowSize(1)) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+  // set pos to where it was
+  pos = mStart + offset;
+
+  if (moveSize > 0) {
+    LOG_CHUNK_MOVE(pos, pos + 1, moveSize);
+    memmove(pos + 1, pos, moveSize * sizeof(txXPathNode));
+  }
+
+  new (pos) txXPathNode(aNode);
+  ++mEnd;
+
+  return NS_OK;
+}
+
+nsresult txNodeSet::add(const txNodeSet& aNodes) {
+  return add(aNodes, copyElements, nullptr);
+}
+
+nsresult txNodeSet::addAndTransfer(txNodeSet* aNodes) {
+  // failure is out-of-memory, transfer didn't happen
+  nsresult rv = add(*aNodes, transferElements, destroyElements);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+#ifdef TX_DONT_RECYCLE_BUFFER
+  if (aNodes->mStartBuffer) {
+    free(aNodes->mStartBuffer);
+    aNodes->mStartBuffer = aNodes->mEndBuffer = nullptr;
+  }
+#endif
+  aNodes->mStart = aNodes->mEnd = aNodes->mStartBuffer;
+
+  return NS_OK;
+}
+
+/**
+ * add(aNodeSet, aTransferOp)
+ *
+ * The code is optimized to make a minimum number of calls to
+ * Node::compareDocumentPosition. The idea is this:
+ * We have the two nodesets (number indicate "document position")
+ *
+ * 1 3 7             <- source 1
+ * 2 3 6 8 9         <- source 2
+ * _ _ _ _ _ _ _ _   <- result
+ *
+ *
+ * When merging these nodesets into the result, the nodes are transfered
+ * in chunks to the end of the buffer so that each chunk does not contain
+ * a node from the other nodeset, in document order.
+ *
+ * We select the last non-transfered node in the first nodeset and find
+ * where in the other nodeset it would be inserted. In this case we would
+ * take the 7 from the first nodeset and find the position between the
+ * 6 and 8 in the second. We then take the nodes after the insert-position
+ * and transfer them to the end of the resulting nodeset. Which in this case
+ * means that we first transfered the 8 and 9 nodes, giving us the following:
+ *
+ * 1 3 7             <- source 1
+ * 2 3 6             <- source 2
+ * _ _ _ _ _ _ 8 9   <- result
+ *
+ * The corresponding procedure is done for the second nodeset, that is
+ * the insertion position of the 6 in the first nodeset is found, which
+ * is between the 3 and the 7. The 7 is memmoved (as it stays within
+ * the same nodeset) to the result buffer.
+ *
+ * As the result buffer is filled from the end, it is safe to share the
+ * buffer between this nodeset and the result.
+ *
+ * This is repeated until both of the nodesets are empty.
+ *
+ * If we find a duplicate node when searching for where insertposition we
+ * check for sequences of duplicate nodes, which can be optimized.
+ *
+ */
+nsresult txNodeSet::add(const txNodeSet& aNodes, transferOp aTransfer,
+                        destroyOp aDestroy) {
+  NS_ASSERTION(mDirection == kForward,
+               "only append(aNode) is supported on reversed nodesets");
+
+  if (aNodes.isEmpty()) {
+    return NS_OK;
+  }
+
+  if (!ensureGrowSize(aNodes.size())) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  // This is probably a rather common case, so lets try to shortcut.
+  if (mStart == mEnd ||
+      txXPathNodeUtils::comparePosition(mEnd[-1], *aNodes.mStart) < 0) {
+    aTransfer(mEnd, aNodes.mStart, aNodes.mEnd);
+    mEnd += aNodes.size();
+
+    return NS_OK;
+  }
+
+  // Last element in this nodeset
+  txXPathNode* thisPos = mEnd;
+
+  // Last element of the other nodeset
+  txXPathNode* otherPos = aNodes.mEnd;
+
+  // Pointer to the insertion point in this nodeset
+  txXPathNode* insertPos = mEndBuffer;
+
+  bool dupe;
+  txXPathNode* pos;
+  int32_t count;
+  while (thisPos > mStart || otherPos > aNodes.mStart) {
+    // Find where the last remaining node of this nodeset would
+    // be inserted in the other nodeset.
+    if (thisPos > mStart) {
+      pos = findPosition(thisPos[-1], aNodes.mStart, otherPos, dupe);
+
+      if (dupe) {
+        const txXPathNode* deletePos = thisPos;
+        --thisPos;  // this is already added
+        // check dupe sequence
+        while (thisPos > mStart && pos > aNodes.mStart &&
+               thisPos[-1] == pos[-1]) {
+          --thisPos;
+          --pos;
+        }
+
+        if (aDestroy) {
+          aDestroy(thisPos, deletePos);
+        }
+      }
+    } else {
+      pos = aNodes.mStart;
+    }
+
+    // Transfer the otherNodes after the insertion point to the result
+    count = otherPos - pos;
+    if (count > 0) {
+      insertPos -= count;
+      aTransfer(insertPos, pos, otherPos);
+      otherPos -= count;
+    }
+
+    // Find where the last remaining node of the otherNodeset would
+    // be inserted in this nodeset.
+    if (otherPos > aNodes.mStart) {
+      pos = findPosition(otherPos[-1], mStart, thisPos, dupe);
+
+      if (dupe) {
+        const txXPathNode* deletePos = otherPos;
+        --otherPos;  // this is already added
+        // check dupe sequence
+        while (otherPos > aNodes.mStart && pos > mStart &&
+               otherPos[-1] == pos[-1]) {
+          --otherPos;
+          --pos;
+        }
+
+        if (aDestroy) {
+          aDestroy(otherPos, deletePos);
+        }
+      }
+    } else {
+      pos = mStart;
+    }
+
+    // Move the nodes from this nodeset after the insertion point
+    // to the result
+    count = thisPos - pos;
+    if (count > 0) {
+      insertPos -= count;
+      LOG_CHUNK_MOVE(pos, insertPos, count);
+      memmove(insertPos, pos, count * sizeof(txXPathNode));
+      thisPos -= count;
+    }
+  }
+  mStart = insertPos;
+  mEnd = mEndBuffer;
+
+  return NS_OK;
+}
+
+/**
+ * Append API
+ * These functions should be used with care.
+ * They are intended to be used when the caller assures that the resulting
+ * nodeset remains in document order.
+ * Abuse will break document order, and cause errors in the result.
+ * These functions are significantly faster than the add API, as no
+ * order info operations will be performed.
+ */
+
+nsresult txNodeSet::append(const txXPathNode& aNode) {
+  if (!ensureGrowSize(1)) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  if (mDirection == kForward) {
+    new (mEnd) txXPathNode(aNode);
+    ++mEnd;
+
+    return NS_OK;
+  }
+
+  new (--mStart) txXPathNode(aNode);
+
+  return NS_OK;
+}
+
+nsresult txNodeSet::append(const txNodeSet& aNodes) {
+  NS_ASSERTION(mDirection == kForward,
+               "only append(aNode) is supported on reversed nodesets");
+
+  if (aNodes.isEmpty()) {
+    return NS_OK;
+  }
+
+  int32_t appended = aNodes.size();
+  if (!ensureGrowSize(appended)) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  copyElements(mEnd, aNodes.mStart, aNodes.mEnd);
+  mEnd += appended;
+
+  return NS_OK;
+}
+
+nsresult txNodeSet::mark(int32_t aIndex) {
+  NS_ASSERTION(aIndex >= 0 && mStart && mEnd - mStart > aIndex,
+               "index out of bounds");
+  if (!mMarks) {
+    int32_t length = size();
+    mMarks = new bool[length];
+    memset(mMarks, 0, length * sizeof(bool));
+  }
+  if (mDirection == kForward) {
+    mMarks[aIndex] = true;
+  } else {
+    mMarks[size() - aIndex - 1] = true;
+  }
+
+  return NS_OK;
+}
+
+nsresult txNodeSet::sweep() {
+  if (!mMarks) {
+    // sweep everything
+    clear();
+  }
+
+  int32_t chunk, pos = 0;
+  int32_t length = size();
+  txXPathNode* insertion = mStartBuffer;
+
+  while (pos < length) {
+    while (pos < length && !mMarks[pos]) {
+      // delete unmarked
+      mStart[pos].~txXPathNode();
+      ++pos;
+    }
+    // find chunk to move
+    chunk = 0;
+    while (pos < length && mMarks[pos]) {
+      ++pos;
+      ++chunk;
+    }
+    // move chunk
+    if (chunk > 0) {
+      LOG_CHUNK_MOVE(mStart + pos - chunk, insertion, chunk);
+      memmove(insertion, mStart + pos - chunk, chunk * sizeof(txXPathNode));
+      insertion += chunk;
+    }
+  }
+  mStart = mStartBuffer;
+  mEnd = insertion;
+  delete[] mMarks;
+  mMarks = nullptr;
+
+  return NS_OK;
+}
+
+void txNodeSet::clear() {
+  destroyElements(mStart, mEnd);
+#ifdef TX_DONT_RECYCLE_BUFFER
+  if (mStartBuffer) {
+    free(mStartBuffer);
+    mStartBuffer = mEndBuffer = nullptr;
+  }
+#endif
+  mStart = mEnd = mStartBuffer;
+  delete[] mMarks;
+  mMarks = nullptr;
+  mDirection = kForward;
+}
+
+int32_t txNodeSet::indexOf(const txXPathNode& aNode, uint32_t aStart) const {
+  NS_ASSERTION(mDirection == kForward,
+               "only append(aNode) is supported on reversed nodesets");
+
+  if (!mStart || mStart == mEnd) {
+    return -1;
+  }
+
+  txXPathNode* pos = mStart + aStart;
+  for (; pos < mEnd; ++pos) {
+    if (*pos == aNode) {
+      return pos - mStart;
+    }
+  }
+
+  return -1;
+}
+
+const txXPathNode& txNodeSet::get(int32_t aIndex) const {
+  if (mDirection == kForward) {
+    return mStart[aIndex];
+  }
+
+  return mEnd[-aIndex - 1];
+}
+
+short txNodeSet::getResultType() { return txAExprResult::NODESET; }
+
+bool txNodeSet::booleanValue() { return !isEmpty(); }
+double txNodeSet::numberValue() {
+  nsAutoString str;
+  stringValue(str);
+
+  return txDouble::toDouble(str);
+}
+
+void txNodeSet::stringValue(nsString& aStr) {
+  NS_ASSERTION(mDirection == kForward,
+               "only append(aNode) is supported on reversed nodesets");
+  if (isEmpty()) {
+    return;
+  }
+  txXPathNodeUtils::appendNodeValue(get(0), aStr);
+}
+
+const nsString* txNodeSet::stringValuePointer() { return nullptr; }
+
+bool txNodeSet::ensureGrowSize(int32_t aSize) {
+  // check if there is enough place in the buffer as is
+  if (mDirection == kForward && aSize <= mEndBuffer - mEnd) {
+    return true;
+  }
+
+  if (mDirection == kReversed && aSize <= mStart - mStartBuffer) {
+    return true;
+  }
+
+  // check if we just have to align mStart to have enough space
+  int32_t oldSize = mEnd - mStart;
+  int32_t oldLength = mEndBuffer - mStartBuffer;
+  int32_t ensureSize = oldSize + aSize;
+  if (ensureSize <= oldLength) {
+    // just move the buffer
+    txXPathNode* dest = mStartBuffer;
+    if (mDirection == kReversed) {
+      dest = mEndBuffer - oldSize;
+    }
+    LOG_CHUNK_MOVE(mStart, dest, oldSize);
+    memmove(dest, mStart, oldSize * sizeof(txXPathNode));
+    mStart = dest;
+    mEnd = dest + oldSize;
+
+    return true;
+  }
+
+  // This isn't 100% safe. But until someone manages to make a 1gig nodeset
+  // it should be ok.
+  int32_t newLength = std::max(oldLength, kTxNodeSetMinSize);
+
+  while (newLength < ensureSize) {
+    newLength *= kTxNodeSetGrowFactor;
+  }
+
+  txXPathNode* newArr =
+      static_cast<txXPathNode*>(moz_xmalloc(newLength * sizeof(txXPathNode)));
+
+  txXPathNode* dest = newArr;
+  if (mDirection == kReversed) {
+    dest += newLength - oldSize;
+  }
+
+  if (oldSize > 0) {
+    LOG_CHUNK_MOVE(mStart, dest, oldSize);
+    memcpy(dest, mStart, oldSize * sizeof(txXPathNode));
+  }
+
+  if (mStartBuffer) {
+#ifdef DEBUG
+    memset(mStartBuffer, 0, (mEndBuffer - mStartBuffer) * sizeof(txXPathNode));
+#endif
+    free(mStartBuffer);
+  }
+
+  mStartBuffer = newArr;
+  mEndBuffer = mStartBuffer + newLength;
+  mStart = dest;
+  mEnd = dest + oldSize;
+
+  return true;
+}
+
+txXPathNode* txNodeSet::findPosition(const txXPathNode& aNode,
+                                     txXPathNode* aFirst, txXPathNode* aLast,
+                                     bool& aDupe) const {
+  aDupe = false;
+  if (aLast - aFirst <= 2) {
+    // If we search 2 nodes or less there is no point in further divides
+    txXPathNode* pos = aFirst;
+    for (; pos < aLast; ++pos) {
+      int cmp = txXPathNodeUtils::comparePosition(aNode, *pos);
+      if (cmp < 0) {
+        return pos;
+      }
+
+      if (cmp == 0) {
+        aDupe = true;
+
+        return pos;
+      }
+    }
+    return pos;
+  }
+
+  // (cannot add two pointers)
+  txXPathNode* midpos = aFirst + (aLast - aFirst) / 2;
+  int cmp = txXPathNodeUtils::comparePosition(aNode, *midpos);
+  if (cmp == 0) {
+    aDupe = true;
+
+    return midpos;
+  }
+
+  if (cmp > 0) {
+    return findPosition(aNode, midpos + 1, aLast, aDupe);
+  }
+
+  // midpos excluded as end of range
+
+  return findPosition(aNode, aFirst, midpos, aDupe);
+}
+
+/* static */
+void txNodeSet::copyElements(txXPathNode* aDest, const txXPathNode* aStart,
+                             const txXPathNode* aEnd) {
+  const txXPathNode* pos = aStart;
+  while (pos < aEnd) {
+    new (aDest) txXPathNode(*pos);
+    ++aDest;
+    ++pos;
+  }
+}
+
+/* static */
+void txNodeSet::transferElements(txXPathNode* aDest, const txXPathNode* aStart,
+                                 const txXPathNode* aEnd) {
+  LOG_CHUNK_MOVE(aStart, aDest, (aEnd - aStart));
+  memcpy(aDest, aStart, (aEnd - aStart) * sizeof(txXPathNode));
+}
diff --git a/dom/xslt/xpath/txNodeSet.h b/dom/xslt/xpath/txNodeSet.h
new file mode 100644
index 0000000000..8c5e805d6b
--- /dev/null
+++ b/dom/xslt/xpath/txNodeSet.h
@@ -0,0 +1,199 @@
+/* -*- Mode: C++; tab-width: 4; 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/. */
+
+/**
+ * Implementation of an XPath NodeSet
+ */
+
+#ifndef txNodeSet_h__
+#define txNodeSet_h__
+
+#include "txExprResult.h"
+#include "nsError.h"
+#include "txXPathNode.h"
+
+class txNodeSet : public txAExprResult {
+ public:
+  /**
+   * Creates a new empty NodeSet
+   */
+  explicit txNodeSet(txResultRecycler* aRecycler);
+
+  /**
+   * Creates a new NodeSet with one node.
+   */
+  txNodeSet(const txXPathNode& aNode, txResultRecycler* aRecycler);
+
+  /**
+   * Creates a new txNodeSet, copying the node references from the source
+   * NodeSet.
+   */
+  txNodeSet(const txNodeSet& aSource, txResultRecycler* aRecycler);
+
+  /**
+   * Destructor for txNodeSet, deletes the nodes.
+   */
+  virtual ~txNodeSet();
+
+  /**
+   * Adds the specified txXPathNode to this NodeSet if it is not already
+   * in this NodeSet. The node is inserted according to document order.
+   *
+   * @param  aNode the txXPathNode to add to the NodeSet
+   * @return errorcode.
+   */
+  nsresult add(const txXPathNode& aNode);
+
+  /**
+   * Adds the nodes in specified NodeSet to this NodeSet. The resulting
+   * NodeSet is sorted in document order and does not contain any duplicate
+   * nodes.
+   *
+   * @param  aNodes the NodeSet to add, must be in document order.
+   * @return errorcode.
+   */
+  nsresult add(const txNodeSet& aNodes);
+  nsresult addAndTransfer(txNodeSet* aNodes);
+
+  /**
+   * Append API
+   * These functions should be used with care.
+   * They are intended to be used when the caller assures that the resulting
+   * NodeSet remains in document order.
+   * Abuse will break document order, and cause errors in the result.
+   * These functions are significantly faster than the add API, as no
+   * order info operations will be performed.
+   */
+
+  /**
+   * Appends the specified Node to the end of this NodeSet
+   * @param  aNode the Node to append to the NodeSet
+   * @return errorcode.
+   */
+  nsresult append(const txXPathNode& aNode);
+
+  /**
+   * Appends the nodes in the specified NodeSet to the end of this NodeSet
+   * @param  aNodes the NodeSet to append to the NodeSet
+   * @return errorcode.
+   */
+  nsresult append(const txNodeSet& aNodes);
+
+  /**
+   * API to implement reverse axes in LocationStep.
+   *
+   * Before adding nodes to the nodeset for a reversed axis, call
+   * setReverse(). This will make the append(aNode) and get() methods treat
+   * the nodeset as required. Do only call append(aNode), get(), mark()
+   * and sweep() while the nodeset is reversed.
+   * Afterwards, call unsetReverse(). The nodes are stored in document
+   * order internally.
+   */
+  void setReverse() { mDirection = -1; }
+  void unsetReverse() { mDirection = 1; }
+
+  /**
+   * API to implement predicates in PredicateExpr
+   *
+   * mark(aIndex) marks the specified member of the nodeset.
+   * sweep() clears all members of the nodeset that haven't been
+   * marked before and clear the mMarks array.
+   */
+  nsresult mark(int32_t aIndex);
+  nsresult sweep();
+
+  /**
+   * Removes all nodes from this nodeset
+   */
+  void clear();
+
+  /**
+   * Returns the index of the specified Node,
+   * or -1 if the Node is not contained in the NodeSet
+   * @param  aNode the Node to get the index for
+   * @param  aStart index to start searching at
+   * @return index of specified node or -1 if the node does not exist
+   */
+  int32_t indexOf(const txXPathNode& aNode, uint32_t aStart = 0) const;
+
+  /**
+   * Returns true if the specified Node is contained in the set.
+   * @param  aNode the Node to search for
+   * @return true if specified Node is contained in the NodeSet
+   */
+  bool contains(const txXPathNode& aNode) const { return indexOf(aNode) >= 0; }
+
+  /**
+   * Returns the Node at the specified node in this NodeSet.
+   * @param  aIndex the node of the Node to return
+   * @return Node at specified node
+   */
+  const txXPathNode& get(int32_t aIndex) const;
+
+  /**
+   * Returns true if there are no Nodes in the NodeSet.
+   * @return true if there are no Nodes in the NodeSet.
+   */
+  bool isEmpty() const { return mStart ? mStart == mEnd : true; }
+
+  /**
+   * Returns the number of elements in the NodeSet
+   * @return the number of elements in the NodeSet
+   */
+  int32_t size() const { return mStart ? mEnd - mStart : 0; }
+
+  TX_DECL_EXPRRESULT
+
+ private:
+  /**
+   * Ensure that this nodeset can take another aSize nodes.
+   *
+   * Changes mStart and mEnd as well as mBufferStart and mBufferEnd.
+   */
+  bool ensureGrowSize(int32_t aSize);
+
+  /**
+   * Finds position in the buffer where a node should be inserted
+   * to keep the nodeset in document order. Searches the positions
+   * aFirst-aLast, including aFirst, but not aLast.
+   * @param  aNode   Node to find insert position for.
+   * @param  aFirst  First item of the search range, included.
+   * @param  aLast   Last item of the search range, excluded.
+   * @param  aDupe   out-param. Will be set to true if the node already
+   *                 exists in the NodeSet, false if it should be
+   *                 inserted.
+   * @return pointer where to insert the node. The node should be inserted
+   *         before the given node. This value is always set, even if aNode
+   *         already exists in the NodeSet
+   */
+  txXPathNode* findPosition(const txXPathNode& aNode, txXPathNode* aFirst,
+                            txXPathNode* aLast, bool& aDupe) const;
+
+  static void copyElements(txXPathNode* aDest, const txXPathNode* aStart,
+                           const txXPathNode* aEnd);
+  static void transferElements(txXPathNode* aDest, const txXPathNode* aStart,
+                               const txXPathNode* aEnd);
+  static void destroyElements(const txXPathNode* aStart,
+                              const txXPathNode* aEnd) {
+    while (aStart < aEnd) {
+      aStart->~txXPathNode();
+      ++aStart;
+    }
+  }
+
+  using transferOp = void (*)(txXPathNode* aDest, const txXPathNode* aStart,
+                              const txXPathNode* aEnd);
+  using destroyOp = void (*)(const txXPathNode* aStart,
+                             const txXPathNode* aEnd);
+  nsresult add(const txNodeSet& aNodes, transferOp aTransfer,
+               destroyOp aDestroy);
+
+  txXPathNode *mStart, *mEnd, *mStartBuffer, *mEndBuffer;
+  int32_t mDirection;
+  // used for mark() and sweep() in predicates
+  bool* mMarks;
+};
+
+#endif
diff --git a/dom/xslt/xpath/txNodeSetContext.cpp b/dom/xslt/xpath/txNodeSetContext.cpp
new file mode 100644
index 0000000000..7565e12545
--- /dev/null
+++ b/dom/xslt/xpath/txNodeSetContext.cpp
@@ -0,0 +1,51 @@
+/* -*- Mode: C++; tab-width: 4; 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/. */
+
+#include "txNodeSetContext.h"
+#include "txNodeSet.h"
+
+const txXPathNode& txNodeSetContext::getContextNode() {
+  return mContextSet->get(mPosition - 1);
+}
+
+uint32_t txNodeSetContext::size() { return (uint32_t)mContextSet->size(); }
+
+uint32_t txNodeSetContext::position() {
+  NS_ASSERTION(mPosition, "Should have called next() at least once");
+  return mPosition;
+}
+
+nsresult txNodeSetContext::getVariable(int32_t aNamespace, nsAtom* aLName,
+                                       txAExprResult*& aResult) {
+  NS_ASSERTION(mInner, "mInner is null!!!");
+  return mInner->getVariable(aNamespace, aLName, aResult);
+}
+
+nsresult txNodeSetContext::isStripSpaceAllowed(const txXPathNode& aNode,
+                                               bool& aAllowed) {
+  NS_ASSERTION(mInner, "mInner is null!!!");
+  return mInner->isStripSpaceAllowed(aNode, aAllowed);
+}
+
+void* txNodeSetContext::getPrivateContext() {
+  NS_ASSERTION(mInner, "mInner is null!!!");
+  return mInner->getPrivateContext();
+}
+
+txResultRecycler* txNodeSetContext::recycler() {
+  NS_ASSERTION(mInner, "mInner is null!!!");
+  return mInner->recycler();
+}
+
+void txNodeSetContext::receiveError(const nsAString& aMsg, nsresult aRes) {
+  NS_ASSERTION(mInner, "mInner is null!!!");
+#ifdef DEBUG
+  nsAutoString error(u"forwarded error: "_ns);
+  error.Append(aMsg);
+  mInner->receiveError(error, aRes);
+#else
+  mInner->receiveError(aMsg, aRes);
+#endif
+}
diff --git a/dom/xslt/xpath/txNodeSetContext.h b/dom/xslt/xpath/txNodeSetContext.h
new file mode 100644
index 0000000000..86cb14ab95
--- /dev/null
+++ b/dom/xslt/xpath/txNodeSetContext.h
@@ -0,0 +1,36 @@
+/* -*- Mode: C++; tab-width: 4; 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 __TX_XPATH_SET_CONTEXT
+#define __TX_XPATH_SET_CONTEXT
+
+#include "txIXPathContext.h"
+#include "txNodeSet.h"
+
+class txNodeSetContext : public txIEvalContext {
+ public:
+  txNodeSetContext(txNodeSet* aContextNodeSet, txIMatchContext* aContext)
+      : mContextSet(aContextNodeSet), mPosition(0), mInner(aContext) {}
+
+  // Iteration over the given NodeSet
+  bool hasNext() { return mPosition < size(); }
+  void next() {
+    NS_ASSERTION(mPosition < size(), "Out of bounds.");
+    mPosition++;
+  }
+  void setPosition(uint32_t aPosition) {
+    NS_ASSERTION(aPosition > 0 && aPosition <= size(), "Out of bounds.");
+    mPosition = aPosition;
+  }
+
+  TX_DECL_EVAL_CONTEXT;
+
+ protected:
+  RefPtr<txNodeSet> mContextSet;
+  uint32_t mPosition;
+  txIMatchContext* mInner;
+};
+
+#endif  // __TX_XPATH_SET_CONTEXT
diff --git a/dom/xslt/xpath/txNodeTypeTest.cpp b/dom/xslt/xpath/txNodeTypeTest.cpp
new file mode 100644
index 0000000000..17d0c60483
--- /dev/null
+++ b/dom/xslt/xpath/txNodeTypeTest.cpp
@@ -0,0 +1,91 @@
+/* -*- Mode: C++; tab-width: 4; 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/. */
+
+#include "txExpr.h"
+#include "nsAtom.h"
+#include "txIXPathContext.h"
+#include "txXPathTreeWalker.h"
+
+nsresult txNodeTypeTest::matches(const txXPathNode& aNode,
+                                 txIMatchContext* aContext, bool& aMatched) {
+  switch (mNodeType) {
+    case COMMENT_TYPE: {
+      aMatched = txXPathNodeUtils::isComment(aNode);
+      return NS_OK;
+    }
+    case TEXT_TYPE: {
+      aMatched = txXPathNodeUtils::isText(aNode);
+      if (aMatched) {
+        bool allowed;
+        nsresult rv = aContext->isStripSpaceAllowed(aNode, allowed);
+        NS_ENSURE_SUCCESS(rv, rv);
+
+        aMatched = !allowed;
+      }
+      return NS_OK;
+    }
+    case PI_TYPE: {
+      aMatched =
+          txXPathNodeUtils::isProcessingInstruction(aNode) &&
+          (!mNodeName || txXPathNodeUtils::localNameEquals(aNode, mNodeName));
+      return NS_OK;
+    }
+    case NODE_TYPE: {
+      if (txXPathNodeUtils::isText(aNode)) {
+        bool allowed;
+        nsresult rv = aContext->isStripSpaceAllowed(aNode, allowed);
+        NS_ENSURE_SUCCESS(rv, rv);
+
+        aMatched = !allowed;
+      } else {
+        aMatched = true;
+      }
+      return NS_OK;
+    }
+  }
+
+  MOZ_ASSERT_UNREACHABLE("Didn't deal with all values of the NodeType enum!");
+
+  aMatched = false;
+  return NS_OK;
+}
+
+txNodeTest::NodeTestType txNodeTypeTest::getType() { return NODETYPE_TEST; }
+
+/*
+ * Returns the default priority of this txNodeTest
+ */
+double txNodeTypeTest::getDefaultPriority() { return mNodeName ? 0 : -0.5; }
+
+bool txNodeTypeTest::isSensitiveTo(Expr::ContextSensitivity aContext) {
+  return !!(aContext & Expr::NODE_CONTEXT);
+}
+
+#ifdef TX_TO_STRING
+void txNodeTypeTest::toString(nsAString& aDest) {
+  switch (mNodeType) {
+    case COMMENT_TYPE:
+      aDest.AppendLiteral("comment()");
+      break;
+    case TEXT_TYPE:
+      aDest.AppendLiteral("text()");
+      break;
+    case PI_TYPE:
+      aDest.AppendLiteral("processing-instruction(");
+      if (mNodeName) {
+        nsAutoString str;
+        mNodeName->ToString(str);
+        aDest.Append(char16_t('\''));
+        aDest.Append(str);
+        aDest.Append(char16_t('\''));
+      }
+      aDest.Append(char16_t(')'));
+      break;
+    case NODE_TYPE:
+      aDest.AppendLiteral("node()");
+      break;
+  }
+}
+#endif
diff --git a/dom/xslt/xpath/txNumberExpr.cpp b/dom/xslt/xpath/txNumberExpr.cpp
new file mode 100644
index 0000000000..c3424a91f1
--- /dev/null
+++ b/dom/xslt/xpath/txNumberExpr.cpp
@@ -0,0 +1,108 @@
+/* -*- Mode: C++; tab-width: 4; 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/. */
+
+#include "mozilla/FloatingPoint.h"
+
+#include "txExpr.h"
+#include <math.h>
+#include "txIXPathContext.h"
+
+nsresult txNumberExpr::evaluate(txIEvalContext* aContext,
+                                txAExprResult** aResult) {
+  *aResult = nullptr;
+
+  RefPtr<txAExprResult> exprRes;
+  nsresult rv = mRightExpr->evaluate(aContext, getter_AddRefs(exprRes));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  double rightDbl = exprRes->numberValue();
+
+  rv = mLeftExpr->evaluate(aContext, getter_AddRefs(exprRes));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  double leftDbl = exprRes->numberValue();
+  double result = 0;
+
+  switch (mOp) {
+    case ADD:
+      result = leftDbl + rightDbl;
+      break;
+
+    case SUBTRACT:
+      result = leftDbl - rightDbl;
+      break;
+
+    case DIVIDE:
+      if (rightDbl == 0) {
+#if defined(XP_WIN)
+        /* XXX MSVC miscompiles such that (NaN == 0) */
+        if (std::isnan(rightDbl))
+          result = mozilla::UnspecifiedNaN<double>();
+        else
+#endif
+            if (leftDbl == 0 || std::isnan(leftDbl))
+          result = mozilla::UnspecifiedNaN<double>();
+        else if (mozilla::IsNegative(leftDbl) != mozilla::IsNegative(rightDbl))
+          result = mozilla::NegativeInfinity<double>();
+        else
+          result = mozilla::PositiveInfinity<double>();
+      } else
+        result = leftDbl / rightDbl;
+      break;
+
+    case MODULUS:
+      if (rightDbl == 0) {
+        result = mozilla::UnspecifiedNaN<double>();
+      } else {
+#if defined(XP_WIN)
+        /* Workaround MS fmod bug where 42 % (1/0) => NaN, not 42. */
+        if (!std::isinf(leftDbl) && std::isinf(rightDbl))
+          result = leftDbl;
+        else
+#endif
+          result = fmod(leftDbl, rightDbl);
+      }
+      break;
+
+    case MULTIPLY:
+      result = leftDbl * rightDbl;
+      break;
+  }
+
+  return aContext->recycler()->getNumberResult(result, aResult);
+}  //-- evaluate
+
+TX_IMPL_EXPR_STUBS_2(txNumberExpr, NUMBER_RESULT, mLeftExpr, mRightExpr)
+
+bool txNumberExpr::isSensitiveTo(ContextSensitivity aContext) {
+  return mLeftExpr->isSensitiveTo(aContext) ||
+         mRightExpr->isSensitiveTo(aContext);
+}
+
+#ifdef TX_TO_STRING
+void txNumberExpr::toString(nsAString& str) {
+  mLeftExpr->toString(str);
+
+  switch (mOp) {
+    case ADD:
+      str.AppendLiteral(" + ");
+      break;
+    case SUBTRACT:
+      str.AppendLiteral(" - ");
+      break;
+    case DIVIDE:
+      str.AppendLiteral(" div ");
+      break;
+    case MODULUS:
+      str.AppendLiteral(" mod ");
+      break;
+    case MULTIPLY:
+      str.AppendLiteral(" * ");
+      break;
+  }
+
+  mRightExpr->toString(str);
+}
+#endif
diff --git a/dom/xslt/xpath/txNumberResult.cpp b/dom/xslt/xpath/txNumberResult.cpp
new file mode 100644
index 0000000000..370a7523d8
--- /dev/null
+++ b/dom/xslt/xpath/txNumberResult.cpp
@@ -0,0 +1,48 @@
+/* -*- Mode: C++; tab-width: 4; 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/. */
+
+/**
+ * NumberResult
+ * Represents the a number as the result of evaluating an Expr
+ **/
+
+#include "mozilla/FloatingPoint.h"
+
+#include "txExprResult.h"
+
+/**
+ * Default Constructor
+ **/
+
+/**
+ * Creates a new NumberResult with the value of the given double parameter
+ * @param dbl the double to use for initialization of this NumberResult's value
+ **/
+NumberResult::NumberResult(double aValue, txResultRecycler* aRecycler)
+    : txAExprResult(aRecycler), value(aValue) {}  //-- NumberResult
+
+/*
+ * Virtual Methods from ExprResult
+ */
+
+short NumberResult::getResultType() {
+  return txAExprResult::NUMBER;
+}  //-- getResultType
+
+void NumberResult::stringValue(nsString& aResult) {
+  txDouble::toString(value, aResult);
+}
+
+const nsString* NumberResult::stringValuePointer() { return nullptr; }
+
+bool NumberResult::booleanValue() {
+  // OG+
+  // As per the XPath spec, the boolean value of a number is true if and only if
+  // it is neither positive 0 nor negative 0 nor NaN
+  return (bool)(value != 0.0 && !std::isnan(value));
+  // OG-
+}  //-- booleanValue
+
+double NumberResult::numberValue() { return this->value; }  //-- numberValue
diff --git a/dom/xslt/xpath/txPathExpr.cpp b/dom/xslt/xpath/txPathExpr.cpp
new file mode 100644
index 0000000000..79be4caa08
--- /dev/null
+++ b/dom/xslt/xpath/txPathExpr.cpp
@@ -0,0 +1,229 @@
+/* -*- Mode: C++; tab-width: 4; 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/. */
+
+#include "txExpr.h"
+#include "txNodeSet.h"
+#include "txNodeSetContext.h"
+#include "txSingleNodeContext.h"
+#include "txXMLUtils.h"
+#include "txXPathTreeWalker.h"
+
+using mozilla::Unused;
+using mozilla::WrapUnique;
+
+//------------/
+//- PathExpr -/
+//------------/
+
+/**
+ * Adds the Expr to this PathExpr
+ * @param expr the Expr to add to this PathExpr
+ **/
+void PathExpr::addExpr(Expr* aExpr, PathOperator aPathOp) {
+  NS_ASSERTION(!mItems.IsEmpty() || aPathOp == RELATIVE_OP,
+               "First step has to be relative in PathExpr");
+  PathExprItem* pxi = mItems.AppendElement();
+  pxi->expr = WrapUnique(aExpr);
+  pxi->pathOp = aPathOp;
+}
+
+//-----------------------------/
+//- Virtual methods from Expr -/
+//-----------------------------/
+
+/**
+ * Evaluates this Expr based on the given context node and processor state
+ * @param context the context node for evaluation of this Expr
+ * @param ps the ContextState containing the stack information needed
+ * for evaluation
+ * @return the result of the evaluation
+ **/
+nsresult PathExpr::evaluate(txIEvalContext* aContext, txAExprResult** aResult) {
+  *aResult = nullptr;
+
+  // We need to evaluate the first step with the current context since it
+  // can depend on the context size and position. For example:
+  // key('books', concat('book', position()))
+  RefPtr<txAExprResult> res;
+  nsresult rv = mItems[0].expr->evaluate(aContext, getter_AddRefs(res));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  NS_ENSURE_TRUE(res->getResultType() == txAExprResult::NODESET,
+                 NS_ERROR_XSLT_NODESET_EXPECTED);
+
+  RefPtr<txNodeSet> nodes =
+      static_cast<txNodeSet*>(static_cast<txAExprResult*>(res));
+  if (nodes->isEmpty()) {
+    res.forget(aResult);
+
+    return NS_OK;
+  }
+  res = nullptr;  // To allow recycling
+
+  // Evaluate remaining steps
+  uint32_t i, len = mItems.Length();
+  for (i = 1; i < len; ++i) {
+    PathExprItem& pxi = mItems[i];
+    RefPtr<txNodeSet> tmpNodes;
+    txNodeSetContext eContext(nodes, aContext);
+    while (eContext.hasNext()) {
+      eContext.next();
+
+      RefPtr<txNodeSet> resNodes;
+      if (pxi.pathOp == DESCENDANT_OP) {
+        rv = aContext->recycler()->getNodeSet(getter_AddRefs(resNodes));
+        NS_ENSURE_SUCCESS(rv, rv);
+
+        rv = evalDescendants(pxi.expr.get(), eContext.getContextNode(),
+                             &eContext, resNodes);
+        NS_ENSURE_SUCCESS(rv, rv);
+      } else {
+        RefPtr<txAExprResult> res;
+        rv = pxi.expr->evaluate(&eContext, getter_AddRefs(res));
+        NS_ENSURE_SUCCESS(rv, rv);
+
+        if (res->getResultType() != txAExprResult::NODESET) {
+          // XXX ErrorReport: report nonnodeset error
+          return NS_ERROR_XSLT_NODESET_EXPECTED;
+        }
+        resNodes = static_cast<txNodeSet*>(static_cast<txAExprResult*>(res));
+      }
+
+      if (tmpNodes) {
+        if (!resNodes->isEmpty()) {
+          RefPtr<txNodeSet> oldSet;
+          oldSet.swap(tmpNodes);
+          rv = aContext->recycler()->getNonSharedNodeSet(
+              oldSet, getter_AddRefs(tmpNodes));
+          NS_ENSURE_SUCCESS(rv, rv);
+
+          oldSet.swap(resNodes);
+          rv = aContext->recycler()->getNonSharedNodeSet(
+              oldSet, getter_AddRefs(resNodes));
+          NS_ENSURE_SUCCESS(rv, rv);
+
+          tmpNodes->addAndTransfer(resNodes);
+        }
+      } else {
+        tmpNodes = resNodes;
+      }
+    }
+    nodes = tmpNodes;
+    if (nodes->isEmpty()) {
+      break;
+    }
+  }
+
+  *aResult = nodes;
+  NS_ADDREF(*aResult);
+
+  return NS_OK;
+}  //-- evaluate
+
+/**
+ * Selects from the descendants of the context node
+ * all nodes that match the Expr
+ **/
+nsresult PathExpr::evalDescendants(Expr* aStep, const txXPathNode& aNode,
+                                   txIMatchContext* aContext,
+                                   txNodeSet* resNodes) {
+  txSingleNodeContext eContext(aNode, aContext);
+  RefPtr<txAExprResult> res;
+  nsresult rv = aStep->evaluate(&eContext, getter_AddRefs(res));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  if (res->getResultType() != txAExprResult::NODESET) {
+    // XXX ErrorReport: report nonnodeset error
+    return NS_ERROR_XSLT_NODESET_EXPECTED;
+  }
+
+  txNodeSet* oldSet = static_cast<txNodeSet*>(static_cast<txAExprResult*>(res));
+  RefPtr<txNodeSet> newSet;
+  rv =
+      aContext->recycler()->getNonSharedNodeSet(oldSet, getter_AddRefs(newSet));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  resNodes->addAndTransfer(newSet);
+
+  bool filterWS;
+  rv = aContext->isStripSpaceAllowed(aNode, filterWS);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  txXPathTreeWalker walker(aNode);
+  if (!walker.moveToFirstChild()) {
+    return NS_OK;
+  }
+
+  do {
+    const txXPathNode& node = walker.getCurrentPosition();
+    if (!(filterWS && txXPathNodeUtils::isText(node) &&
+          txXPathNodeUtils::isWhitespace(node))) {
+      rv = evalDescendants(aStep, node, aContext, resNodes);
+      NS_ENSURE_SUCCESS(rv, rv);
+    }
+  } while (walker.moveToNextSibling());
+
+  return NS_OK;
+}  //-- evalDescendants
+
+Expr::ExprType PathExpr::getType() { return PATH_EXPR; }
+
+TX_IMPL_EXPR_STUBS_BASE(PathExpr, NODESET_RESULT)
+
+Expr* PathExpr::getSubExprAt(uint32_t aPos) {
+  return aPos < mItems.Length() ? mItems[aPos].expr.get() : nullptr;
+}
+void PathExpr::setSubExprAt(uint32_t aPos, Expr* aExpr) {
+  NS_ASSERTION(aPos < mItems.Length(), "setting bad subexpression index");
+  Unused << mItems[aPos].expr.release();
+  mItems[aPos].expr = WrapUnique(aExpr);
+}
+
+bool PathExpr::isSensitiveTo(ContextSensitivity aContext) {
+  if (mItems[0].expr->isSensitiveTo(aContext)) {
+    return true;
+  }
+
+  // We're creating a new node/nodeset so we can ignore those bits.
+  Expr::ContextSensitivity context =
+      aContext & ~(Expr::NODE_CONTEXT | Expr::NODESET_CONTEXT);
+  if (context == NO_CONTEXT) {
+    return false;
+  }
+
+  uint32_t i, len = mItems.Length();
+  for (i = 0; i < len; ++i) {
+    NS_ASSERTION(!mItems[i].expr->isSensitiveTo(Expr::NODESET_CONTEXT),
+                 "Step cannot depend on nodeset-context");
+    if (mItems[i].expr->isSensitiveTo(context)) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+#ifdef TX_TO_STRING
+void PathExpr::toString(nsAString& dest) {
+  if (!mItems.IsEmpty()) {
+    NS_ASSERTION(mItems[0].pathOp == RELATIVE_OP,
+                 "First step should be relative");
+    mItems[0].expr->toString(dest);
+  }
+
+  uint32_t i, len = mItems.Length();
+  for (i = 1; i < len; ++i) {
+    switch (mItems[i].pathOp) {
+      case DESCENDANT_OP:
+        dest.AppendLiteral("//");
+        break;
+      case RELATIVE_OP:
+        dest.Append(char16_t('/'));
+        break;
+    }
+    mItems[i].expr->toString(dest);
+  }
+}
+#endif
diff --git a/dom/xslt/xpath/txPredicateList.cpp b/dom/xslt/xpath/txPredicateList.cpp
new file mode 100644
index 0000000000..ad2804caef
--- /dev/null
+++ b/dom/xslt/xpath/txPredicateList.cpp
@@ -0,0 +1,78 @@
+/* -*- Mode: C++; tab-width: 4; 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/. */
+
+#include "txExpr.h"
+#include "txNodeSet.h"
+#include "txNodeSetContext.h"
+
+/*
+ * Represents an ordered list of Predicates,
+ * for use with Step and Filter Expressions
+ */
+
+nsresult PredicateList::evaluatePredicates(txNodeSet* nodes,
+                                           txIMatchContext* aContext) {
+  NS_ASSERTION(nodes, "called evaluatePredicates with nullptr NodeSet");
+  nsresult rv = NS_OK;
+
+  uint32_t i, len = mPredicates.Length();
+  for (i = 0; i < len && !nodes->isEmpty(); ++i) {
+    txNodeSetContext predContext(nodes, aContext);
+    /*
+     * add nodes to newNodes that match the expression
+     * or, if the result is a number, add the node with the right
+     * position
+     */
+    int32_t index = 0;
+    while (predContext.hasNext()) {
+      predContext.next();
+      RefPtr<txAExprResult> exprResult;
+      rv = mPredicates[i]->evaluate(&predContext, getter_AddRefs(exprResult));
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      // handle default, [position() == numberValue()]
+      if (exprResult->getResultType() == txAExprResult::NUMBER) {
+        if ((double)predContext.position() == exprResult->numberValue()) {
+          nodes->mark(index);
+        }
+      } else if (exprResult->booleanValue()) {
+        nodes->mark(index);
+      }
+      ++index;
+    }
+    // sweep the non-marked nodes
+    nodes->sweep();
+  }
+
+  return NS_OK;
+}
+
+bool PredicateList::isSensitiveTo(Expr::ContextSensitivity aContext) {
+  // We're creating a new node/nodeset so we can ignore those bits.
+  Expr::ContextSensitivity context =
+      aContext & ~(Expr::NODE_CONTEXT | Expr::NODESET_CONTEXT);
+  if (context == Expr::NO_CONTEXT) {
+    return false;
+  }
+
+  uint32_t i, len = mPredicates.Length();
+  for (i = 0; i < len; ++i) {
+    if (mPredicates[i]->isSensitiveTo(context)) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+#ifdef TX_TO_STRING
+void PredicateList::toString(nsAString& dest) {
+  for (uint32_t i = 0; i < mPredicates.Length(); ++i) {
+    dest.Append(char16_t('['));
+    mPredicates[i]->toString(dest);
+    dest.Append(char16_t(']'));
+  }
+}
+#endif
diff --git a/dom/xslt/xpath/txPredicatedNodeTest.cpp b/dom/xslt/xpath/txPredicatedNodeTest.cpp
new file mode 100644
index 0000000000..6c3fd33cf5
--- /dev/null
+++ b/dom/xslt/xpath/txPredicatedNodeTest.cpp
@@ -0,0 +1,50 @@
+/* -*- Mode: C++; tab-width: 4; 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/. */
+
+#include "txExpr.h"
+#include "txExprResult.h"
+#include "txSingleNodeContext.h"
+
+txPredicatedNodeTest::txPredicatedNodeTest(txNodeTest* aNodeTest,
+                                           Expr* aPredicate)
+    : mNodeTest(aNodeTest), mPredicate(aPredicate) {
+  NS_ASSERTION(!mPredicate->isSensitiveTo(Expr::NODESET_CONTEXT),
+               "predicate must not be context-nodeset-sensitive");
+}
+
+nsresult txPredicatedNodeTest::matches(const txXPathNode& aNode,
+                                       txIMatchContext* aContext,
+                                       bool& aMatched) {
+  nsresult rv = mNodeTest->matches(aNode, aContext, aMatched);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  if (!aMatched) {
+    return NS_OK;
+  }
+
+  txSingleNodeContext context(aNode, aContext);
+  RefPtr<txAExprResult> res;
+  rv = mPredicate->evaluate(&context, getter_AddRefs(res));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  aMatched = res->booleanValue();
+  return NS_OK;
+}
+
+double txPredicatedNodeTest::getDefaultPriority() { return 0.5; }
+
+bool txPredicatedNodeTest::isSensitiveTo(Expr::ContextSensitivity aContext) {
+  return mNodeTest->isSensitiveTo(aContext) ||
+         mPredicate->isSensitiveTo(aContext);
+}
+
+#ifdef TX_TO_STRING
+void txPredicatedNodeTest::toString(nsAString& aDest) {
+  mNodeTest->toString(aDest);
+  aDest.Append(char16_t('['));
+  mPredicate->toString(aDest);
+  aDest.Append(char16_t(']'));
+}
+#endif
diff --git a/dom/xslt/xpath/txRelationalExpr.cpp b/dom/xslt/xpath/txRelationalExpr.cpp
new file mode 100644
index 0000000000..df6da87ca8
--- /dev/null
+++ b/dom/xslt/xpath/txRelationalExpr.cpp
@@ -0,0 +1,184 @@
+/* -*- Mode: C++; tab-width: 4; 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/. */
+
+#include "txExpr.h"
+#include "txNodeSet.h"
+#include "txIXPathContext.h"
+#include "txXPathTreeWalker.h"
+
+/**
+ *  Compares the two ExprResults based on XPath 1.0 Recommendation (section 3.4)
+ */
+bool RelationalExpr::compareResults(txIEvalContext* aContext,
+                                    txAExprResult* aLeft,
+                                    txAExprResult* aRight) {
+  short ltype = aLeft->getResultType();
+  short rtype = aRight->getResultType();
+  nsresult rv = NS_OK;
+
+  // Handle case for just Left NodeSet or Both NodeSets
+  if (ltype == txAExprResult::NODESET) {
+    if (rtype == txAExprResult::BOOLEAN) {
+      BooleanResult leftBool(aLeft->booleanValue());
+      return compareResults(aContext, &leftBool, aRight);
+    }
+
+    txNodeSet* nodeSet = static_cast<txNodeSet*>(aLeft);
+    RefPtr<StringResult> strResult;
+    rv = aContext->recycler()->getStringResult(getter_AddRefs(strResult));
+    NS_ENSURE_SUCCESS(rv, false);
+
+    int32_t i;
+    for (i = 0; i < nodeSet->size(); ++i) {
+      strResult->mValue.Truncate();
+      txXPathNodeUtils::appendNodeValue(nodeSet->get(i), strResult->mValue);
+      if (compareResults(aContext, strResult, aRight)) {
+        return true;
+      }
+    }
+
+    return false;
+  }
+
+  // Handle case for Just Right NodeSet
+  if (rtype == txAExprResult::NODESET) {
+    if (ltype == txAExprResult::BOOLEAN) {
+      BooleanResult rightBool(aRight->booleanValue());
+      return compareResults(aContext, aLeft, &rightBool);
+    }
+
+    txNodeSet* nodeSet = static_cast<txNodeSet*>(aRight);
+    RefPtr<StringResult> strResult;
+    rv = aContext->recycler()->getStringResult(getter_AddRefs(strResult));
+    NS_ENSURE_SUCCESS(rv, false);
+
+    int32_t i;
+    for (i = 0; i < nodeSet->size(); ++i) {
+      strResult->mValue.Truncate();
+      txXPathNodeUtils::appendNodeValue(nodeSet->get(i), strResult->mValue);
+      if (compareResults(aContext, aLeft, strResult)) {
+        return true;
+      }
+    }
+
+    return false;
+  }
+
+  // Neither is a NodeSet
+  if (mOp == EQUAL || mOp == NOT_EQUAL) {
+    bool result;
+    const nsString *lString, *rString;
+
+    // If either is a bool, compare as bools.
+    if (ltype == txAExprResult::BOOLEAN || rtype == txAExprResult::BOOLEAN) {
+      result = aLeft->booleanValue() == aRight->booleanValue();
+    }
+
+    // If either is a number, compare as numbers.
+    else if (ltype == txAExprResult::NUMBER || rtype == txAExprResult::NUMBER) {
+      double lval = aLeft->numberValue();
+      double rval = aRight->numberValue();
+      result = (lval == rval);
+    }
+
+    // Otherwise compare as strings. Try to use the stringobject in
+    // StringResult if possible since that is a common case.
+    else if ((lString = aLeft->stringValuePointer())) {
+      if ((rString = aRight->stringValuePointer())) {
+        result = lString->Equals(*rString);
+      } else {
+        nsAutoString rStr;
+        aRight->stringValue(rStr);
+        result = lString->Equals(rStr);
+      }
+    } else if ((rString = aRight->stringValuePointer())) {
+      nsAutoString lStr;
+      aLeft->stringValue(lStr);
+      result = rString->Equals(lStr);
+    } else {
+      nsAutoString lStr, rStr;
+      aLeft->stringValue(lStr);
+      aRight->stringValue(rStr);
+      result = lStr.Equals(rStr);
+    }
+
+    return mOp == EQUAL ? result : !result;
+  }
+
+  double leftDbl = aLeft->numberValue();
+  double rightDbl = aRight->numberValue();
+  switch (mOp) {
+    case LESS_THAN: {
+      return (leftDbl < rightDbl);
+    }
+    case LESS_OR_EQUAL: {
+      return (leftDbl <= rightDbl);
+    }
+    case GREATER_THAN: {
+      return (leftDbl > rightDbl);
+    }
+    case GREATER_OR_EQUAL: {
+      return (leftDbl >= rightDbl);
+    }
+    default: {
+      MOZ_ASSERT_UNREACHABLE("We should have caught all cases");
+    }
+  }
+
+  return false;
+}
+
+nsresult RelationalExpr::evaluate(txIEvalContext* aContext,
+                                  txAExprResult** aResult) {
+  *aResult = nullptr;
+  RefPtr<txAExprResult> lResult;
+  nsresult rv = mLeftExpr->evaluate(aContext, getter_AddRefs(lResult));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  RefPtr<txAExprResult> rResult;
+  rv = mRightExpr->evaluate(aContext, getter_AddRefs(rResult));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  aContext->recycler()->getBoolResult(
+      compareResults(aContext, lResult, rResult), aResult);
+
+  return NS_OK;
+}
+
+TX_IMPL_EXPR_STUBS_2(RelationalExpr, BOOLEAN_RESULT, mLeftExpr, mRightExpr)
+
+bool RelationalExpr::isSensitiveTo(ContextSensitivity aContext) {
+  return mLeftExpr->isSensitiveTo(aContext) ||
+         mRightExpr->isSensitiveTo(aContext);
+}
+
+#ifdef TX_TO_STRING
+void RelationalExpr::toString(nsAString& str) {
+  mLeftExpr->toString(str);
+
+  switch (mOp) {
+    case NOT_EQUAL:
+      str.AppendLiteral("!=");
+      break;
+    case LESS_THAN:
+      str.Append(char16_t('<'));
+      break;
+    case LESS_OR_EQUAL:
+      str.AppendLiteral("<=");
+      break;
+    case GREATER_THAN:
+      str.Append(char16_t('>'));
+      break;
+    case GREATER_OR_EQUAL:
+      str.AppendLiteral(">=");
+      break;
+    default:
+      str.Append(char16_t('='));
+      break;
+  }
+
+  mRightExpr->toString(str);
+}
+#endif
diff --git a/dom/xslt/xpath/txResultRecycler.cpp b/dom/xslt/xpath/txResultRecycler.cpp
new file mode 100644
index 0000000000..b52f91838a
--- /dev/null
+++ b/dom/xslt/xpath/txResultRecycler.cpp
@@ -0,0 +1,171 @@
+/* -*- Mode: C++; tab-width: 4; 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/. */
+
+#include "txResultRecycler.h"
+#include "txExprResult.h"
+#include "txNodeSet.h"
+
+txResultRecycler::txResultRecycler()
+    : mEmptyStringResult(new StringResult(nullptr)),
+      mTrueResult(new BooleanResult(true)),
+      mFalseResult(new BooleanResult(false)) {}
+
+txResultRecycler::~txResultRecycler() {
+  txStackIterator stringIter(&mStringResults);
+  while (stringIter.hasNext()) {
+    delete static_cast<StringResult*>(stringIter.next());
+  }
+  txStackIterator nodesetIter(&mNodeSetResults);
+  while (nodesetIter.hasNext()) {
+    delete static_cast<txNodeSet*>(nodesetIter.next());
+  }
+  txStackIterator numberIter(&mNumberResults);
+  while (numberIter.hasNext()) {
+    delete static_cast<NumberResult*>(numberIter.next());
+  }
+}
+
+void txResultRecycler::recycle(txAExprResult* aResult) {
+  NS_ASSERTION(aResult->mRefCnt == 0, "In-use txAExprResult recycled");
+  RefPtr<txResultRecycler> kungFuDeathGrip;
+  aResult->mRecycler.swap(kungFuDeathGrip);
+
+  switch (aResult->getResultType()) {
+    case txAExprResult::STRING: {
+      mStringResults.push(static_cast<StringResult*>(aResult));
+      return;
+    }
+    case txAExprResult::NODESET: {
+      static_cast<txNodeSet*>(aResult)->clear();
+      mNodeSetResults.push(static_cast<txNodeSet*>(aResult));
+      return;
+    }
+    case txAExprResult::NUMBER: {
+      mNumberResults.push(static_cast<NumberResult*>(aResult));
+      return;
+    }
+    default: {
+      delete aResult;
+    }
+  }
+}
+
+nsresult txResultRecycler::getStringResult(StringResult** aResult) {
+  if (mStringResults.isEmpty()) {
+    *aResult = new StringResult(this);
+  } else {
+    *aResult = static_cast<StringResult*>(mStringResults.pop());
+    (*aResult)->mValue.Truncate();
+    (*aResult)->mRecycler = this;
+  }
+  NS_ADDREF(*aResult);
+
+  return NS_OK;
+}
+
+nsresult txResultRecycler::getStringResult(const nsAString& aValue,
+                                           txAExprResult** aResult) {
+  if (mStringResults.isEmpty()) {
+    *aResult = new StringResult(aValue, this);
+  } else {
+    StringResult* strRes = static_cast<StringResult*>(mStringResults.pop());
+    strRes->mValue = aValue;
+    strRes->mRecycler = this;
+    *aResult = strRes;
+  }
+  NS_ADDREF(*aResult);
+
+  return NS_OK;
+}
+
+void txResultRecycler::getEmptyStringResult(txAExprResult** aResult) {
+  *aResult = mEmptyStringResult;
+  NS_ADDREF(*aResult);
+}
+
+nsresult txResultRecycler::getNodeSet(txNodeSet** aResult) {
+  if (mNodeSetResults.isEmpty()) {
+    *aResult = new txNodeSet(this);
+  } else {
+    *aResult = static_cast<txNodeSet*>(mNodeSetResults.pop());
+    (*aResult)->mRecycler = this;
+  }
+  NS_ADDREF(*aResult);
+
+  return NS_OK;
+}
+
+nsresult txResultRecycler::getNodeSet(txNodeSet* aNodeSet,
+                                      txNodeSet** aResult) {
+  if (mNodeSetResults.isEmpty()) {
+    *aResult = new txNodeSet(*aNodeSet, this);
+  } else {
+    *aResult = static_cast<txNodeSet*>(mNodeSetResults.pop());
+    (*aResult)->append(*aNodeSet);
+    (*aResult)->mRecycler = this;
+  }
+  NS_ADDREF(*aResult);
+
+  return NS_OK;
+}
+
+nsresult txResultRecycler::getNodeSet(const txXPathNode& aNode,
+                                      txAExprResult** aResult) {
+  if (mNodeSetResults.isEmpty()) {
+    *aResult = new txNodeSet(aNode, this);
+  } else {
+    txNodeSet* nodes = static_cast<txNodeSet*>(mNodeSetResults.pop());
+    nodes->append(aNode);
+    nodes->mRecycler = this;
+    *aResult = nodes;
+  }
+  NS_ADDREF(*aResult);
+
+  return NS_OK;
+}
+
+nsresult txResultRecycler::getNumberResult(double aValue,
+                                           txAExprResult** aResult) {
+  if (mNumberResults.isEmpty()) {
+    *aResult = new NumberResult(aValue, this);
+  } else {
+    NumberResult* numRes = static_cast<NumberResult*>(mNumberResults.pop());
+    numRes->value = aValue;
+    numRes->mRecycler = this;
+    *aResult = numRes;
+  }
+  NS_ADDREF(*aResult);
+
+  return NS_OK;
+}
+
+void txResultRecycler::getBoolResult(bool aValue, txAExprResult** aResult) {
+  *aResult = aValue ? mTrueResult : mFalseResult;
+  NS_ADDREF(*aResult);
+}
+
+nsresult txResultRecycler::getNonSharedNodeSet(txNodeSet* aNodeSet,
+                                               txNodeSet** aResult) {
+  if (aNodeSet->mRefCnt > 1) {
+    return getNodeSet(aNodeSet, aResult);
+  }
+
+  *aResult = aNodeSet;
+  NS_ADDREF(*aResult);
+
+  return NS_OK;
+}
+
+void txAExprResult::Release() {
+  --mRefCnt;
+  NS_LOG_RELEASE(this, mRefCnt, "txAExprResult");
+  if (mRefCnt == 0) {
+    if (mRecycler) {
+      mRecycler->recycle(this);
+    } else {
+      delete this;
+    }
+  }
+}
diff --git a/dom/xslt/xpath/txResultRecycler.h b/dom/xslt/xpath/txResultRecycler.h
new file mode 100644
index 0000000000..f90687b70b
--- /dev/null
+++ b/dom/xslt/xpath/txResultRecycler.h
@@ -0,0 +1,76 @@
+/* -*- Mode: C++; tab-width: 4; 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 txResultRecycler_h__
+#define txResultRecycler_h__
+
+#include "nsCOMPtr.h"
+#include "txStack.h"
+
+class txAExprResult;
+class StringResult;
+class txNodeSet;
+class txXPathNode;
+class NumberResult;
+class BooleanResult;
+
+class txResultRecycler {
+ public:
+  txResultRecycler();
+  ~txResultRecycler();
+
+  void AddRef() {
+    ++mRefCnt;
+    NS_LOG_ADDREF(this, mRefCnt, "txResultRecycler", sizeof(*this));
+  }
+  void Release() {
+    --mRefCnt;
+    NS_LOG_RELEASE(this, mRefCnt, "txResultRecycler");
+    if (mRefCnt == 0) {
+      mRefCnt = 1;  // stabilize
+      delete this;
+    }
+  }
+
+  /**
+   * Returns an txAExprResult to this recycler for reuse.
+   * @param aResult  result to recycle
+   */
+  void recycle(txAExprResult* aResult);
+
+  /**
+   * Functions to return results that will be fully used by the caller.
+   * Returns nullptr on out-of-memory and an inited result otherwise.
+   */
+  nsresult getStringResult(StringResult** aResult);
+  nsresult getStringResult(const nsAString& aValue, txAExprResult** aResult);
+  nsresult getNodeSet(txNodeSet** aResult);
+  nsresult getNodeSet(txNodeSet* aNodeSet, txNodeSet** aResult);
+  nsresult getNodeSet(const txXPathNode& aNode, txAExprResult** aResult);
+  nsresult getNumberResult(double aValue, txAExprResult** aResult);
+
+  /**
+   * Functions to return a txAExprResult that is shared across several
+   * clients and must not be modified. Never returns nullptr.
+   */
+  void getEmptyStringResult(txAExprResult** aResult);
+  void getBoolResult(bool aValue, txAExprResult** aResult);
+
+  /**
+   * Functions that return non-shared resultsobjects
+   */
+  nsresult getNonSharedNodeSet(txNodeSet* aNodeSet, txNodeSet** aResult);
+
+ private:
+  nsAutoRefCnt mRefCnt;
+  txStack mStringResults;
+  txStack mNodeSetResults;
+  txStack mNumberResults;
+  RefPtr<StringResult> mEmptyStringResult;
+  RefPtr<BooleanResult> mTrueResult;
+  RefPtr<BooleanResult> mFalseResult;
+};
+
+#endif  // txResultRecycler_h__
diff --git a/dom/xslt/xpath/txRootExpr.cpp b/dom/xslt/xpath/txRootExpr.cpp
new file mode 100644
index 0000000000..cabc0e1c13
--- /dev/null
+++ b/dom/xslt/xpath/txRootExpr.cpp
@@ -0,0 +1,35 @@
+/* -*- Mode: C++; tab-width: 4; 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/. */
+
+#include "txExpr.h"
+#include "txNodeSet.h"
+#include "txIXPathContext.h"
+#include "txXPathTreeWalker.h"
+
+/**
+ * Evaluates this Expr based on the given context node and processor state
+ * @param context the context node for evaluation of this Expr
+ * @param ps the ContextState containing the stack information needed
+ * for evaluation
+ * @return the result of the evaluation
+ **/
+nsresult RootExpr::evaluate(txIEvalContext* aContext, txAExprResult** aResult) {
+  txXPathTreeWalker walker(aContext->getContextNode());
+  walker.moveToRoot();
+
+  return aContext->recycler()->getNodeSet(walker.getCurrentPosition(), aResult);
+}
+
+TX_IMPL_EXPR_STUBS_0(RootExpr, NODESET_RESULT)
+
+bool RootExpr::isSensitiveTo(ContextSensitivity aContext) {
+  return !!(aContext & NODE_CONTEXT);
+}
+
+#ifdef TX_TO_STRING
+void RootExpr::toString(nsAString& dest) {
+  if (mSerialize) dest.Append(char16_t('/'));
+}
+#endif
diff --git a/dom/xslt/xpath/txSingleNodeContext.h b/dom/xslt/xpath/txSingleNodeContext.h
new file mode 100644
index 0000000000..80b0680a2d
--- /dev/null
+++ b/dom/xslt/xpath/txSingleNodeContext.h
@@ -0,0 +1,64 @@
+/* -*- Mode: C++; tab-width: 4; 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 __TX_XPATH_SINGLENODE_CONTEXT
+#define __TX_XPATH_SINGLENODE_CONTEXT
+
+#include "mozilla/Attributes.h"
+#include "txIXPathContext.h"
+
+class txSingleNodeContext : public txIEvalContext {
+ public:
+  txSingleNodeContext(const txXPathNode& aContextNode,
+                      txIMatchContext* aContext)
+      : mNode(aContextNode), mInner(aContext) {
+    NS_ASSERTION(aContext, "txIMatchContext must be given");
+  }
+
+  nsresult getVariable(int32_t aNamespace, nsAtom* aLName,
+                       txAExprResult*& aResult) override {
+    NS_ASSERTION(mInner, "mInner is null!!!");
+    return mInner->getVariable(aNamespace, aLName, aResult);
+  }
+
+  nsresult isStripSpaceAllowed(const txXPathNode& aNode,
+                               bool& aAllowed) override {
+    NS_ASSERTION(mInner, "mInner is null!!!");
+    return mInner->isStripSpaceAllowed(aNode, aAllowed);
+  }
+
+  void* getPrivateContext() override {
+    NS_ASSERTION(mInner, "mInner is null!!!");
+    return mInner->getPrivateContext();
+  }
+
+  txResultRecycler* recycler() override {
+    NS_ASSERTION(mInner, "mInner is null!!!");
+    return mInner->recycler();
+  }
+
+  void receiveError(const nsAString& aMsg, nsresult aRes) override {
+    NS_ASSERTION(mInner, "mInner is null!!!");
+#ifdef DEBUG
+    nsAutoString error(u"forwarded error: "_ns);
+    error.Append(aMsg);
+    mInner->receiveError(error, aRes);
+#else
+    mInner->receiveError(aMsg, aRes);
+#endif
+  }
+
+  const txXPathNode& getContextNode() override { return mNode; }
+
+  uint32_t size() override { return 1; }
+
+  uint32_t position() override { return 1; }
+
+ private:
+  const txXPathNode& mNode;
+  txIMatchContext* mInner;
+};
+
+#endif  // __TX_XPATH_SINGLENODE_CONTEXT
diff --git a/dom/xslt/xpath/txStringResult.cpp b/dom/xslt/xpath/txStringResult.cpp
new file mode 100644
index 0000000000..740b6f1b34
--- /dev/null
+++ b/dom/xslt/xpath/txStringResult.cpp
@@ -0,0 +1,43 @@
+/* -*- Mode: C++; tab-width: 4; 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/. */
+
+/**
+ * StringResult
+ * Represents a String as a Result of evaluating an Expr
+ **/
+#include "txExprResult.h"
+
+/**
+ * Default Constructor
+ **/
+StringResult::StringResult(txResultRecycler* aRecycler)
+    : txAExprResult(aRecycler) {}
+
+/**
+ * Creates a new StringResult with the value of the given String parameter
+ * @param str the String to use for initialization of this StringResult's value
+ **/
+StringResult::StringResult(const nsAString& aValue, txResultRecycler* aRecycler)
+    : txAExprResult(aRecycler), mValue(aValue) {}
+
+/*
+ * Virtual Methods from ExprResult
+ */
+
+short StringResult::getResultType() {
+  return txAExprResult::STRING;
+}  //-- getResultType
+
+void StringResult::stringValue(nsString& aResult) { aResult.Append(mValue); }
+
+const nsString* StringResult::stringValuePointer() { return &mValue; }
+
+bool StringResult::booleanValue() {
+  return !mValue.IsEmpty();
+}  //-- booleanValue
+
+double StringResult::numberValue() {
+  return txDouble::toDouble(mValue);
+}  //-- numberValue
diff --git a/dom/xslt/xpath/txUnaryExpr.cpp b/dom/xslt/xpath/txUnaryExpr.cpp
new file mode 100644
index 0000000000..ec31a5fcb3
--- /dev/null
+++ b/dom/xslt/xpath/txUnaryExpr.cpp
@@ -0,0 +1,49 @@
+/* -*- Mode: C++; tab-width: 4; 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/. */
+
+#include "txExpr.h"
+#include "txIXPathContext.h"
+
+/*
+ * Evaluates this Expr based on the given context node and processor state
+ * @param context the context node for evaluation of this Expr
+ * @param ps the ContextState containing the stack information needed
+ * for evaluation.
+ * @return the result of the evaluation.
+ */
+nsresult UnaryExpr::evaluate(txIEvalContext* aContext,
+                             txAExprResult** aResult) {
+  *aResult = nullptr;
+
+  RefPtr<txAExprResult> exprRes;
+  nsresult rv = expr->evaluate(aContext, getter_AddRefs(exprRes));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  double value = exprRes->numberValue();
+#ifdef HPUX
+  /*
+   * Negation of a zero doesn't produce a negative
+   * zero on HPUX. Perform the operation by multiplying with
+   * -1.
+   */
+  return aContext->recycler()->getNumberResult(-1 * value, aResult);
+#else
+  return aContext->recycler()->getNumberResult(-value, aResult);
+#endif
+}
+
+TX_IMPL_EXPR_STUBS_1(UnaryExpr, NODESET_RESULT, expr)
+
+bool UnaryExpr::isSensitiveTo(ContextSensitivity aContext) {
+  return expr->isSensitiveTo(aContext);
+}
+
+#ifdef TX_TO_STRING
+void UnaryExpr::toString(nsAString& str) {
+  if (!expr) return;
+  str.Append(char16_t('-'));
+  expr->toString(str);
+}
+#endif
diff --git a/dom/xslt/xpath/txUnionExpr.cpp b/dom/xslt/xpath/txUnionExpr.cpp
new file mode 100644
index 0000000000..be8fa47781
--- /dev/null
+++ b/dom/xslt/xpath/txUnionExpr.cpp
@@ -0,0 +1,85 @@
+/* -*- Mode: C++; tab-width: 4; 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/. */
+
+#include "txExpr.h"
+#include "txIXPathContext.h"
+#include "txNodeSet.h"
+
+#ifdef TX_TO_STRING
+#  include "nsReadableUtils.h"
+#endif
+
+//-------------/
+//- UnionExpr -/
+//-------------/
+
+//-----------------------------/
+//- Virtual methods from Expr -/
+//-----------------------------/
+
+/**
+ * Evaluates this Expr based on the given context node and processor state
+ * @param context the context node for evaluation of this Expr
+ * @param ps the ContextState containing the stack information needed
+ * for evaluation
+ * @return the result of the evaluation
+ **/
+nsresult UnionExpr::evaluate(txIEvalContext* aContext,
+                             txAExprResult** aResult) {
+  *aResult = nullptr;
+  RefPtr<txNodeSet> nodes;
+  nsresult rv = aContext->recycler()->getNodeSet(getter_AddRefs(nodes));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  uint32_t i, len = mExpressions.Length();
+  for (i = 0; i < len; ++i) {
+    RefPtr<txAExprResult> exprResult;
+    rv = mExpressions[i]->evaluate(aContext, getter_AddRefs(exprResult));
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    if (exprResult->getResultType() != txAExprResult::NODESET) {
+      // XXX ErrorReport: report nonnodeset error
+      return NS_ERROR_XSLT_NODESET_EXPECTED;
+    }
+
+    RefPtr<txNodeSet> resultSet, ownedSet;
+    resultSet =
+        static_cast<txNodeSet*>(static_cast<txAExprResult*>(exprResult));
+    exprResult = nullptr;
+    rv = aContext->recycler()->getNonSharedNodeSet(resultSet,
+                                                   getter_AddRefs(ownedSet));
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    rv = nodes->addAndTransfer(ownedSet);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
+  *aResult = nodes;
+  NS_ADDREF(*aResult);
+
+  return NS_OK;
+}  //-- evaluate
+
+Expr::ExprType UnionExpr::getType() { return UNION_EXPR; }
+
+TX_IMPL_EXPR_STUBS_LIST(UnionExpr, NODESET_RESULT, mExpressions)
+
+bool UnionExpr::isSensitiveTo(ContextSensitivity aContext) {
+  uint32_t i, len = mExpressions.Length();
+  for (i = 0; i < len; ++i) {
+    if (mExpressions[i]->isSensitiveTo(aContext)) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+#ifdef TX_TO_STRING
+void UnionExpr::toString(nsAString& aDest) {
+  StringJoinAppend(aDest, u" | "_ns, mExpressions,
+                   [](nsAString& dest, Expr* expr) { expr->toString(dest); });
+}
+#endif
diff --git a/dom/xslt/xpath/txUnionNodeTest.cpp b/dom/xslt/xpath/txUnionNodeTest.cpp
new file mode 100644
index 0000000000..4461b537e4
--- /dev/null
+++ b/dom/xslt/xpath/txUnionNodeTest.cpp
@@ -0,0 +1,59 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* 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 "mozilla/FloatingPoint.h"
+
+#include "txExpr.h"
+#include "txExprResult.h"
+#include "txSingleNodeContext.h"
+
+#ifdef TX_TO_STRING
+#  include "nsReadableUtils.h"
+#endif
+
+nsresult txUnionNodeTest::matches(const txXPathNode& aNode,
+                                  txIMatchContext* aContext, bool& aMatched) {
+  uint32_t i, len = mNodeTests.Length();
+  for (i = 0; i < len; ++i) {
+    nsresult rv = mNodeTests[i]->matches(aNode, aContext, aMatched);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    if (aMatched) {
+      return NS_OK;
+    }
+  }
+
+  aMatched = false;
+  return NS_OK;
+}
+
+double txUnionNodeTest::getDefaultPriority() {
+  NS_ERROR("Don't call getDefaultPriority on txUnionPattern");
+  return mozilla::UnspecifiedNaN<double>();
+}
+
+bool txUnionNodeTest::isSensitiveTo(Expr::ContextSensitivity aContext) {
+  uint32_t i, len = mNodeTests.Length();
+  for (i = 0; i < len; ++i) {
+    if (mNodeTests[i]->isSensitiveTo(aContext)) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+#ifdef TX_TO_STRING
+void txUnionNodeTest::toString(nsAString& aDest) {
+  aDest.Append('(');
+
+  StringJoinAppend(
+      aDest, u" | "_ns, mNodeTests,
+      [](nsAString& dest, txNodeTest* nodeTest) { nodeTest->toString(dest); });
+
+  aDest.Append(')');
+}
+#endif
diff --git a/dom/xslt/xpath/txVariableRefExpr.cpp b/dom/xslt/xpath/txVariableRefExpr.cpp
new file mode 100644
index 0000000000..4836913135
--- /dev/null
+++ b/dom/xslt/xpath/txVariableRefExpr.cpp
@@ -0,0 +1,62 @@
+/* -*- Mode: C++; tab-width: 4; 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/. */
+
+#include "txExpr.h"
+#include "nsAtom.h"
+#include "txNodeSet.h"
+#include "nsGkAtoms.h"
+#include "txIXPathContext.h"
+
+//-------------------/
+//- VariableRefExpr -/
+//-------------------/
+
+/**
+ * Creates a VariableRefExpr with the given variable name
+ **/
+VariableRefExpr::VariableRefExpr(nsAtom* aPrefix, nsAtom* aLocalName,
+                                 int32_t aNSID)
+    : mPrefix(aPrefix), mLocalName(aLocalName), mNamespace(aNSID) {
+  NS_ASSERTION(mLocalName, "VariableRefExpr without local name?");
+  if (mPrefix == nsGkAtoms::_empty) mPrefix = nullptr;
+}
+
+/**
+ * Evaluates this Expr based on the given context node and processor state
+ * @param context the context node for evaluation of this Expr
+ * @param ps the ContextState containing the stack information needed
+ * for evaluation
+ * @return the result of the evaluation
+ **/
+nsresult VariableRefExpr::evaluate(txIEvalContext* aContext,
+                                   txAExprResult** aResult) {
+  nsresult rv = aContext->getVariable(mNamespace, mLocalName, *aResult);
+  if (NS_FAILED(rv)) {
+    // XXX report error, undefined variable
+    return rv;
+  }
+  return NS_OK;
+}
+
+TX_IMPL_EXPR_STUBS_0(VariableRefExpr, ANY_RESULT)
+
+bool VariableRefExpr::isSensitiveTo(ContextSensitivity aContext) {
+  return !!(aContext & VARIABLES_CONTEXT);
+}
+
+#ifdef TX_TO_STRING
+void VariableRefExpr::toString(nsAString& aDest) {
+  aDest.Append(char16_t('$'));
+  if (mPrefix) {
+    nsAutoString prefix;
+    mPrefix->ToString(prefix);
+    aDest.Append(prefix);
+    aDest.Append(char16_t(':'));
+  }
+  nsAutoString lname;
+  mLocalName->ToString(lname);
+  aDest.Append(lname);
+}
+#endif
diff --git a/dom/xslt/xpath/txXPathNode.h b/dom/xslt/xpath/txXPathNode.h
new file mode 100644
index 0000000000..8c5d6f5308
--- /dev/null
+++ b/dom/xslt/xpath/txXPathNode.h
@@ -0,0 +1,91 @@
+/* -*- Mode: C++; tab-width: 4; 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 txXPathNode_h__
+#define txXPathNode_h__
+
+#include "nsIContent.h"
+#include "mozilla/dom/Document.h"
+#include "nsINode.h"
+#include "nsNameSpaceManager.h"
+
+using txXPathNodeType = nsINode;
+
+class txXPathNode {
+ public:
+  bool operator==(const txXPathNode& aNode) const;
+  bool operator!=(const txXPathNode& aNode) const { return !(*this == aNode); }
+  ~txXPathNode();
+
+ private:
+  friend class txNodeSet;
+  friend class txXPathNativeNode;
+  friend class txXPathNodeUtils;
+  friend class txXPathTreeWalker;
+
+  txXPathNode(const txXPathNode& aNode);
+
+  explicit txXPathNode(mozilla::dom::Document* aDocument)
+      : mNode(aDocument), mRefCountRoot(0), mIndex(eDocument) {
+    MOZ_COUNT_CTOR(txXPathNode);
+  }
+  txXPathNode(nsINode* aNode, uint32_t aIndex, nsINode* aRoot)
+      : mNode(aNode), mRefCountRoot(aRoot ? 1 : 0), mIndex(aIndex) {
+    MOZ_COUNT_CTOR(txXPathNode);
+    if (aRoot) {
+      NS_ADDREF(aRoot);
+    }
+  }
+
+  static nsINode* RootOf(nsINode* aNode) { return aNode->SubtreeRoot(); }
+  nsINode* Root() const { return RootOf(mNode); }
+  nsINode* GetRootToAddRef() const { return mRefCountRoot ? Root() : nullptr; }
+
+  bool isDocument() const { return mIndex == eDocument; }
+  bool isContent() const { return mIndex == eContent; }
+  bool isAttribute() const { return mIndex != eDocument && mIndex != eContent; }
+
+  nsIContent* Content() const {
+    NS_ASSERTION(isContent() || isAttribute(), "wrong type");
+    return static_cast<nsIContent*>(mNode);
+  }
+  mozilla::dom::Document* Document() const {
+    NS_ASSERTION(isDocument(), "wrong type");
+    return static_cast<mozilla::dom::Document*>(mNode);
+  }
+
+  enum PositionType { eDocument = (1 << 30), eContent = eDocument - 1 };
+
+  nsINode* mNode;
+  uint32_t mRefCountRoot : 1;
+  uint32_t mIndex : 31;
+};
+
+class txNamespaceManager {
+ public:
+  static int32_t getNamespaceID(const nsAString& aNamespaceURI);
+  static nsresult getNamespaceURI(const int32_t aID, nsAString& aResult);
+};
+
+/* static */
+inline int32_t txNamespaceManager::getNamespaceID(
+    const nsAString& aNamespaceURI) {
+  int32_t namespaceID = kNameSpaceID_Unknown;
+  nsNameSpaceManager::GetInstance()->RegisterNameSpace(aNamespaceURI,
+                                                       namespaceID);
+  return namespaceID;
+}
+
+/* static */
+inline nsresult txNamespaceManager::getNamespaceURI(const int32_t aID,
+                                                    nsAString& aResult) {
+  return nsNameSpaceManager::GetInstance()->GetNameSpaceURI(aID, aResult);
+}
+
+inline bool txXPathNode::operator==(const txXPathNode& aNode) const {
+  return mIndex == aNode.mIndex && mNode == aNode.mNode;
+}
+
+#endif /* txXPathNode_h__ */
diff --git a/dom/xslt/xpath/txXPathOptimizer.cpp b/dom/xslt/xpath/txXPathOptimizer.cpp
new file mode 100644
index 0000000000..40a94f674c
--- /dev/null
+++ b/dom/xslt/xpath/txXPathOptimizer.cpp
@@ -0,0 +1,246 @@
+/* -*- Mode: C++; tab-width: 4; 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/. */
+
+#include "mozilla/Assertions.h"
+#include "txXPathOptimizer.h"
+#include "txExprResult.h"
+#include "nsAtom.h"
+#include "nsGkAtoms.h"
+#include "txXPathNode.h"
+#include "txExpr.h"
+#include "txIXPathContext.h"
+
+using mozilla::UniquePtr;
+using mozilla::Unused;
+
+class txEarlyEvalContext : public txIEvalContext {
+ public:
+  explicit txEarlyEvalContext(txResultRecycler* aRecycler)
+      : mRecycler(aRecycler) {}
+
+  // txIEvalContext
+  nsresult getVariable(int32_t aNamespace, nsAtom* aLName,
+                       txAExprResult*& aResult) override {
+    MOZ_CRASH("shouldn't depend on this context");
+  }
+  nsresult isStripSpaceAllowed(const txXPathNode& aNode,
+                               bool& aAllowed) override {
+    MOZ_CRASH("shouldn't depend on this context");
+  }
+  void* getPrivateContext() override {
+    MOZ_CRASH("shouldn't depend on this context");
+  }
+  txResultRecycler* recycler() override { return mRecycler; }
+  void receiveError(const nsAString& aMsg, nsresult aRes) override {}
+  const txXPathNode& getContextNode() override {
+    MOZ_CRASH("shouldn't depend on this context");
+  }
+  uint32_t size() override { MOZ_CRASH("shouldn't depend on this context"); }
+  uint32_t position() override {
+    MOZ_CRASH("shouldn't depend on this context");
+  }
+
+ private:
+  txResultRecycler* mRecycler;
+};
+
+void txXPathOptimizer::optimize(Expr* aInExpr, Expr** aOutExpr) {
+  *aOutExpr = nullptr;
+
+  // First check if the expression will produce the same result
+  // under any context.
+  Expr::ExprType exprType = aInExpr->getType();
+  if (exprType != Expr::LITERAL_EXPR &&
+      !aInExpr->isSensitiveTo(Expr::ANY_CONTEXT)) {
+    RefPtr<txResultRecycler> recycler = new txResultRecycler;
+    txEarlyEvalContext context(recycler);
+    RefPtr<txAExprResult> exprRes;
+
+    // Don't throw if this fails since it could be that the expression
+    // is or contains an error-expression.
+    nsresult rv = aInExpr->evaluate(&context, getter_AddRefs(exprRes));
+    if (NS_SUCCEEDED(rv)) {
+      *aOutExpr = new txLiteralExpr(exprRes);
+    }
+
+    return;
+  }
+
+  // Then optimize sub expressions
+  uint32_t i = 0;
+  Expr* subExpr;
+  while ((subExpr = aInExpr->getSubExprAt(i))) {
+    Expr* newExpr = nullptr;
+    optimize(subExpr, &newExpr);
+    if (newExpr) {
+      delete subExpr;
+      aInExpr->setSubExprAt(i, newExpr);
+    }
+
+    ++i;
+  }
+
+  // Finally see if current expression can be optimized
+  switch (exprType) {
+    case Expr::LOCATIONSTEP_EXPR:
+      optimizeStep(aInExpr, aOutExpr);
+      return;
+
+    case Expr::PATH_EXPR:
+      optimizePath(aInExpr, aOutExpr);
+      return;
+
+    case Expr::UNION_EXPR:
+      optimizeUnion(aInExpr, aOutExpr);
+      return;
+
+    default:
+      return;
+  }
+}
+
+void txXPathOptimizer::optimizeStep(Expr* aInExpr, Expr** aOutExpr) {
+  LocationStep* step = static_cast<LocationStep*>(aInExpr);
+
+  if (step->getAxisIdentifier() == LocationStep::ATTRIBUTE_AXIS) {
+    // Test for @foo type steps.
+    txNameTest* nameTest = nullptr;
+    if (!step->getSubExprAt(0) &&
+        step->getNodeTest()->getType() == txNameTest::NAME_TEST &&
+        (nameTest = static_cast<txNameTest*>(step->getNodeTest()))
+                ->mLocalName != nsGkAtoms::_asterisk) {
+      *aOutExpr = new txNamedAttributeStep(
+          nameTest->mNamespace, nameTest->mPrefix, nameTest->mLocalName);
+      return;  // return since we no longer have a step-object.
+    }
+  }
+
+  // Test for predicates that can be combined into the nodetest
+  Expr* pred;
+  while ((pred = step->getSubExprAt(0)) &&
+         !pred->canReturnType(Expr::NUMBER_RESULT) &&
+         !pred->isSensitiveTo(Expr::NODESET_CONTEXT)) {
+    txNodeTest* predTest = new txPredicatedNodeTest(step->getNodeTest(), pred);
+    step->dropFirst();
+    step->setNodeTest(predTest);
+  }
+}
+
+void txXPathOptimizer::optimizePath(Expr* aInExpr, Expr** aOutExpr) {
+  PathExpr* path = static_cast<PathExpr*>(aInExpr);
+
+  uint32_t i;
+  Expr* subExpr;
+  // look for steps like "//foo" that can be turned into "/descendant::foo"
+  // and "//." that can be turned into "/descendant-or-self::node()"
+  for (i = 0; (subExpr = path->getSubExprAt(i)); ++i) {
+    if (path->getPathOpAt(i) == PathExpr::DESCENDANT_OP &&
+        subExpr->getType() == Expr::LOCATIONSTEP_EXPR &&
+        !subExpr->getSubExprAt(0)) {
+      LocationStep* step = static_cast<LocationStep*>(subExpr);
+      if (step->getAxisIdentifier() == LocationStep::CHILD_AXIS) {
+        step->setAxisIdentifier(LocationStep::DESCENDANT_AXIS);
+        path->setPathOpAt(i, PathExpr::RELATIVE_OP);
+      } else if (step->getAxisIdentifier() == LocationStep::SELF_AXIS) {
+        step->setAxisIdentifier(LocationStep::DESCENDANT_OR_SELF_AXIS);
+        path->setPathOpAt(i, PathExpr::RELATIVE_OP);
+      }
+    }
+  }
+
+  // look for expressions that start with a "./"
+  subExpr = path->getSubExprAt(0);
+  LocationStep* step;
+  if (subExpr->getType() == Expr::LOCATIONSTEP_EXPR && path->getSubExprAt(1) &&
+      path->getPathOpAt(1) != PathExpr::DESCENDANT_OP) {
+    step = static_cast<LocationStep*>(subExpr);
+    if (step->getAxisIdentifier() == LocationStep::SELF_AXIS &&
+        !step->getSubExprAt(0)) {
+      txNodeTest* test = step->getNodeTest();
+      if (test->getType() == txNodeTest::NODETYPE_TEST &&
+          (static_cast<txNodeTypeTest*>(test))->getNodeTestType() ==
+              txNodeTypeTest::NODE_TYPE) {
+        // We have a '.' as first step followed by a single '/'.
+
+        // Check if there are only two steps. If so, return the second
+        // as resulting expression.
+        if (!path->getSubExprAt(2)) {
+          *aOutExpr = path->getSubExprAt(1);
+          path->setSubExprAt(1, nullptr);
+
+          return;
+        }
+
+        // Just delete the '.' step and leave the rest of the PathExpr
+        path->deleteExprAt(0);
+      }
+    }
+  }
+}
+
+void txXPathOptimizer::optimizeUnion(Expr* aInExpr, Expr** aOutExpr) {
+  UnionExpr* uni = static_cast<UnionExpr*>(aInExpr);
+
+  // Check for expressions like "foo | bar" and
+  // "descendant::foo | descendant::bar"
+
+  uint32_t current;
+  Expr* subExpr;
+  for (current = 0; (subExpr = uni->getSubExprAt(current)); ++current) {
+    if (subExpr->getType() != Expr::LOCATIONSTEP_EXPR ||
+        subExpr->getSubExprAt(0)) {
+      continue;
+    }
+
+    LocationStep* currentStep = static_cast<LocationStep*>(subExpr);
+    LocationStep::LocationStepType axis = currentStep->getAxisIdentifier();
+
+    txUnionNodeTest* unionTest = nullptr;
+
+    // Check if there are any other steps with the same axis and merge
+    // them with currentStep
+    uint32_t i;
+    for (i = current + 1; (subExpr = uni->getSubExprAt(i)); ++i) {
+      if (subExpr->getType() != Expr::LOCATIONSTEP_EXPR ||
+          subExpr->getSubExprAt(0)) {
+        continue;
+      }
+
+      LocationStep* step = static_cast<LocationStep*>(subExpr);
+      if (step->getAxisIdentifier() != axis) {
+        continue;
+      }
+
+      // Create a txUnionNodeTest if needed
+      if (!unionTest) {
+        UniquePtr<txNodeTest> owner(unionTest = new txUnionNodeTest);
+        unionTest->addNodeTest(currentStep->getNodeTest());
+
+        currentStep->setNodeTest(unionTest);
+        Unused << owner.release();
+      }
+
+      // Merge the nodetest into the union
+      unionTest->addNodeTest(step->getNodeTest());
+
+      step->setNodeTest(nullptr);
+
+      // Remove the step from the UnionExpr
+      uni->deleteExprAt(i);
+      --i;
+    }
+
+    // Check if all expressions were merged into a single step. If so,
+    // return the step as the new expression.
+    if (unionTest && current == 0 && !uni->getSubExprAt(1)) {
+      // Make sure the step doesn't get deleted when the UnionExpr is
+      uni->setSubExprAt(0, nullptr);
+      *aOutExpr = currentStep;
+
+      // Return right away since we no longer have a union
+      return;
+    }
+  }
+}
diff --git a/dom/xslt/xpath/txXPathOptimizer.h b/dom/xslt/xpath/txXPathOptimizer.h
new file mode 100644
index 0000000000..84f00191e7
--- /dev/null
+++ b/dom/xslt/xpath/txXPathOptimizer.h
@@ -0,0 +1,30 @@
+/* -*- Mode: C++; tab-width: 4; 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 txXPathOptimizer_h__
+#define txXPathOptimizer_h__
+
+#include "txCore.h"
+
+class Expr;
+
+class txXPathOptimizer {
+ public:
+  /**
+   * Optimize the given expression.
+   * @param aInExpr       Expression to optimize.
+   * @param aOutExpr      Resulting expression, null if optimization didn't
+   *                      result in a new expression.
+   */
+  void optimize(Expr* aInExpr, Expr** aOutExpr);
+
+ private:
+  // Helper methods for optimizing specific classes
+  void optimizeStep(Expr* aInExpr, Expr** aOutExpr);
+  void optimizePath(Expr* aInExpr, Expr** aOutExpr);
+  void optimizeUnion(Expr* aInExpr, Expr** aOutExpr);
+};
+
+#endif
diff --git a/dom/xslt/xpath/txXPathTreeWalker.h b/dom/xslt/xpath/txXPathTreeWalker.h
new file mode 100644
index 0000000000..6b74b1e18d
--- /dev/null
+++ b/dom/xslt/xpath/txXPathTreeWalker.h
@@ -0,0 +1,201 @@
+/* -*- Mode: C++; tab-width: 4; 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 txXPathTreeWalker_h__
+#define txXPathTreeWalker_h__
+
+#include "txCore.h"
+#include "txXPathNode.h"
+#include "nsIContentInlines.h"
+#include "nsTArray.h"
+
+class nsAtom;
+
+class txXPathTreeWalker {
+ public:
+  txXPathTreeWalker(const txXPathTreeWalker& aOther);
+  explicit txXPathTreeWalker(const txXPathNode& aNode);
+
+  bool getAttr(nsAtom* aLocalName, int32_t aNSID, nsAString& aValue) const;
+  int32_t getNamespaceID() const;
+  uint16_t getNodeType() const;
+  void appendNodeValue(nsAString& aResult) const;
+  void getNodeName(nsAString& aName) const;
+
+  void moveTo(const txXPathTreeWalker& aWalker);
+
+  void moveToRoot();
+  bool moveToParent();
+  bool moveToElementById(const nsAString& aID);
+  bool moveToFirstAttribute();
+  bool moveToNextAttribute();
+  bool moveToNamedAttribute(nsAtom* aLocalName, int32_t aNSID);
+  bool moveToFirstChild();
+  bool moveToLastChild();
+  bool moveToNextSibling();
+  bool moveToPreviousSibling();
+
+  bool isOnNode(const txXPathNode& aNode) const;
+
+  const txXPathNode& getCurrentPosition() const;
+
+ private:
+  txXPathNode mPosition;
+
+  bool moveToValidAttribute(uint32_t aStartIndex);
+};
+
+class txXPathNodeUtils {
+ public:
+  static bool getAttr(const txXPathNode& aNode, nsAtom* aLocalName,
+                      int32_t aNSID, nsAString& aValue);
+  static already_AddRefed<nsAtom> getLocalName(const txXPathNode& aNode);
+  static nsAtom* getPrefix(const txXPathNode& aNode);
+  static void getLocalName(const txXPathNode& aNode, nsAString& aLocalName);
+  static void getNodeName(const txXPathNode& aNode, nsAString& aName);
+  static int32_t getNamespaceID(const txXPathNode& aNode);
+  static void getNamespaceURI(const txXPathNode& aNode, nsAString& aURI);
+  static uint16_t getNodeType(const txXPathNode& aNode);
+  static void appendNodeValue(const txXPathNode& aNode, nsAString& aResult);
+  static bool isWhitespace(const txXPathNode& aNode);
+  static txXPathNode* getOwnerDocument(const txXPathNode& aNode);
+  static int32_t getUniqueIdentifier(const txXPathNode& aNode);
+  static nsresult getXSLTId(const txXPathNode& aNode, const txXPathNode& aBase,
+                            nsAString& aResult);
+  static void release(txXPathNode* aNode);
+  static nsresult getBaseURI(const txXPathNode& aNode, nsAString& aURI);
+  static int comparePosition(const txXPathNode& aNode,
+                             const txXPathNode& aOtherNode);
+  static bool localNameEquals(const txXPathNode& aNode, nsAtom* aLocalName);
+  static bool isRoot(const txXPathNode& aNode);
+  static bool isElement(const txXPathNode& aNode);
+  static bool isAttribute(const txXPathNode& aNode);
+  static bool isProcessingInstruction(const txXPathNode& aNode);
+  static bool isComment(const txXPathNode& aNode);
+  static bool isText(const txXPathNode& aNode);
+  static inline bool isHTMLElementInHTMLDocument(const txXPathNode& aNode) {
+    if (!aNode.isContent()) {
+      return false;
+    }
+    nsIContent* content = aNode.Content();
+    return content->IsHTMLElement() && content->IsInHTMLDocument();
+  }
+};
+
+class txXPathNativeNode {
+ public:
+  static txXPathNode* createXPathNode(nsINode* aNode,
+                                      bool aKeepRootAlive = false);
+  static txXPathNode* createXPathNode(nsIContent* aContent,
+                                      bool aKeepRootAlive = false);
+  static txXPathNode* createXPathNode(mozilla::dom::Document* aDocument);
+  static nsINode* getNode(const txXPathNode& aNode);
+  static nsIContent* getContent(const txXPathNode& aNode);
+  static mozilla::dom::Document* getDocument(const txXPathNode& aNode);
+  static void addRef(const txXPathNode& aNode) { NS_ADDREF(aNode.mNode); }
+  static void release(const txXPathNode& aNode) {
+    nsINode* node = aNode.mNode;
+    NS_RELEASE(node);
+  }
+};
+
+inline const txXPathNode& txXPathTreeWalker::getCurrentPosition() const {
+  return mPosition;
+}
+
+inline bool txXPathTreeWalker::getAttr(nsAtom* aLocalName, int32_t aNSID,
+                                       nsAString& aValue) const {
+  return txXPathNodeUtils::getAttr(mPosition, aLocalName, aNSID, aValue);
+}
+
+inline int32_t txXPathTreeWalker::getNamespaceID() const {
+  return txXPathNodeUtils::getNamespaceID(mPosition);
+}
+
+inline void txXPathTreeWalker::appendNodeValue(nsAString& aResult) const {
+  txXPathNodeUtils::appendNodeValue(mPosition, aResult);
+}
+
+inline void txXPathTreeWalker::getNodeName(nsAString& aName) const {
+  txXPathNodeUtils::getNodeName(mPosition, aName);
+}
+
+inline void txXPathTreeWalker::moveTo(const txXPathTreeWalker& aWalker) {
+  nsINode* root = nullptr;
+  if (mPosition.mRefCountRoot) {
+    root = mPosition.Root();
+  }
+  mPosition.mIndex = aWalker.mPosition.mIndex;
+  mPosition.mRefCountRoot = aWalker.mPosition.mRefCountRoot;
+  mPosition.mNode = aWalker.mPosition.mNode;
+  nsINode* newRoot = nullptr;
+  if (mPosition.mRefCountRoot) {
+    newRoot = mPosition.Root();
+  }
+  if (root != newRoot) {
+    NS_IF_ADDREF(newRoot);
+    NS_IF_RELEASE(root);
+  }
+}
+
+inline bool txXPathTreeWalker::isOnNode(const txXPathNode& aNode) const {
+  return (mPosition == aNode);
+}
+
+/* static */
+inline int32_t txXPathNodeUtils::getUniqueIdentifier(const txXPathNode& aNode) {
+  MOZ_ASSERT(!aNode.isAttribute(), "Not implemented for attributes.");
+  return NS_PTR_TO_INT32(aNode.mNode);
+}
+
+/* static */
+inline void txXPathNodeUtils::release(txXPathNode* aNode) {
+  NS_RELEASE(aNode->mNode);
+}
+
+/* static */
+inline bool txXPathNodeUtils::localNameEquals(const txXPathNode& aNode,
+                                              nsAtom* aLocalName) {
+  if (aNode.isContent() && aNode.Content()->IsElement()) {
+    return aNode.Content()->NodeInfo()->Equals(aLocalName);
+  }
+
+  RefPtr<nsAtom> localName = txXPathNodeUtils::getLocalName(aNode);
+
+  return localName == aLocalName;
+}
+
+/* static */
+inline bool txXPathNodeUtils::isRoot(const txXPathNode& aNode) {
+  return !aNode.isAttribute() && !aNode.mNode->GetParentNode();
+}
+
+/* static */
+inline bool txXPathNodeUtils::isElement(const txXPathNode& aNode) {
+  return aNode.isContent() && aNode.Content()->IsElement();
+}
+
+/* static */
+inline bool txXPathNodeUtils::isAttribute(const txXPathNode& aNode) {
+  return aNode.isAttribute();
+}
+
+/* static */
+inline bool txXPathNodeUtils::isProcessingInstruction(
+    const txXPathNode& aNode) {
+  return aNode.isContent() && aNode.Content()->IsProcessingInstruction();
+}
+
+/* static */
+inline bool txXPathNodeUtils::isComment(const txXPathNode& aNode) {
+  return aNode.isContent() && aNode.Content()->IsComment();
+}
+
+/* static */
+inline bool txXPathNodeUtils::isText(const txXPathNode& aNode) {
+  return aNode.isContent() && aNode.Content()->IsText();
+}
+
+#endif /* txXPathTreeWalker_h__ */