Stop running pub get at gclient sync time and fix build bugs

mojo/public/dart/third_party/analyzer/lib/src/generated/html.dart

Index: mojo/public/dart/third_party/analyzer/lib/src/generated/html.dart
diff --git a/mojo/public/dart/third_party/analyzer/lib/src/generated/html.dart b/mojo/public/dart/third_party/analyzer/lib/src/generated/html.dart
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+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+library engine.html;
+
+import 'dart:collection';
+
+import 'ast.dart';
+import 'element.dart';
+import 'engine.dart' show AnalysisOptions, AnalysisEngine;
+import 'error.dart' show AnalysisErrorListener;
+import 'java_core.dart';
+import 'java_engine.dart';
+import 'parser.dart' show Parser;
+import 'scanner.dart' as sc show Scanner, SubSequenceReader, Token;
+import 'source.dart';
+
+/**
+ * The abstract class `AbstractScanner` implements a scanner for HTML code. Subclasses are
+ * required to implement the interface used to access the characters being scanned.
+ */
+abstract class AbstractScanner {
+  static List<String> _NO_PASS_THROUGH_ELEMENTS = <String>[];
+
+  /**
+   * The source being scanned.
+   */
+  final Source source;
+
+  /**
+   * The token pointing to the head of the linked list of tokens.
+   */
+  Token _tokens;
+
+  /**
+   * The last token that was scanned.
+   */
+  Token _tail;
+
+  /**
+   * A list containing the offsets of the first character of each line in the source code.
+   */
+  List<int> _lineStarts = new List<int>();
+
+  /**
+   * An array of element tags for which the content between tags should be consider a single token.
+   */
+  List<String> _passThroughElements = _NO_PASS_THROUGH_ELEMENTS;
+
+  /**
+   * Initialize a newly created scanner.
+   *
+   * @param source the source being scanned
+   */
+  AbstractScanner(this.source) {
+    _tokens = new Token.con1(TokenType.EOF, -1);
+    _tokens.setNext(_tokens);
+    _tail = _tokens;
+    recordStartOfLine();
+  }
+
+  /**
+   * Return an array containing the offsets of the first character of each line in the source code.
+   *
+   * @return an array containing the offsets of the first character of each line in the source code
+   */
+  List<int> get lineStarts => _lineStarts;
+
+  /**
+   * Return the current offset relative to the beginning of the file. Return the initial offset if
+   * the scanner has not yet scanned the source code, and one (1) past the end of the source code if
+   * the source code has been scanned.
+   *
+   * @return the current offset of the scanner in the source
+   */
+  int get offset;
+
+  /**
+   * Set array of element tags for which the content between tags should be consider a single token.
+   */
+  void set passThroughElements(List<String> passThroughElements) {
+    this._passThroughElements = passThroughElements != null
+        ? passThroughElements
+        : _NO_PASS_THROUGH_ELEMENTS;
+  }
+
+  /**
+   * Advance the current position and return the character at the new current position.
+   *
+   * @return the character at the new current position
+   */
+  int advance();
+
+  /**
+   * Return the substring of the source code between the start offset and the modified current
+   * position. The current position is modified by adding the end delta.
+   *
+   * @param start the offset to the beginning of the string, relative to the start of the file
+   * @param endDelta the number of character after the current location to be included in the
+   *          string, or the number of characters before the current location to be excluded if the
+   *          offset is negative
+   * @return the specified substring of the source code
+   */
+  String getString(int start, int endDelta);
+
+  /**
+   * Return the character at the current position without changing the current position.
+   *
+   * @return the character at the current position
+   */
+  int peek();
+
+  /**
+   * Record the fact that we are at the beginning of a new line in the source.
+   */
+  void recordStartOfLine() {
+    _lineStarts.add(offset);
+  }
+
+  /**
+   * Scan the source code to produce a list of tokens representing the source.
+   *
+   * @return the first token in the list of tokens that were produced
+   */
+  Token tokenize() {
+    _scan();
+    _appendEofToken();
+    return _firstToken();
+  }
+
+  void _appendEofToken() {
+    Token eofToken = new Token.con1(TokenType.EOF, offset);
+    // The EOF token points to itself so that there is always infinite
+    // look-ahead.
+    eofToken.setNext(eofToken);
+    _tail = _tail.setNext(eofToken);
+  }
+
+  Token _emit(Token token) {
+    _tail.setNext(token);
+    _tail = token;
+    return token;
+  }
+
+  Token _emitWithOffset(TokenType type, int start) =>
+      _emit(new Token.con1(type, start));
+
+  Token _emitWithOffsetAndLength(TokenType type, int start, int count) =>
+      _emit(new Token.con2(type, start, getString(start, count)));
+
+  Token _firstToken() => _tokens.next;
+
+  int _recordStartOfLineAndAdvance(int c) {
+    if (c == 0xD) {
+      c = advance();
+      if (c == 0xA) {
+        c = advance();
+      }
+      recordStartOfLine();
+    } else if (c == 0xA) {
+      c = advance();
+      recordStartOfLine();
+    } else {
+      c = advance();
+    }
+    return c;
+  }
+
+  void _scan() {
+    bool inBrackets = false;
+    String endPassThrough = null;
+    int c = advance();
+    while (c >= 0) {
+      int start = offset;
+      if (c == 0x3C) {
+        c = advance();
+        if (c == 0x21) {
+          c = advance();
+          if (c == 0x2D && peek() == 0x2D) {
+            // handle a comment
+            c = advance();
+            int dashCount = 1;
+            while (c >= 0) {
+              if (c == 0x2D) {
+                dashCount++;
+              } else if (c == 0x3E && dashCount >= 2) {
+                c = advance();
+                break;
+              } else {
+                dashCount = 0;
+              }
+              c = _recordStartOfLineAndAdvance(c);
+            }
+            _emitWithOffsetAndLength(TokenType.COMMENT, start, -1);
+            // Capture <!--> and <!---> as tokens but report an error
+            if (_tail.length < 7) {
+              // TODO (danrubel): Report invalid HTML comment
+            }
+          } else {
+            // handle a declaration
+            while (c >= 0) {
+              if (c == 0x3E) {
+                c = advance();
+                break;
+              }
+              c = _recordStartOfLineAndAdvance(c);
+            }
+            _emitWithOffsetAndLength(TokenType.DECLARATION, start, -1);
+            if (!StringUtilities.endsWithChar(_tail.lexeme, 0x3E)) {
+              // TODO (danrubel): Report missing '>' in directive
+            }
+          }
+        } else if (c == 0x3F) {
+          // handle a directive
+          while (c >= 0) {
+            if (c == 0x3F) {
+              c = advance();
+              if (c == 0x3E) {
+                c = advance();
+                break;
+              }
+            } else {
+              c = _recordStartOfLineAndAdvance(c);
+            }
+          }
+          _emitWithOffsetAndLength(TokenType.DIRECTIVE, start, -1);
+          if (_tail.length < 4) {
+            // TODO (danrubel): Report invalid directive
+          }
+        } else if (c == 0x2F) {
+          _emitWithOffset(TokenType.LT_SLASH, start);
+          inBrackets = true;
+          c = advance();
+        } else {
+          inBrackets = true;
+          _emitWithOffset(TokenType.LT, start);
+          // ignore whitespace in braces
+          while (Character.isWhitespace(c)) {
+            c = _recordStartOfLineAndAdvance(c);
+          }
+          // get tag
+          if (Character.isLetterOrDigit(c)) {
+            int tagStart = offset;
+            c = advance();
+            while (Character.isLetterOrDigit(c) || c == 0x2D || c == 0x5F) {
+              c = advance();
+            }
+            _emitWithOffsetAndLength(TokenType.TAG, tagStart, -1);
+            // check tag against passThrough elements
+            String tag = _tail.lexeme;
+            for (String str in _passThroughElements) {
+              if (str == tag) {
+                endPassThrough = "</$str>";
+                break;
+              }
+            }
+          }
+        }
+      } else if (c == 0x3E) {
+        _emitWithOffset(TokenType.GT, start);
+        inBrackets = false;
+        c = advance();
+        // if passThrough != null, read until we match it
+        if (endPassThrough != null) {
+          bool endFound = false;
+          int len = endPassThrough.length;
+          int firstC = endPassThrough.codeUnitAt(0);
+          int index = 0;
+          int nextC = firstC;
+          while (c >= 0) {
+            if (c == nextC) {
+              index++;
+              if (index == len) {
+                endFound = true;
+                break;
+              }
+              nextC = endPassThrough.codeUnitAt(index);
+            } else if (c == firstC) {
+              index = 1;
+              nextC = endPassThrough.codeUnitAt(1);
+            } else {
+              index = 0;
+              nextC = firstC;
+            }
+            c = _recordStartOfLineAndAdvance(c);
+          }
+          if (start + 1 < offset) {
+            if (endFound) {
+              _emitWithOffsetAndLength(TokenType.TEXT, start + 1, -len);
+              _emitWithOffset(TokenType.LT_SLASH, offset - len + 1);
+              _emitWithOffsetAndLength(TokenType.TAG, offset - len + 3, -1);
+            } else {
+              _emitWithOffsetAndLength(TokenType.TEXT, start + 1, -1);
+            }
+          }
+          endPassThrough = null;
+        }
+      } else if (c == 0x2F && peek() == 0x3E) {
+        advance();
+        _emitWithOffset(TokenType.SLASH_GT, start);
+        inBrackets = false;
+        c = advance();
+      } else if (!inBrackets) {
+        c = _recordStartOfLineAndAdvance(c);
+        while (c != 0x3C && c >= 0) {
+          c = _recordStartOfLineAndAdvance(c);
+        }
+        _emitWithOffsetAndLength(TokenType.TEXT, start, -1);
+      } else if (c == 0x22 || c == 0x27) {
+        // read a string
+        int endQuote = c;
+        c = advance();
+        while (c >= 0) {
+          if (c == endQuote) {
+            c = advance();
+            break;
+          }
+          c = _recordStartOfLineAndAdvance(c);
+        }
+        _emitWithOffsetAndLength(TokenType.STRING, start, -1);
+      } else if (c == 0x3D) {
+        // a non-char token
+        _emitWithOffset(TokenType.EQ, start);
+        c = advance();
+      } else if (Character.isWhitespace(c)) {
+        // ignore whitespace in braces
+        do {
+          c = _recordStartOfLineAndAdvance(c);
+        } while (Character.isWhitespace(c));
+      } else if (Character.isLetterOrDigit(c)) {
+        c = advance();
+        while (Character.isLetterOrDigit(c) || c == 0x2D || c == 0x5F) {
+          c = advance();
+        }
+        _emitWithOffsetAndLength(TokenType.TAG, start, -1);
+      } else {
+        // a non-char token
+        _emitWithOffsetAndLength(TokenType.TEXT, start, 0);
+        c = advance();
+      }
+    }
+  }
+}
+
+/**
+ * Instances of the class `HtmlParser` are used to parse tokens into a AST structure comprised
+ * of [XmlNode]s.
+ */
+class HtmlParser extends XmlParser {
+  static String _APPLICATION_DART_IN_DOUBLE_QUOTES = "\"application/dart\"";
+
+  static String _APPLICATION_DART_IN_SINGLE_QUOTES = "'application/dart'";
+
+  static String _SCRIPT = "script";
+
+  static String _TYPE = "type";
+
+  /**
+   * A set containing the names of tags that do not have a closing tag.
+   */
+  static Set<String> SELF_CLOSING = new HashSet<String>.from(<String>[
+    "area",
+    "base",
+    "basefont",
+    "br",
+    "col",
+    "frame",
+    "hr",
+    "img",
+    "input",
+    "link",
+    "meta",
+    "param",
+    "!"
+  ]);
+
+  /**
+   * The line information associated with the source being parsed.
+   */
+  LineInfo _lineInfo;
+
+  /**
+   * The error listener to which errors will be reported.
+   */
+  final AnalysisErrorListener _errorListener;
+
+  final AnalysisOptions _options;
+
+  /**
+   * Construct a parser for the specified source.
+   *
+   * [source] is the source being parsed.  [_errorListener] is the error
+   * listener to which errors will be reported.  [_options] is the analysis
+   * options which should be used for parsing.
+   */
+  HtmlParser(Source source, this._errorListener, this._options) : super(source);
+
+  @override
+  XmlAttributeNode createAttributeNode(Token name, Token equals, Token value) =>
+      new XmlAttributeNode(name, equals, value);
+
+  @override
+  XmlTagNode createTagNode(Token nodeStart, Token tag,
+      List<XmlAttributeNode> attributes, Token attributeEnd,
+      List<XmlTagNode> tagNodes, Token contentEnd, Token closingTag,
+      Token nodeEnd) {
+    if (_isScriptNode(tag, attributes, tagNodes)) {
+      HtmlScriptTagNode tagNode = new HtmlScriptTagNode(nodeStart, tag,
+          attributes, attributeEnd, tagNodes, contentEnd, closingTag, nodeEnd);
+      String contents = tagNode.content;
+      int contentOffset = attributeEnd.end;
+      LineInfo_Location location = _lineInfo.getLocation(contentOffset);
+      sc.Scanner scanner = new sc.Scanner(source,
+          new sc.SubSequenceReader(contents, contentOffset), _errorListener);
+      scanner.setSourceStart(location.lineNumber, location.columnNumber);
+      sc.Token firstToken = scanner.tokenize();
+      Parser parser = new Parser(source, _errorListener);
+      CompilationUnit unit = parser.parseCompilationUnit(firstToken);
+      unit.lineInfo = _lineInfo;
+      tagNode.script = unit;
+      return tagNode;
+    }
+    return new XmlTagNode(nodeStart, tag, attributes, attributeEnd, tagNodes,
+        contentEnd, closingTag, nodeEnd);
+  }
+
+  @override
+  bool isSelfClosing(Token tag) => SELF_CLOSING.contains(tag.lexeme);
+
+  /**
+   * Parse the given tokens.
+   *
+   * @param token the first token in the stream of tokens to be parsed
+   * @param lineInfo the line information created by the scanner
+   * @return the parse result (not `null`)
+   */
+  HtmlUnit parse(Token token, LineInfo lineInfo) {
+    this._lineInfo = lineInfo;
+    List<XmlTagNode> tagNodes = parseTopTagNodes(token);
+    return new HtmlUnit(token, tagNodes, currentToken);
+  }
+
+  /**
+   * Determine if the specified node is a Dart script.
+   *
+   * @param node the node to be tested (not `null`)
+   * @return `true` if the node is a Dart script
+   */
+  bool _isScriptNode(
+      Token tag, List<XmlAttributeNode> attributes, List<XmlTagNode> tagNodes) {
+    if (tagNodes.length != 0 || tag.lexeme != _SCRIPT) {
+      return false;
+    }
+    for (XmlAttributeNode attribute in attributes) {
+      if (attribute.name == _TYPE) {
+        Token valueToken = attribute.valueToken;
+        if (valueToken != null) {
+          String value = valueToken.lexeme;
+          if (value == _APPLICATION_DART_IN_DOUBLE_QUOTES ||
+              value == _APPLICATION_DART_IN_SINGLE_QUOTES) {
+            return true;
+          }
+        }
+      }
+    }
+    return false;
+  }
+
+  /**
+   * Given the contents of an embedded expression that occurs at the given offset, parse it as a
+   * Dart expression. The contents should not include the expression's delimiters.
+   *
+   * @param source the source that contains that given token
+   * @param token the token to start parsing from
+   * @return the Dart expression that was parsed
+   */
+  static Expression parseEmbeddedExpression(
+      Source source, sc.Token token, AnalysisErrorListener errorListener) {
+    Parser parser = new Parser(source, errorListener);
+    return parser.parseExpression(token);
+  }
+
+  /**
+   * Given the contents of an embedded expression that occurs at the given offset, scans it as a
+   * Dart code.
+   *
+   * @param source the source of that contains the given contents
+   * @param contents the contents to scan
+   * @param contentOffset the offset of the contents in the larger file
+   * @return the first Dart token
+   */
+  static sc.Token scanDartSource(Source source, LineInfo lineInfo,
+      String contents, int contentOffset, AnalysisErrorListener errorListener) {
+    LineInfo_Location location = lineInfo.getLocation(contentOffset);
+    sc.Scanner scanner = new sc.Scanner(source,
+        new sc.SubSequenceReader(contents, contentOffset), errorListener);
+    scanner.setSourceStart(location.lineNumber, location.columnNumber);
+    return scanner.tokenize();
+  }
+}
+
+/**
+ * Instances of the class `HtmlScriptTagNode` represent a script tag within an HTML file that
+ * references a Dart script.
+ */
+@deprecated
+class HtmlScriptTagNode extends XmlTagNode {
+  /**
+   * The AST structure representing the Dart code within this tag.
+   */
+  CompilationUnit _script;
+
+  /**
+   * The element representing this script.
+   */
+  HtmlScriptElement scriptElement;
+
+  /**
+   * Initialize a newly created node to represent a script tag within an HTML file that references a
+   * Dart script.
+   *
+   * @param nodeStart the token marking the beginning of the tag
+   * @param tag the name of the tag
+   * @param attributes the attributes in the tag
+   * @param attributeEnd the token terminating the region where attributes can be
+   * @param tagNodes the children of the tag
+   * @param contentEnd the token that starts the closing tag
+   * @param closingTag the name of the tag that occurs in the closing tag
+   * @param nodeEnd the last token in the tag
+   */
+  HtmlScriptTagNode(Token nodeStart, Token tag,
+      List<XmlAttributeNode> attributes, Token attributeEnd,
+      List<XmlTagNode> tagNodes, Token contentEnd, Token closingTag,
+      Token nodeEnd)
+      : super(nodeStart, tag, attributes, attributeEnd, tagNodes, contentEnd,
+          closingTag, nodeEnd);
+
+  /**
+   * Return the AST structure representing the Dart code within this tag, or `null` if this
+   * tag references an external script.
+   *
+   * @return the AST structure representing the Dart code within this tag
+   */
+  CompilationUnit get script => _script;
+
+  /**
+   * Set the AST structure representing the Dart code within this tag to the given compilation unit.
+   *
+   * @param unit the AST structure representing the Dart code within this tag
+   */
+  void set script(CompilationUnit unit) {
+    _script = unit;
+  }
+
+  @override
+  accept(XmlVisitor visitor) => visitor.visitHtmlScriptTagNode(this);
+}
+
+/**
+ * Instances of the class `HtmlUnit` represent the contents of an HTML file.
+ */
+@deprecated
+class HtmlUnit extends XmlNode {
+  /**
+   * The first token in the token stream that was parsed to form this HTML unit.
+   */
+  final Token beginToken;
+
+  /**
+   * The last token in the token stream that was parsed to form this compilation unit. This token
+   * should always have a type of [TokenType.EOF].
+   */
+  final Token endToken;
+
+  /**
+   * The tag nodes contained in the receiver (not `null`, contains no `null`s).
+   */
+  List<XmlTagNode> _tagNodes;
+
+  /**
+   * Construct a new instance representing the content of an HTML file.
+   *
+   * @param beginToken the first token in the file (not `null`)
+   * @param tagNodes child tag nodes of the receiver (not `null`, contains no `null`s)
+   * @param endToken the last token in the token stream which should be of type
+   *          [TokenType.EOF]
+   */
+  HtmlUnit(this.beginToken, List<XmlTagNode> tagNodes, this.endToken) {
+    this._tagNodes = becomeParentOfAll(tagNodes);
+  }
+
+  /**
+   * Return the element associated with this HTML unit.
+   *
+   * @return the element or `null` if the receiver is not resolved
+   */
+  @override
+  HtmlElement get element => super.element as HtmlElement;
+
+  @override
+  void set element(Element element) {
+    if (element != null && element is! HtmlElement) {
+      throw new IllegalArgumentException(
+          "HtmlElement expected, but ${element.runtimeType} given");
+    }
+    super.element = element;
+  }
+
+  /**
+   * Answer the tag nodes contained in the receiver. Callers should not manipulate the returned list
+   * to edit the AST structure.
+   *
+   * @return the children (not `null`, contains no `null`s)
+   */
+  List<XmlTagNode> get tagNodes => _tagNodes;
+
+  @override
+  accept(XmlVisitor visitor) => visitor.visitHtmlUnit(this);
+
+  @override
+  void visitChildren(XmlVisitor visitor) {
+    for (XmlTagNode node in _tagNodes) {
+      node.accept(visitor);
+    }
+  }
+}
+
+/**
+ * Instances of the class `RecursiveXmlVisitor` implement an XML visitor that will recursively
+ * visit all of the nodes in an XML structure. For example, using an instance of this class to visit
+ * a [XmlTagNode] will also cause all of the contained [XmlAttributeNode]s and
+ * [XmlTagNode]s to be visited.
+ *
+ * Subclasses that override a visit method must either invoke the overridden visit method or must
+ * explicitly ask the visited node to visit its children. Failure to do so will cause the children
+ * of the visited node to not be visited.
+ */
+class RecursiveXmlVisitor<R> implements XmlVisitor<R> {
+  @override
+  R visitHtmlScriptTagNode(HtmlScriptTagNode node) {
+    node.visitChildren(this);
+    return null;
+  }
+
+  @override
+  R visitHtmlUnit(HtmlUnit node) {
+    node.visitChildren(this);
+    return null;
+  }
+
+  @override
+  R visitXmlAttributeNode(XmlAttributeNode node) {
+    node.visitChildren(this);
+    return null;
+  }
+
+  @override
+  R visitXmlTagNode(XmlTagNode node) {
+    node.visitChildren(this);
+    return null;
+  }
+}
+
+/**
+ * Instances of the class `SimpleXmlVisitor` implement an AST visitor that will do nothing
+ * when visiting an AST node. It is intended to be a superclass for classes that use the visitor
+ * pattern primarily as a dispatch mechanism (and hence don't need to recursively visit a whole
+ * structure) and that only need to visit a small number of node types.
+ */
+class SimpleXmlVisitor<R> implements XmlVisitor<R> {
+  @override
+  R visitHtmlScriptTagNode(HtmlScriptTagNode node) => null;
+
+  @override
+  R visitHtmlUnit(HtmlUnit htmlUnit) => null;
+
+  @override
+  R visitXmlAttributeNode(XmlAttributeNode xmlAttributeNode) => null;
+
+  @override
+  R visitXmlTagNode(XmlTagNode xmlTagNode) => null;
+}
+
+/**
+ * Instances of the class `StringScanner` implement a scanner that reads from a string. The
+ * scanning logic is in the superclass.
+ */
+class StringScanner extends AbstractScanner {
+  /**
+   * The string from which characters will be read.
+   */
+  final String _string;
+
+  /**
+   * The number of characters in the string.
+   */
+  int _stringLength = 0;
+
+  /**
+   * The index, relative to the string, of the last character that was read.
+   */
+  int _charOffset = 0;
+
+  /**
+   * Initialize a newly created scanner to scan the characters in the given string.
+   *
+   * @param source the source being scanned
+   * @param string the string from which characters will be read
+   */
+  StringScanner(Source source, this._string) : super(source) {
+    this._stringLength = _string.length;
+    this._charOffset = -1;
+  }
+
+  @override
+  int get offset => _charOffset;
+
+  void set offset(int offset) {
+    _charOffset = offset;
+  }
+
+  @override
+  int advance() {
+    if (++_charOffset < _stringLength) {
+      return _string.codeUnitAt(_charOffset);
+    }
+    _charOffset = _stringLength;
+    return -1;
+  }
+
+  @override
+  String getString(int start, int endDelta) =>
+      _string.substring(start, _charOffset + 1 + endDelta).toString();
+
+  @override
+  int peek() {
+    if (_charOffset + 1 < _stringLength) {
+      return _string.codeUnitAt(_charOffset + 1);
+    }
+    return -1;
+  }
+}
+
+/**
+ * Instances of the class `Token` represent a token that was scanned from the input. Each
+ * token knows which token follows it, acting as the head of a linked list of tokens.
+ */
+class Token {
+  /**
+   * The offset from the beginning of the file to the first character in the token.
+   */
+  final int offset;
+
+  /**
+   * The previous token in the token stream.
+   */
+  Token previous;
+
+  /**
+   * The next token in the token stream.
+   */
+  Token _next;
+
+  /**
+   * The type of the token.
+   */
+  final TokenType type;
+
+  /**
+   * The lexeme represented by this token.
+   */
+  String _value;
+
+  /**
+   * Initialize a newly created token.
+   *
+   * @param type the token type (not `null`)
+   * @param offset the offset from the beginning of the file to the first character in the token
+   */
+  Token.con1(TokenType type, int offset) : this.con2(type, offset, type.lexeme);
+
+  /**
+   * Initialize a newly created token.
+   *
+   * @param type the token type (not `null`)
+   * @param offset the offset from the beginning of the file to the first character in the token
+   * @param value the lexeme represented by this token (not `null`)
+   */
+  Token.con2(this.type, this.offset, String value) {
+    this._value = StringUtilities.intern(value);
+  }
+
+  /**
+   * Return the offset from the beginning of the file to the character after last character of the
+   * token.
+   *
+   * @return the offset from the beginning of the file to the first character after last character
+   *         of the token
+   */
+  int get end => offset + length;
+
+  /**
+   * Return `true` if this token is a synthetic token. A synthetic token is a token that was
+   * introduced by the parser in order to recover from an error in the code. Synthetic tokens always
+   * have a length of zero (`0`).
+   *
+   * @return `true` if this token is a synthetic token
+   */
+  bool get isSynthetic => length == 0;
+
+  /**
+   * Return the number of characters in the node's source range.
+   *
+   * @return the number of characters in the node's source range
+   */
+  int get length => lexeme.length;
+
+  /**
+   * Return the lexeme that represents this token.
+   *
+   * @return the lexeme (not `null`)
+   */
+  String get lexeme => _value;
+
+  /**
+   * Return the next token in the token stream.
+   *
+   * @return the next token in the token stream
+   */
+  Token get next => _next;
+
+  /**
+   * Set the next token in the token stream to the given token. This has the side-effect of setting
+   * this token to be the previous token for the given token.
+   *
+   * @param token the next token in the token stream
+   * @return the token that was passed in
+   */
+  Token setNext(Token token) {
+    _next = token;
+    token.previous = this;
+    return token;
+  }
+
+  @override
+  String toString() => lexeme;
+}
+
+/**
+ * The enumeration `TokenType` defines the types of tokens that can be returned by the
+ * scanner.
+ */
+class TokenType extends Enum<TokenType> {
+  /**
+   * The type of the token that marks the end of the input.
+   */
+  static const TokenType EOF = const TokenType_EOF('EOF', 0, "");
+
+  static const TokenType EQ = const TokenType('EQ', 1, "=");
+
+  static const TokenType GT = const TokenType('GT', 2, ">");
+
+  static const TokenType LT_SLASH = const TokenType('LT_SLASH', 3, "</");
+
+  static const TokenType LT = const TokenType('LT', 4, "<");
+
+  static const TokenType SLASH_GT = const TokenType('SLASH_GT', 5, "/>");
+
+  static const TokenType COMMENT = const TokenType('COMMENT', 6, null);
+
+  static const TokenType DECLARATION = const TokenType('DECLARATION', 7, null);
+
+  static const TokenType DIRECTIVE = const TokenType('DIRECTIVE', 8, null);
+
+  static const TokenType STRING = const TokenType('STRING', 9, null);
+
+  static const TokenType TAG = const TokenType('TAG', 10, null);
+
+  static const TokenType TEXT = const TokenType('TEXT', 11, null);
+
+  static const List<TokenType> values = const [
+    EOF,
+    EQ,
+    GT,
+    LT_SLASH,
+    LT,
+    SLASH_GT,
+    COMMENT,
+    DECLARATION,
+    DIRECTIVE,
+    STRING,
+    TAG,
+    TEXT
+  ];
+
+  /**
+   * The lexeme that defines this type of token, or `null` if there is more than one possible
+   * lexeme for this type of token.
+   */
+  final String lexeme;
+
+  const TokenType(String name, int ordinal, this.lexeme) : super(name, ordinal);
+}
+
+class TokenType_EOF extends TokenType {
+  const TokenType_EOF(String name, int ordinal, String arg0)
+      : super(name, ordinal, arg0);
+
+  @override
+  String toString() => "-eof-";
+}
+
+/**
+ * Instances of the class `ToSourceVisitor` write a source representation of a visited XML
+ * node (and all of it's children) to a writer.
+ */
+class ToSourceVisitor implements XmlVisitor<Object> {
+  /**
+   * The writer to which the source is to be written.
+   */
+  final PrintWriter _writer;
+
+  /**
+   * Initialize a newly created visitor to write source code representing the visited nodes to the
+   * given writer.
+   *
+   * @param writer the writer to which the source is to be written
+   */
+  ToSourceVisitor(this._writer);
+
+  @override
+  Object visitHtmlScriptTagNode(HtmlScriptTagNode node) =>
+      visitXmlTagNode(node);
+
+  @override
+  Object visitHtmlUnit(HtmlUnit node) {
+    for (XmlTagNode child in node.tagNodes) {
+      _visit(child);
+    }
+    return null;
+  }
+
+  @override
+  Object visitXmlAttributeNode(XmlAttributeNode node) {
+    String name = node.name;
+    Token value = node.valueToken;
+    if (name.length == 0) {
+      _writer.print("__");
+    } else {
+      _writer.print(name);
+    }
+    _writer.print("=");
+    if (value == null) {
+      _writer.print("__");
+    } else {
+      _writer.print(value.lexeme);
+    }
+    return null;
+  }
+
+  @override
+  Object visitXmlTagNode(XmlTagNode node) {
+    _writer.print("<");
+    String tagName = node.tag;
+    _writer.print(tagName);
+    for (XmlAttributeNode attribute in node.attributes) {
+      _writer.print(" ");
+      _visit(attribute);
+    }
+    _writer.print(node.attributeEnd.lexeme);
+    if (node.closingTag != null) {
+      for (XmlTagNode child in node.tagNodes) {
+        _visit(child);
+      }
+      _writer.print("</");
+      _writer.print(tagName);
+      _writer.print(">");
+    }
+    return null;
+  }
+
+  /**
+   * Safely visit the given node.
+   *
+   * @param node the node to be visited
+   */
+  void _visit(XmlNode node) {
+    if (node != null) {
+      node.accept(this);
+    }
+  }
+}
+
+/**
+ * Instances of `XmlAttributeNode` represent name/value pairs owned by an [XmlTagNode].
+ */
+class XmlAttributeNode extends XmlNode {
+  /**
+   * An empty list of XML attribute nodes.
+   */
+  static const List<XmlAttributeNode> EMPTY_LIST = const <XmlAttributeNode>[];
+
+  final Token _name;
+
+  final Token equals;
+
+  final Token _value;
+
+  List<XmlExpression> expressions = XmlExpression.EMPTY_ARRAY;
+
+  /**
+   * Construct a new instance representing an XML attribute.
+   *
+   * @param name the name token (not `null`). This may be a zero length token if the attribute
+   *          is badly formed.
+   * @param equals the equals sign or `null` if none
+   * @param value the value token (not `null`)
+   */
+  XmlAttributeNode(this._name, this.equals, this._value);
+
+  @override
+  Token get beginToken => _name;
+
+  @override
+  Token get endToken => _value;
+
+  /**
+   * Answer the attribute name. This may be a zero length string if the attribute is badly formed.
+   *
+   * @return the name (not `null`)
+   */
+  String get name => _name.lexeme;
+
+  /**
+   * Answer the attribute name token. This may be a zero length token if the attribute is badly
+   * formed.
+   *
+   * @return the name token (not `null`)
+   */
+  Token get nameToken => _name;
+
+  /**
+   * Answer the lexeme for the value token without the leading and trailing quotes.
+   *
+   * @return the text or `null` if the value is not specified
+   */
+  String get text {
+    if (_value == null) {
+      return null;
+    }
+    //TODO (danrubel): replace HTML character encodings with the actual
+    // characters
+    String text = _value.lexeme;
+    int len = text.length;
+    if (len > 0) {
+      if (text.codeUnitAt(0) == 0x22) {
+        if (len > 1 && text.codeUnitAt(len - 1) == 0x22) {
+          return text.substring(1, len - 1);
+        } else {
+          return text.substring(1);
+        }
+      } else if (text.codeUnitAt(0) == 0x27) {
+        if (len > 1 && text.codeUnitAt(len - 1) == 0x27) {
+          return text.substring(1, len - 1);
+        } else {
+          return text.substring(1);
+        }
+      }
+    }
+    return text;
+  }
+
+  /**
+   * Answer the offset of the value after the leading quote.
+   *
+   * @return the offset of the value, or `-1` if the value is not specified
+   */
+  int get textOffset {
+    if (_value == null) {
+      return -1;
+    }
+    String text = _value.lexeme;
+    if (StringUtilities.startsWithChar(text, 0x22) ||
+        StringUtilities.startsWithChar(text, 0x27)) {
+      return _value.offset + 1;
+    }
+    return _value.offset;
+  }
+
+  /**
+   * Answer the attribute value token. A properly formed value will start and end with matching
+   * quote characters, but the value returned may not be properly formed.
+   *
+   * @return the value token or `null` if this represents a badly formed attribute
+   */
+  Token get valueToken => _value;
+
+  @override
+  accept(XmlVisitor visitor) => visitor.visitXmlAttributeNode(this);
+
+  @override
+  void visitChildren(XmlVisitor visitor) {
+    // no children to visit
+  }
+}
+
+/**
+ * Instances of the class `XmlExpression` represent an abstract expression embedded into
+ * [XmlNode].
+ */
+abstract class XmlExpression {
+  /**
+   * An empty list of expressions.
+   */
+  static const List<XmlExpression> EMPTY_ARRAY = const <XmlExpression>[];
+
+  /**
+   * Return the offset of the character immediately following the last character of this
+   * expression's source range. This is equivalent to `getOffset() + getLength()`.
+   *
+   * @return the offset of the character just past the expression's source range
+   */
+  int get end;
+
+  /**
+   * Return the number of characters in the expression's source range.
+   */
+  int get length;
+
+  /**
+   * Return the offset of the first character in the expression's source range.
+   */
+  int get offset;
+
+  /**
+   * Check if the given offset belongs to the expression's source range.
+   */
+  bool contains(int offset) => this.offset <= offset && offset < end;
+
+  /**
+   * Return the [Reference] at the given offset.
+   *
+   * @param offset the offset from the beginning of the file
+   * @return the [Reference] at the given offset, maybe `null`
+   */
+  XmlExpression_Reference getReference(int offset);
+}
+
+/**
+ * The reference to the [Element].
+ */
+class XmlExpression_Reference {
+  Element element;
+
+  int offset = 0;
+
+  int length = 0;
+
+  XmlExpression_Reference(this.element, this.offset, this.length);
+}
+
+/**
+ * The abstract class `XmlNode` defines behavior common to all XML/HTML nodes.
+ */
+abstract class XmlNode {
+  /**
+   * The parent of the node, or `null` if the node is the root of an AST structure.
+   */
+  XmlNode _parent;
+
+  /**
+   * The element associated with this node or `null` if the receiver is not resolved.
+   */
+  Element _element;
+
+  /**
+   * Return the first token included in this node's source range.
+   *
+   * @return the first token or `null` if none
+   */
+  Token get beginToken;
+
+  /**
+   * Return the element associated with this node.
+   *
+   * @return the element or `null` if the receiver is not resolved
+   */
+  Element get element => _element;
+
+  /**
+   * Set the element associated with this node.
+   *
+   * @param element the element
+   */
+  void set element(Element element) {
+    this._element = element;
+  }
+
+  /**
+   * Return the offset of the character immediately following the last character of this node's
+   * source range. This is equivalent to `node.getOffset() + node.getLength()`. For an html
+   * unit this will be equal to the length of the unit's source.
+   *
+   * @return the offset of the character just past the node's source range
+   */
+  int get end => offset + length;
+
+  /**
+   * Return the last token included in this node's source range.
+   *
+   * @return the last token or `null` if none
+   */
+  Token get endToken;
+
+  /**
+   * Return the number of characters in the node's source range.
+   *
+   * @return the number of characters in the node's source range
+   */
+  int get length {
+    Token beginToken = this.beginToken;
+    Token endToken = this.endToken;
+    if (beginToken == null || endToken == null) {
+      return -1;
+    }
+    return endToken.offset + endToken.length - beginToken.offset;
+  }
+
+  /**
+   * Return the offset from the beginning of the file to the first character in the node's source
+   * range.
+   *
+   * @return the offset from the beginning of the file to the first character in the node's source
+   *         range
+   */
+  int get offset {
+    Token beginToken = this.beginToken;
+    if (beginToken == null) {
+      return -1;
+    }
+    return this.beginToken.offset;
+  }
+
+  /**
+   * Return this node's parent node, or `null` if this node is the root of an AST structure.
+   *
+   * Note that the relationship between an AST node and its parent node may change over the lifetime
+   * of a node.
+   *
+   * @return the parent of this node, or `null` if none
+   */
+  XmlNode get parent => _parent;
+
+  /**
+   * Set the parent of this node to the given node.
+   *
+   * @param newParent the node that is to be made the parent of this node
+   */
+  void set parent(XmlNode newParent) {
+    XmlNode current = newParent;
+    while (current != null) {
+      if (identical(current, this)) {
+        AnalysisEngine.instance.logger.logError(
+            "Circular structure while setting an XML node's parent",
+            new CaughtException(
+                new ArgumentError(_buildRecursiveStructureMessage(newParent)),
+                null));
+        return;
+      }
+      current = current.parent;
+    }
+    _parent = newParent;
+  }
+
+  /**
+   * Use the given visitor to visit this node.
+   *
+   * @param visitor the visitor that will visit this node
+   * @return the value returned by the visitor as a result of visiting this node
+   */
+  accept(XmlVisitor visitor);
+
+  /**
+   * Make this node the parent of the given child node.
+   *
+   * @param child the node that will become a child of this node
+   * @return the node that was made a child of this node
+   */
+  XmlNode becomeParentOf(XmlNode child) {
+    if (child != null) {
+      XmlNode node = child;
+      node.parent = this;
+    }
+    return child;
+  }
+
+  /**
+   * Make this node the parent of the given child nodes.
+   *
+   * @param children the nodes that will become the children of this node
+   * @param ifEmpty the (empty) nodes to return if "children" is empty
+   * @return the nodes that were made children of this node
+   */
+  List becomeParentOfAll(List children, {List ifEmpty}) {
+    if (children == null || children.isEmpty) {
+      if (ifEmpty != null) {
+        return ifEmpty;
+      }
+    }
+    if (children != null) {
+      children.forEach((XmlNode node) {
+        node.parent = this;
+      });
+    }
+    return children;
+  }
+
+  @override
+  String toString() {
+    PrintStringWriter writer = new PrintStringWriter();
+    accept(new ToSourceVisitor(writer));
+    return writer.toString();
+  }
+
+  /**
+   * Use the given visitor to visit all of the children of this node. The children will be visited
+   * in source order.
+   *
+   * @param visitor the visitor that will be used to visit the children of this node
+   */
+  void visitChildren(XmlVisitor visitor);
+
+  /**
+   * This method exists for debugging purposes only.
+   */
+  void _appendIdentifier(StringBuffer buffer, XmlNode node) {
+    if (node is XmlTagNode) {
+      buffer.write(node.tag);
+    } else if (node is XmlAttributeNode) {
+      buffer.write(node.name);
+    } else {
+      buffer.write("htmlUnit");
+    }
+  }
+
+  /**
+   * This method exists for debugging purposes only.
+   */
+  String _buildRecursiveStructureMessage(XmlNode newParent) {
+    StringBuffer buffer = new StringBuffer();
+    buffer.write("Attempt to create recursive structure: ");
+    XmlNode current = newParent;
+    while (current != null) {
+      if (!identical(current, newParent)) {
+        buffer.write(" -> ");
+      }
+      if (identical(current, this)) {
+        buffer.writeCharCode(0x2A);
+        _appendIdentifier(buffer, current);
+        buffer.writeCharCode(0x2A);
+      } else {
+        _appendIdentifier(buffer, current);
+      }
+      current = current.parent;
+    }
+    return buffer.toString();
+  }
+}
+
+/**
+ * Instances of the class `XmlParser` are used to parse tokens into a AST structure comprised
+ * of [XmlNode]s.
+ */
+class XmlParser {
+  /**
+   * The source being parsed.
+   */
+  final Source source;
+
+  /**
+   * The next token to be parsed.
+   */
+  Token _currentToken;
+
+  /**
+   * Construct a parser for the specified source.
+   *
+   * @param source the source being parsed
+   */
+  XmlParser(this.source);
+
+  /**
+   * Answer the current token.
+   *
+   * @return the current token
+   */
+  Token get currentToken => _currentToken;
+
+  /**
+   * Create a node representing an attribute.
+   *
+   * @param name the name of the attribute
+   * @param equals the equals sign, or `null` if there is no value
+   * @param value the value of the attribute
+   * @return the node that was created
+   */
+  XmlAttributeNode createAttributeNode(Token name, Token equals, Token value) =>
+      new XmlAttributeNode(name, equals, value);
+
+  /**
+   * Create a node representing a tag.
+   *
+   * @param nodeStart the token marking the beginning of the tag
+   * @param tag the name of the tag
+   * @param attributes the attributes in the tag
+   * @param attributeEnd the token terminating the region where attributes can be
+   * @param tagNodes the children of the tag
+   * @param contentEnd the token that starts the closing tag
+   * @param closingTag the name of the tag that occurs in the closing tag
+   * @param nodeEnd the last token in the tag
+   * @return the node that was created
+   */
+  XmlTagNode createTagNode(Token nodeStart, Token tag,
+      List<XmlAttributeNode> attributes, Token attributeEnd,
+      List<XmlTagNode> tagNodes, Token contentEnd, Token closingTag,
+      Token nodeEnd) => new XmlTagNode(nodeStart, tag, attributes, attributeEnd,
+      tagNodes, contentEnd, closingTag, nodeEnd);
+
+  /**
+   * Answer `true` if the specified tag is self closing and thus should never have content or
+   * child tag nodes.
+   *
+   * @param tag the tag (not `null`)
+   * @return `true` if self closing
+   */
+  bool isSelfClosing(Token tag) => false;
+
+  /**
+   * Parse the entire token stream and in the process, advance the current token to the end of the
+   * token stream.
+   *
+   * @return the list of tag nodes found (not `null`, contains no `null`)
+   */
+  List<XmlTagNode> parseTopTagNodes(Token firstToken) {
+    _currentToken = firstToken;
+    List<XmlTagNode> tagNodes = new List<XmlTagNode>();
+    TokenType type = _currentToken.type;
+    while (type != TokenType.EOF) {
+      if (type == TokenType.LT) {
+        tagNodes.add(_parseTagNode());
+      } else if (type == TokenType.DECLARATION ||
+          type == TokenType.DIRECTIVE ||
+          type == TokenType.COMMENT) {
+        // ignored tokens
+        _currentToken = _currentToken.next;
+      } else {
+        _reportUnexpectedToken();
+        _currentToken = _currentToken.next;
+      }
+      type = _currentToken.type;
+    }
+    return tagNodes;
+  }
+
+  /**
+   * Insert a synthetic token of the specified type before the current token
+   *
+   * @param type the type of token to be inserted (not `null`)
+   * @return the synthetic token that was inserted (not `null`)
+   */
+  Token _insertSyntheticToken(TokenType type) {
+    Token token = new Token.con2(type, _currentToken.offset, "");
+    _currentToken.previous.setNext(token);
+    token.setNext(_currentToken);
+    return token;
+  }
+
+  /**
+   * Parse the token stream for an attribute. This method advances the current token over the
+   * attribute, but should not be called if the [currentToken] is not [TokenType.TAG].
+   *
+   * @return the attribute (not `null`)
+   */
+  XmlAttributeNode _parseAttribute() {
+    // Assume the current token is a tag
+    Token name = _currentToken;
+    _currentToken = _currentToken.next;
+    // Equals sign
+    Token equals;
+    if (_currentToken.type == TokenType.EQ) {
+      equals = _currentToken;
+      _currentToken = _currentToken.next;
+    } else {
+      _reportUnexpectedToken();
+      equals = _insertSyntheticToken(TokenType.EQ);
+    }
+    // String value
+    Token value;
+    if (_currentToken.type == TokenType.STRING) {
+      value = _currentToken;
+      _currentToken = _currentToken.next;
+    } else {
+      _reportUnexpectedToken();
+      value = _insertSyntheticToken(TokenType.STRING);
+    }
+    return createAttributeNode(name, equals, value);
+  }
+
+  /**
+   * Parse the stream for a sequence of attributes. This method advances the current token to the
+   * next [TokenType.GT], [TokenType.SLASH_GT], or [TokenType.EOF].
+   *
+   * @return a collection of zero or more attributes (not `null`, contains no `null`s)
+   */
+  List<XmlAttributeNode> _parseAttributes() {
+    TokenType type = _currentToken.type;
+    if (type == TokenType.GT ||
+        type == TokenType.SLASH_GT ||
+        type == TokenType.EOF) {
+      return XmlTagNode.NO_ATTRIBUTES;
+    }
+    List<XmlAttributeNode> attributes = new List<XmlAttributeNode>();
+    while (type != TokenType.GT &&
+        type != TokenType.SLASH_GT &&
+        type != TokenType.EOF) {
+      if (type == TokenType.TAG) {
+        attributes.add(_parseAttribute());
+      } else {
+        _reportUnexpectedToken();
+        _currentToken = _currentToken.next;
+      }
+      type = _currentToken.type;
+    }
+    return attributes;
+  }
+
+  /**
+   * Parse the stream for a sequence of tag nodes existing within a parent tag node. This method
+   * advances the current token to the next [TokenType.LT_SLASH] or [TokenType.EOF].
+   *
+   * @return a list of nodes (not `null`, contains no `null`s)
+   */
+  List<XmlTagNode> _parseChildTagNodes() {
+    TokenType type = _currentToken.type;
+    if (type == TokenType.LT_SLASH || type == TokenType.EOF) {
+      return XmlTagNode.NO_TAG_NODES;
+    }
+    List<XmlTagNode> nodes = new List<XmlTagNode>();
+    while (type != TokenType.LT_SLASH && type != TokenType.EOF) {
+      if (type == TokenType.LT) {
+        nodes.add(_parseTagNode());
+      } else if (type == TokenType.COMMENT) {
+        // ignored token
+        _currentToken = _currentToken.next;
+      } else {
+        _reportUnexpectedToken();
+        _currentToken = _currentToken.next;
+      }
+      type = _currentToken.type;
+    }
+    return nodes;
+  }
+
+  /**
+   * Parse the token stream for the next tag node. This method advances current token over the
+   * parsed tag node, but should only be called if the current token is [TokenType.LT]
+   *
+   * @return the tag node or `null` if none found
+   */
+  XmlTagNode _parseTagNode() {
+    // Assume that the current node is a tag node start TokenType.LT
+    Token nodeStart = _currentToken;
+    _currentToken = _currentToken.next;
+    // Get the tag or create a synthetic tag and report an error
+    Token tag;
+    if (_currentToken.type == TokenType.TAG) {
+      tag = _currentToken;
+      _currentToken = _currentToken.next;
+    } else {
+      _reportUnexpectedToken();
+      tag = _insertSyntheticToken(TokenType.TAG);
+    }
+    // Parse the attributes
+    List<XmlAttributeNode> attributes = _parseAttributes();
+    // Token ending attribute list
+    Token attributeEnd;
+    if (_currentToken.type == TokenType.GT ||
+        _currentToken.type == TokenType.SLASH_GT) {
+      attributeEnd = _currentToken;
+      _currentToken = _currentToken.next;
+    } else {
+      _reportUnexpectedToken();
+      attributeEnd = _insertSyntheticToken(TokenType.SLASH_GT);
+    }
+    // If the node has no children, then return the node
+    if (attributeEnd.type == TokenType.SLASH_GT || isSelfClosing(tag)) {
+      return createTagNode(nodeStart, tag, attributes, attributeEnd,
+          XmlTagNode.NO_TAG_NODES, _currentToken, null, attributeEnd);
+    }
+    // Parse the child tag nodes
+    List<XmlTagNode> tagNodes = _parseChildTagNodes();
+    // Token ending child tag nodes
+    Token contentEnd;
+    if (_currentToken.type == TokenType.LT_SLASH) {
+      contentEnd = _currentToken;
+      _currentToken = _currentToken.next;
+    } else {
+      // TODO (danrubel): handle self closing HTML elements by inserting
+      // synthetic tokens but not reporting an error
+      _reportUnexpectedToken();
+      contentEnd = _insertSyntheticToken(TokenType.LT_SLASH);
+    }
+    // Closing tag
+    Token closingTag;
+    if (_currentToken.type == TokenType.TAG) {
+      closingTag = _currentToken;
+      _currentToken = _currentToken.next;
+    } else {
+      _reportUnexpectedToken();
+      closingTag = _insertSyntheticToken(TokenType.TAG);
+    }
+    // Token ending node
+    Token nodeEnd;
+    if (_currentToken.type == TokenType.GT) {
+      nodeEnd = _currentToken;
+      _currentToken = _currentToken.next;
+    } else {
+      _reportUnexpectedToken();
+      nodeEnd = _insertSyntheticToken(TokenType.GT);
+    }
+    return createTagNode(nodeStart, tag, attributes, attributeEnd, tagNodes,
+        contentEnd, closingTag, nodeEnd);
+  }
+
+  /**
+   * Report the current token as unexpected
+   */
+  void _reportUnexpectedToken() {
+    // TODO (danrubel): report unexpected token
+  }
+}
+
+/**
+ * Instances of `XmlTagNode` represent XML or HTML elements such as `` and
+ * `<body foo="bar"> ... </body>`.
+ */
+class XmlTagNode extends XmlNode {
+  /**
+   * Constant representing empty list of attributes.
+   */
+  static List<XmlAttributeNode> NO_ATTRIBUTES =
+      new UnmodifiableListView(new List<XmlAttributeNode>());
+
+  /**
+   * Constant representing empty list of tag nodes.
+   */
+  static List<XmlTagNode> NO_TAG_NODES =
+      new UnmodifiableListView(new List<XmlTagNode>());
+
+  /**
+   * The starting [TokenType.LT] token (not `null`).
+   */
+  final Token nodeStart;
+
+  /**
+   * The [TokenType.TAG] token after the starting '&lt;' (not `null`).
+   */
+  final Token _tag;
+
+  /**
+   * The attributes contained by the receiver (not `null`, contains no `null`s).
+   */
+  List<XmlAttributeNode> _attributes;
+
+  /**
+   * The [TokenType.GT] or [TokenType.SLASH_GT] token after the attributes (not
+   * `null`). The token may be the same token as [nodeEnd] if there are no child
+   * [tagNodes].
+   */
+  final Token attributeEnd;
+
+  /**
+   * The tag nodes contained in the receiver (not `null`, contains no `null`s).
+   */
+  List<XmlTagNode> _tagNodes;
+
+  /**
+   * The token (not `null`) after the content, which may be
+   * * (1) [TokenType.LT_SLASH] for nodes with open and close tags, or
+   * * (2) the [TokenType.LT] nodeStart of the next sibling node if this node is self
+   * closing or the attributeEnd is [TokenType.SLASH_GT], or
+   * * (3) [TokenType.EOF] if the node does not have a closing tag and is the last node in
+   * the stream [TokenType.LT_SLASH] token after the content, or `null` if there is no
+   * content and the attributes ended with [TokenType.SLASH_GT].
+   */
+  final Token contentEnd;
+
+  /**
+   * The closing [TokenType.TAG] after the child elements or `null` if there is no
+   * content and the attributes ended with [TokenType.SLASH_GT]
+   */
+  final Token closingTag;
+
+  /**
+   * The ending [TokenType.GT] or [TokenType.SLASH_GT] token (not `null`).
+   */
+  final Token nodeEnd;
+
+  /**
+   * The expressions that are embedded in the tag's content.
+   */
+  List<XmlExpression> expressions = XmlExpression.EMPTY_ARRAY;
+
+  /**
+   * Construct a new instance representing an XML or HTML element
+   *
+   * @param nodeStart the starting [TokenType.LT] token (not `null`)
+   * @param tag the [TokenType.TAG] token after the starting '&lt;' (not `null`).
+   * @param attributes the attributes associated with this element or [NO_ATTRIBUTES] (not
+   *          `null`, contains no `null`s)
+   * @param attributeEnd The [TokenType.GT] or [TokenType.SLASH_GT] token after the
+   *          attributes (not `null`). The token may be the same token as [nodeEnd] if
+   *          there are no child [tagNodes].
+   * @param tagNodes child tag nodes of the receiver or [NO_TAG_NODES] (not `null`,
+   *          contains no `null`s)
+   * @param contentEnd the token (not `null`) after the content, which may be
+   *          * (1) [TokenType.LT_SLASH] for nodes with open and close tags, or
+   *          * (2) the [TokenType.LT] nodeStart of the next sibling node if this node is
+   *          self closing or the attributeEnd is [TokenType.SLASH_GT], or
+   *          * (3) [TokenType.EOF] if the node does not have a closing tag and is the last
+   *          node in the stream [TokenType.LT_SLASH] token after the content, or `null`
+   *          if there is no content and the attributes ended with [TokenType.SLASH_GT].
+   * @param closingTag the closing [TokenType.TAG] after the child elements or `null` if
+   *          there is no content and the attributes ended with [TokenType.SLASH_GT]
+   * @param nodeEnd the ending [TokenType.GT] or [TokenType.SLASH_GT] token (not
+   *          `null`)
+   */
+  XmlTagNode(this.nodeStart, this._tag, List<XmlAttributeNode> attributes,
+      this.attributeEnd, List<XmlTagNode> tagNodes, this.contentEnd,
+      this.closingTag, this.nodeEnd) {
+    this._attributes = becomeParentOfAll(attributes, ifEmpty: NO_ATTRIBUTES);
+    this._tagNodes = becomeParentOfAll(tagNodes, ifEmpty: NO_TAG_NODES);
+  }
+
+  /**
+   * Answer the receiver's attributes. Callers should not manipulate the returned list to edit the
+   * AST structure.
+   *
+   * @return the attributes (not `null`, contains no `null`s)
+   */
+  List<XmlAttributeNode> get attributes => _attributes;
+
+  @override
+  Token get beginToken => nodeStart;
+
+  /**
+   * Return a string representing the content contained in the receiver. This
+   * includes the textual representation of any child tag nodes ([getTagNodes]).
+   * Whitespace between '&lt;', '&lt;/', and '>', '/>' is discarded, but all
+   * other whitespace is preserved.
+   */
+  String get content {
+    Token token = attributeEnd.next;
+    if (identical(token, contentEnd)) {
+      return "";
+    }
+    // TODO(danrubel) Handle CDATA and replace HTML character encodings with
+    // the actual characters.
+    String content = token.lexeme;
+    token = token.next;
+    if (identical(token, contentEnd)) {
+      return content;
+    }
+    StringBuffer buffer = new StringBuffer();
+    buffer.write(content);
+    while (!identical(token, contentEnd)) {
+      buffer.write(token.lexeme);
+      token = token.next;
+    }
+    return buffer.toString();
+  }
+
+  @override
+  Token get endToken {
+    if (nodeEnd != null) {
+      return nodeEnd;
+    }
+    if (closingTag != null) {
+      return closingTag;
+    }
+    if (contentEnd != null) {
+      return contentEnd;
+    }
+    if (!_tagNodes.isEmpty) {
+      return _tagNodes[_tagNodes.length - 1].endToken;
+    }
+    if (attributeEnd != null) {
+      return attributeEnd;
+    }
+    if (!_attributes.isEmpty) {
+      return _attributes[_attributes.length - 1].endToken;
+    }
+    return _tag;
+  }
+
+  /**
+   * Answer the tag name after the starting '&lt;'.
+   *
+   * @return the tag name (not `null`)
+   */
+  String get tag => _tag.lexeme;
+
+  /**
+   * Answer the tag nodes contained in the receiver. Callers should not manipulate the returned list
+   * to edit the AST structure.
+   *
+   * @return the children (not `null`, contains no `null`s)
+   */
+  List<XmlTagNode> get tagNodes => _tagNodes;
+
+  /**
+   * Answer the [TokenType.TAG] token after the starting '&lt;'.
+   *
+   * @return the token (not `null`)
+   */
+  Token get tagToken => _tag;
+
+  @override
+  accept(XmlVisitor visitor) => visitor.visitXmlTagNode(this);
+
+  /**
+   * Answer the attribute with the specified name.
+   *
+   * @param name the attribute name
+   * @return the attribute or `null` if no matching attribute is found
+   */
+  XmlAttributeNode getAttribute(String name) {
+    for (XmlAttributeNode attribute in _attributes) {
+      if (attribute.name == name) {
+        return attribute;
+      }
+    }
+    return null;
+  }
+
+  /**
+   * Find the attribute with the given name (see [getAttribute] and answer the lexeme
+   * for the attribute's value token without the leading and trailing quotes (see
+   * [XmlAttributeNode.getText]).
+   *
+   * @param name the attribute name
+   * @return the attribute text or `null` if no matching attribute is found
+   */
+  String getAttributeText(String name) {
+    XmlAttributeNode attribute = getAttribute(name);
+    return attribute != null ? attribute.text : null;
+  }
+
+  @override
+  void visitChildren(XmlVisitor visitor) {
+    for (XmlAttributeNode node in _attributes) {
+      node.accept(visitor);
+    }
+    for (XmlTagNode node in _tagNodes) {
+      node.accept(visitor);
+    }
+  }
+}
+
+/**
+ * The interface `XmlVisitor` defines the behavior of objects that can be used to visit an
+ * [XmlNode] structure.
+ */
+abstract class XmlVisitor<R> {
+  R visitHtmlScriptTagNode(HtmlScriptTagNode node);
+
+  R visitHtmlUnit(HtmlUnit htmlUnit);
+
+  R visitXmlAttributeNode(XmlAttributeNode xmlAttributeNode);
+
+  R visitXmlTagNode(XmlTagNode xmlTagNode);
+}