move csslib into dart svn

pkg/csslib/lib/parser.dart

+// Copyright (c) 2012, 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 csslib.parser;
+
+import 'dart:math' as math;
+
+import 'package:source_maps/span.dart' show SourceFile, Span, FileSpan;
+
+import "visitor.dart";
+import 'src/messages.dart';
+import 'src/options.dart';
+
+part 'src/analyzer.dart';
+part 'src/property.dart';
+part 'src/token.dart';
+part 'src/tokenizer_base.dart';
+part 'src/tokenizer.dart';
+part 'src/tokenkind.dart';
+
+
+/** Used for parser lookup ahead (used for nested selectors Less support). */
+class ParserState extends TokenizerState {
+  final Token peekToken;
+  final Token previousToken;
+
+  ParserState(this.peekToken, this.previousToken, Tokenizer tokenizer)
+      : super(tokenizer);
+}
+
+void _createMessages({List errors, List options}) {
+  if (errors == null) errors = [];
+
+  if (options == null) {
+    options = ['--no-colors', 'memory'];
+  }
+  var opt = PreprocessorOptions.parse(options);
+  messages = new Messages(options: opt, printHandler: errors.add);
+}
+
+/** CSS checked mode enabled. */
+bool get isChecked => messages.options.checked;
+
+// TODO(terry): Remove nested name parameter.
+/** Parse and analyze the CSS file. */
+StyleSheet compile(var input, {List errors, List options, bool nested: true}) {
+  var source = _inputAsString(input);
+
+  _createMessages(errors: errors, options: options);
+
+  var file = new SourceFile.text(null, source);
+
+  var tree = new Parser(file, source).parse();
+
+  analyze([tree], errors: errors, options: options);
+
+  return tree;
+}
+
+/** Analyze the CSS file. */
+void analyze(List<StyleSheet> styleSheets,  {List errors, List options}) {
+  _createMessages(errors: errors, options: options);
+  new Analyzer(styleSheets, messages).run();
+}
+
+/**
+ * Parse the [input] CSS stylesheet into a tree. The [input] can be a [String],
+ * or [List<int>] of bytes and returns a [StyleSheet] AST.  The optional
+ * [errors] list will contain each error/warning as a [Message].
+ */
+StyleSheet parse(var input, {List errors, List options}) {
+  var source = _inputAsString(input);
+
+  _createMessages(errors: errors, options: options);
+
+  var file = new SourceFile.text(null, source);
+
+  return new Parser(file, source).parse();
+}
+
+/**
+ * Parse the [input] CSS selector into a tree. The [input] can be a [String],
+ * or [List<int>] of bytes and returns a [StyleSheet] AST.  The optional
+ * [errors] list will contain each error/warning as a [Message].
+ */
+StyleSheet selector(var input, {List errors}) {
+  var source = _inputAsString(input);
+
+  _createMessages(errors: errors);
+
+  var file = new SourceFile.text(null, source);
+
+  return new Parser(file, source).parseSelector();
+}
+
+String _inputAsString(var input) {
+  String source;
+
+  if (input is String) {
+    source = input;
+  } else if (input is List<int>) {
+    // TODO(terry): The parse function needs an "encoding" argument and will
+    //              default to whatever encoding CSS defaults to.
+    //
+    // Here's some info about CSS encodings:
+    // http://www.w3.org/International/questions/qa-css-charset.en.php
+    //
+    // As JMesserly suggests it will probably need a "preparser" html5lib
+    // (encoding_parser.dart) that interprets the bytes as ASCII and scans for
+    // @charset. But for now an "encoding" argument would work.  Often the
+    // HTTP header will indicate the correct encoding.
+    //
+    // See encoding helpers at: package:html5lib/lib/src/char_encodings.dart
+    // These helpers can decode in different formats given an encoding name
+    // (mostly unicode, ascii, windows-1252 which is html5 default encoding).
+    source = new String.fromCharCodes(input);
+  } else {
+    // TODO(terry): Support RandomAccessFile using console.
+    throw new ArgumentError("'source' must be a String or "
+        "List<int> (of bytes). RandomAccessFile not supported from this "
+        "simple interface");
+  }
+
+  return source;
+}
+
+/** A simple recursive descent parser for CSS. */
+class Parser {
+  Tokenizer tokenizer;
+
+  /** Base url of CSS file. */
+  final String _baseUrl;
+
+  /**
+   * File containing the source being parsed, used to report errors with
+   * source-span locations.
+   */
+  final SourceFile file;
+
+  Token _previousToken;
+  Token _peekToken;
+
+  Parser(SourceFile file, String text, {int start: 0, String baseUrl})
+      : this.file = file,
+        _baseUrl = baseUrl,
+        tokenizer = new Tokenizer(file, text, true, start) {
+    _peekToken = tokenizer.next();
+  }
+
+  /** Main entry point for parsing an entire CSS file. */
+  StyleSheet parse() {
+    List<TreeNode> productions = [];
+
+    int start = _peekToken.start;
+    while (!_maybeEat(TokenKind.END_OF_FILE) && !_peekKind(TokenKind.RBRACE)) {
+      // TODO(terry): Need to handle charset.
+      var directive = processDirective();
+      if (directive != null) {
+        productions.add(directive);
+        _maybeEat(TokenKind.SEMICOLON);
+      } else {
+        RuleSet ruleset = processRuleSet();
+        if (ruleset != null) {
+          productions.add(ruleset);
+        } else {
+          break;
+        }
+      }
+    }
+
+    checkEndOfFile();
+
+    return new StyleSheet(productions, _makeSpan(start));
+  }
+
+  /** Main entry point for parsing a simple selector sequence. */
+  StyleSheet parseSelector() {
+    List<TreeNode> productions = [];
+
+    int start = _peekToken.start;
+    while (!_maybeEat(TokenKind.END_OF_FILE) && !_peekKind(TokenKind.RBRACE)) {
+      var selector = processSelector();
+      if (selector != null) {
+        productions.add(selector);
+      }
+    }
+
+    checkEndOfFile();
+
+    return new StyleSheet.selector(productions, _makeSpan(start));
+  }
+
+  /** Generate an error if [file] has not been completely consumed. */
+  void checkEndOfFile() {
+    if (!(_peekKind(TokenKind.END_OF_FILE) ||
+        _peekKind(TokenKind.INCOMPLETE_COMMENT))) {
+      _error('premature end of file unknown CSS', _peekToken.span);
+    }
+  }
+
+  /** Guard to break out of parser when an unexpected end of file is found. */
+  // TODO(jimhug): Failure to call this method can lead to inifinite parser
+  //   loops.  Consider embracing exceptions for more errors to reduce
+  //   the danger here.
+  bool isPrematureEndOfFile() {
+    if (_maybeEat(TokenKind.END_OF_FILE)) {
+      _error('unexpected end of file', _peekToken.span);
+      return true;
+    } else {
+      return false;
+    }
+  }
+
+  ///////////////////////////////////////////////////////////////////
+  // Basic support methods
+  ///////////////////////////////////////////////////////////////////
+  int _peek() {
+    return _peekToken.kind;
+  }
+
+  Token _next({unicodeRange : false}) {
+    _previousToken = _peekToken;
+    _peekToken = tokenizer.next(unicodeRange: unicodeRange);
+    return _previousToken;
+  }
+
+  bool _peekKind(int kind) {
+    return _peekToken.kind == kind;
+  }
+
+  /* Is the next token a legal identifier?  This includes pseudo-keywords. */
+  bool _peekIdentifier() {
+    return TokenKind.isIdentifier(_peekToken.kind);
+  }
+
+  /** Marks the parser/tokenizer look ahead to support Less nested selectors. */
+  ParserState get _mark =>
+      new ParserState(_peekToken, _previousToken, tokenizer);
+
+  /** Restores the parser/tokenizer state to state remembered by _mark. */
+  void _restore(ParserState markedData) {
+    tokenizer.restore(markedData);
+    _peekToken = markedData.peekToken;
+    _previousToken = markedData.previousToken;
+  }
+
+  bool _maybeEat(int kind, {unicodeRange : false}) {
+    if (_peekToken.kind == kind) {
+      _previousToken = _peekToken;
+      _peekToken = tokenizer.next(unicodeRange: unicodeRange);
+      return true;
+    } else {
+      return false;
+    }
+  }
+
+  void _eat(int kind, {unicodeRange : false}) {
+    if (!_maybeEat(kind, unicodeRange: unicodeRange)) {
+      _errorExpected(TokenKind.kindToString(kind));
+    }
+  }
+
+  void _eatSemicolon() {
+    _eat(TokenKind.SEMICOLON);
+  }
+
+  void _errorExpected(String expected) {
+    var tok = _next();
+    var message;
+    try {
+      message = 'expected $expected, but found $tok';
+    } catch (e) {
+      message = 'parsing error expected $expected';
+    }
+    _error(message, tok.span);
+  }
+
+  void _error(String message, Span location) {
+    if (location == null) {
+      location = _peekToken.span;
+    }
+    messages.error(message, location);
+  }
+
+  void _warning(String message, Span location) {
+    if (location == null) {
+      location = _peekToken.span;
+    }
+    messages.warning(message, location);
+  }
+
+  Span _makeSpan(int start) {
+    // TODO(terry): there are places where we are creating spans before we eat
+    // the tokens, so using _previousToken.end is not always valid.
+    var end = _previousToken != null && _previousToken.end >= start
+        ? _previousToken.end : _peekToken.end;
+    return file.span(start, end);
+  }
+
+  ///////////////////////////////////////////////////////////////////
+  // Top level productions
+  ///////////////////////////////////////////////////////////////////
+
+  /**
+   * The media_query_list production below replaces the media_list production
+   * from CSS2 the new grammar is:
+   *
+   *   media_query_list
+   *    : S* [media_query [ ',' S* media_query ]* ]?
+   *   media_query
+   *    : [ONLY | NOT]? S* media_type S* [ AND S* expression ]*
+   *    | expression [ AND S* expression ]*
+   *   media_type
+   *    : IDENT
+   *   expression
+   *    : '(' S* media_feature S* [ ':' S* expr ]? ')' S*
+   *   media_feature
+   *    : IDENT
+   */
+  List<MediaQuery> processMediaQueryList() {
+    var mediaQueries = [];
+
+    bool firstTime = true;
+    var mediaQuery;
+    do {
+      mediaQuery = processMediaQuery(firstTime == true);
+      if (mediaQuery != null) {
+        mediaQueries.add(mediaQuery);
+        firstTime = false;
+        continue;
+      }
+
+      // Any more more media types separated by comma.
+      if (!_maybeEat(TokenKind.COMMA)) break;
+
+      // Yep more media types start again.
+      firstTime = true;
+    } while ((!firstTime && mediaQuery != null) || firstTime);
+
+    return mediaQueries;
+  }
+
+  MediaQuery processMediaQuery([bool startQuery = true]) {
+    // Grammar: [ONLY | NOT]? S* media_type S*
+    //          [ AND S* MediaExpr ]* | MediaExpr [ AND S* MediaExpr ]*
+
+    int start = _peekToken.start;
+
+    // Is it a unary media operator?
+    var op = _peekToken.text;
+    var opLen = op.length;
+    var unaryOp = TokenKind.matchMediaOperator(op, 0, opLen);
+    if (unaryOp != -1) {
+      if (isChecked) {
+        if (startQuery &&
+            unaryOp != TokenKind.MEDIA_OP_NOT ||
+            unaryOp != TokenKind.MEDIA_OP_ONLY) {
+          _warning("Only the unary operators NOT and ONLY allowed",
+              _makeSpan(start));
+        }
+        if (!startQuery && unaryOp != TokenKind.MEDIA_OP_AND) {
+          _warning("Only the binary AND operator allowed", _makeSpan(start));
+        }
+      }
+      _next();
+      start = _peekToken.start;
+    }
+
+    var type;
+    if (startQuery && unaryOp != TokenKind.MEDIA_OP_AND) {
+      // Get the media type.
+      if (_peekIdentifier()) type = identifier();
+    }
+
+    var exprs = [];
+
+    if (unaryOp == -1 || unaryOp == TokenKind.MEDIA_OP_AND) {
+      var andOp = false;
+      while (true) {
+        var expr = processMediaExpression(andOp);
+        if (expr == null) break;
+
+        exprs.add(expr);
+        op = _peekToken.text;
+        opLen = op.length;
+        andOp = TokenKind.matchMediaOperator(op, 0, opLen) ==
+            TokenKind.MEDIA_OP_AND;
+        if (!andOp) break;
+        _next();
+      }
+    }
+
+    if (unaryOp != -1 || type != null || exprs.length > 0) {
+      return new MediaQuery(unaryOp, type, exprs, _makeSpan(start));
+    }
+  }
+
+  MediaExpression processMediaExpression([bool andOperator = false]) {
+    int start = _peekToken.start;
+
+    // Grammar: '(' S* media_feature S* [ ':' S* expr ]? ')' S*
+    if (_maybeEat(TokenKind.LPAREN)) {
+      if (_peekIdentifier()) {
+        var feature = identifier();           // Media feature.
+        while (_maybeEat(TokenKind.COLON)) {
+          int startExpr = _peekToken.start;
+          var exprs = processExpr();
+          if (_maybeEat(TokenKind.RPAREN)) {
+            return new MediaExpression(andOperator, feature, exprs,
+                _makeSpan(startExpr));
+          } else if (isChecked) {
+            _warning("Missing parenthesis around media expression",
+                _makeSpan(start));
+            return null;
+          }
+        }
+      } else if (isChecked) {
+        _warning("Missing media feature in media expression", _makeSpan(start));
+        return null;
+      }
+    }
+  }
+
+  //  Directive grammar:
+  //
+  //  import:             '@import' [string | URI] media_list?
+  //  media:              '@media' media_query_list '{' ruleset '}'
+  //  page:               '@page' [':' IDENT]? '{' declarations '}'
+  //  stylet:             '@stylet' IDENT '{' ruleset '}'
+  //  media_query_list:   IDENT [',' IDENT]
+  //  keyframes:          '@-webkit-keyframes ...' (see grammar below).
+  //  font_face:          '@font-face' '{' declarations '}'
+  //  namespace:          '@namespace name url("xmlns")
+  //  host:               '@host '{' ruleset '}'
+  processDirective() {
+    int start = _peekToken.start;
+
+    var tokId = _peek();
+    // Handle case for @ directive (where there's a whitespace between the @
+    // sign and the directive name.  Technically, it's not valid grammar but
+    // a number of CSS tests test for whitespace between @ and name.
+    if (tokId == TokenKind.AT) {
+      Token tok = _next();
+      tokId = _peek();
+      if (_peekIdentifier()) {
+        // Is it a directive?
+        var directive = _peekToken.text;
+        var directiveLen = directive.length;
+        tokId = TokenKind.matchDirectives(directive, 0, directiveLen);
+        if (tokId == -1) {
+          tokId = TokenKind.matchMarginDirectives(directive, 0, directiveLen);
+        }
+      }
+
+      if (tokId == -1) {
+        if (messages.options.lessSupport) {
+          // Less compatibility:
+          //    @name: value;      =>    var-name: value;       (VarDefinition)
+          //    property: @name;   =>    property: var(name);   (VarUsage)
+          var name;
+          if (_peekIdentifier()) {
+            name = identifier();
+          }
+
+          _eat(TokenKind.COLON);
+
+          Expressions exprs = processExpr();
+
+          var span = _makeSpan(start);
+          return new VarDefinitionDirective(
+              new VarDefinition(name, exprs, span), span);
+        } else if (isChecked) {
+          _error('unexpected directive @$_peekToken', _peekToken.span);
+        }
+      }
+    }
+
+    switch (tokId) {
+      case TokenKind.DIRECTIVE_IMPORT:
+        _next();
+
+        // @import "uri_string" or @import url("uri_string") are identical; only
+        // a url can follow an @import.
+        String importStr;
+        if (_peekIdentifier()) {
+          var func = processFunction(identifier());
+          if (func is UriTerm) {
+            importStr = func.text;
+          }
+        } else {
+          importStr = processQuotedString(false);
+        }
+
+        // Any medias?
+        var medias = processMediaQueryList();
+
+        if (importStr == null) {
+          _error('missing import string', _peekToken.span);
+        }
+
+        return new ImportDirective(importStr.trim(), medias, _makeSpan(start));
+
+      case TokenKind.DIRECTIVE_MEDIA:
+        _next();
+
+        // Any medias?
+        var media = processMediaQueryList();
+
+        List<TreeNode> rulesets = [];
+        if (_maybeEat(TokenKind.LBRACE)) {
+          while (!_maybeEat(TokenKind.END_OF_FILE)) {
+            RuleSet ruleset = processRuleSet();
+            if (ruleset == null) break;
+            rulesets.add(ruleset);
+          }
+
+          if (!_maybeEat(TokenKind.RBRACE)) {
+            _error('expected } after ruleset for @media', _peekToken.span);
+          }
+        } else {
+          _error('expected { after media before ruleset', _peekToken.span);
+        }
+        return new MediaDirective(media, rulesets, _makeSpan(start));
+
+      case TokenKind.DIRECTIVE_HOST:
+        _next();
+
+        List<TreeNode> rulesets = [];
+        if (_maybeEat(TokenKind.LBRACE)) {
+          while (!_maybeEat(TokenKind.END_OF_FILE)) {
+            RuleSet ruleset = processRuleSet();
+            if (ruleset == null) break;
+            rulesets.add(ruleset);
+          }
+
+          if (!_maybeEat(TokenKind.RBRACE)) {
+            _error('expected } after ruleset for @host', _peekToken.span);
+          }
+        } else {
+          _error('expected { after host before ruleset', _peekToken.span);
+        }
+        return new HostDirective(rulesets, _makeSpan(start));
+
+      case TokenKind.DIRECTIVE_PAGE:
+        /*
+         * @page S* IDENT? pseudo_page?
+         *      S* '{' S*
+         *      [ declaration | margin ]?
+         *      [ ';' S* [ declaration | margin ]? ]* '}' S*
+         *
+         * pseudo_page :
+         *      ':' [ "left" | "right" | "first" ]
+         *
+         * margin :
+         *      margin_sym S* '{' declaration [ ';' S* declaration? ]* '}' S*
+         *
+         * margin_sym : @top-left-corner, @top-left, @bottom-left, etc.
+         *
+         * See http://www.w3.org/TR/css3-page/#CSS21
+         */
+        _next();
+
+        // Page name
+        var name;
+        if (_peekIdentifier()) {
+          name = identifier();
+        }
+
+        // Any pseudo page?
+        var pseudoPage;
+        if (_maybeEat(TokenKind.COLON)) {
+          if (_peekIdentifier()) {
+            pseudoPage = identifier();
+            // TODO(terry): Normalize pseudoPage to lowercase.
+            if (isChecked &&
+                !(pseudoPage.name == 'left' ||
+                  pseudoPage.name == 'right' ||
+                  pseudoPage.name == 'first')) {
+              _warning("Pseudo page must be left, top or first",
+                  pseudoPage.span);
+              return;
+            }
+          }
+        }
+
+        String pseudoName = pseudoPage is Identifier ? pseudoPage.name : '';
+        String ident = name is Identifier ? name.name : '';
+        return new PageDirective(ident, pseudoName,
+            processMarginsDeclarations(), _makeSpan(start));
+
+      case TokenKind.DIRECTIVE_CHARSET:
+        // @charset S* STRING S* ';'
+        _next();
+
+        var charEncoding = processQuotedString(false);
+        if (isChecked && charEncoding == null) {
+          // Missing character encoding.
+          _warning('missing character encoding string', _makeSpan(start));
+        }
+
+        return new CharsetDirective(charEncoding, _makeSpan(start));
+
+      // TODO(terry): Workaround Dart2js bug continue not implemented in switch
+      //              see https://code.google.com/p/dart/issues/detail?id=8270
+      /*
+      case TokenKind.DIRECTIVE_MS_KEYFRAMES:
+        // TODO(terry): For now only IE 10 (are base level) supports @keyframes,
+        // -moz- has only been optional since Oct 2012 release of Firefox, not
+        // all versions of webkit support @keyframes and opera doesn't yet
+        // support w/o -o- prefix.  Add more warnings for other prefixes when
+        // they become optional.
+        if (isChecked) {
+          _warning('@-ms-keyframes should be @keyframes', _makeSpan(start));
+        }
+        continue keyframeDirective;
+
+      keyframeDirective:
+      */
+      case TokenKind.DIRECTIVE_KEYFRAMES:
+      case TokenKind.DIRECTIVE_WEB_KIT_KEYFRAMES:
+      case TokenKind.DIRECTIVE_MOZ_KEYFRAMES:
+      case TokenKind.DIRECTIVE_O_KEYFRAMES:
+      // TODO(terry): Remove workaround when bug 8270 is fixed.
+      case TokenKind.DIRECTIVE_MS_KEYFRAMES:
+        if (tokId == TokenKind.DIRECTIVE_MS_KEYFRAMES && isChecked) {
+          _warning('@-ms-keyframes should be @keyframes', _makeSpan(start));
+        }
+      // TODO(terry): End of workaround.
+
+        /*  Key frames grammar:
+         *
+         *  @[browser]? keyframes [IDENT|STRING] '{' keyframes-blocks '}';
+         *
+         *  browser: [-webkit-, -moz-, -ms-, -o-]
+         *
+         *  keyframes-blocks:
+         *    [keyframe-selectors '{' declarations '}']* ;
+         *
+         *  keyframe-selectors:
+         *    ['from'|'to'|PERCENTAGE] [',' ['from'|'to'|PERCENTAGE] ]* ;
+         */
+        _next();
+
+        var name;
+        if (_peekIdentifier()) {
+          name = identifier();
+        }
+
+        _eat(TokenKind.LBRACE);
+
+        var keyframe = new KeyFrameDirective(tokId, name, _makeSpan(start));
+
+        do {
+          Expressions selectors = new Expressions(_makeSpan(start));
+
+          do {
+            var term = processTerm();
+
+            // TODO(terry): Only allow from, to and PERCENTAGE ...
+
+            selectors.add(term);
+          } while (_maybeEat(TokenKind.COMMA));
+
+          keyframe.add(new KeyFrameBlock(selectors, processDeclarations(),
+              _makeSpan(start)));
+
+        } while (!_maybeEat(TokenKind.RBRACE) && !isPrematureEndOfFile());
+
+        return keyframe;
+
+      case TokenKind.DIRECTIVE_FONTFACE:
+        _next();
+        return new FontFaceDirective(processDeclarations(), _makeSpan(start));
+
+      case TokenKind.DIRECTIVE_STYLET:
+        /* Stylet grammar:
+         *
+         *  @stylet IDENT '{'
+         *    ruleset
+         *  '}'
+         */
+        _next();
+
+        var name;
+        if (_peekIdentifier()) {
+          name = identifier();
+        }
+
+        _eat(TokenKind.LBRACE);
+
+        List<TreeNode> productions = [];
+
+        start = _peekToken.start;
+        while (!_maybeEat(TokenKind.END_OF_FILE)) {
+          RuleSet ruleset = processRuleSet();
+          if (ruleset == null) {
+            break;
+          }
+          productions.add(ruleset);
+        }
+
+        _eat(TokenKind.RBRACE);
+
+        return new StyletDirective(name, productions, _makeSpan(start));
+
+      case TokenKind.DIRECTIVE_NAMESPACE:
+        /* Namespace grammar:
+         *
+         * @namespace S* [namespace_prefix S*]? [STRING|URI] S* ';' S*
+         * namespace_prefix : IDENT
+         *
+         */
+        _next();
+
+        var prefix;
+        if (_peekIdentifier()) {
+          prefix = identifier();
+        }
+
+        // The namespace URI can be either a quoted string url("uri_string")
+        // are identical.
+        String namespaceUri;
+        if (_peekIdentifier()) {
+          var func = processFunction(identifier());
+          if (func is UriTerm) {
+            namespaceUri = func.text;
+          }
+        } else {
+          if (prefix != null && prefix.name == 'url') {
+            var func = processFunction(prefix);
+            if (func is UriTerm) {
+              // @namespace url("");
+              namespaceUri = func.text;
+              prefix = null;
+            }
+          } else {
+            namespaceUri = processQuotedString(false);
+          }
+        }
+
+        return new NamespaceDirective(prefix != null ? prefix.name : '',
+            namespaceUri, _makeSpan(start));
+    }
+  }
+
+  RuleSet processRuleSet([SelectorGroup selectorGroup]) {
+    if (selectorGroup == null) {
+      selectorGroup = processSelectorGroup();
+    }
+    if (selectorGroup != null) {
+      return new RuleSet(selectorGroup, processDeclarations(),
+          selectorGroup.span);
+    }
+  }
+
+  /**
+   * Look ahead to see if what should be a declaration is really a selector.
+   * If it's a selector than it's a nested selector.  This support's Less'
+   * nested selector syntax (requires a look ahead). E.g.,
+   *
+   *    div {
+   *      width : 20px;
+   *      span {
+   *        color: red;
+   *      }
+   *    }
+   *
+   * Two tag name selectors div and span equivalent to:
+   *
+   *    div {
+   *      width: 20px;
+   *    }
+   *    div span {
+   *      color: red;
+   *    }
+   *
+   * Return [null] if no selector or [SelectorGroup] if a selector was parsed.
+   */
+  SelectorGroup _nestedSelector() {
+    Messages oldMessages = messages;
+    _createMessages();
+
+    var markedData = _mark;
+
+    // Look a head do we have a nested selector instead of a declaration?
+    SelectorGroup selGroup = processSelectorGroup();
+
+    var nestedSelector = selGroup != null && _peekKind(TokenKind.LBRACE) &&
+        messages.messages.isEmpty;
+
+    if (!nestedSelector) {
+      // Not a selector so restore the world.
+      _restore(markedData);
+      messages = oldMessages;
+      return null;
+    } else {
+      // Remember any messages from look ahead.
+      oldMessages.mergeMessages(messages);
+      messages = oldMessages;
+      return selGroup;
+    }
+  }
+
+  processDeclarations({bool checkBrace: true}) {
+    int start = _peekToken.start;
+
+    if (checkBrace) _eat(TokenKind.LBRACE);
+
+    List decls = [];
+    List dartStyles = [];             // List of latest styles exposed to Dart.
+
+    do {
+      var selectorGroup = _nestedSelector();
+      while (selectorGroup != null) {
+        // Nested selector so process as a ruleset.
+        var ruleset = processRuleSet(selectorGroup);
+        decls.add(ruleset);
+        selectorGroup = _nestedSelector();
+      }
+
+      Declaration decl = processDeclaration(dartStyles);
+      if (decl != null) {
+        if (decl.hasDartStyle) {
+          var newDartStyle = decl.dartStyle;
+
+          // Replace or add latest Dart style.
+          bool replaced = false;
+          for (var i = 0; i < dartStyles.length; i++) {
+            var dartStyle = dartStyles[i];
+            if (dartStyle.isSame(newDartStyle)) {
+              dartStyles[i] = newDartStyle;
+              replaced = true;
+              break;
+            }
+          }
+          if (!replaced) {
+            dartStyles.add(newDartStyle);
+          }
+        }
+        decls.add(decl);
+      }
+    } while (_maybeEat(TokenKind.SEMICOLON));
+
+    if (checkBrace) _eat(TokenKind.RBRACE);
+
+    // Fixup declaration to only have dartStyle that are live for this set of
+    // declarations.
+    for (var decl in decls) {
+      if (decl is Declaration) {
+        if (decl.hasDartStyle && dartStyles.indexOf(decl.dartStyle) < 0) {
+          // Dart style not live, ignore these styles in this Declarations.
+          decl.dartStyle = null;
+        }
+      }
+    }
+
+    return new DeclarationGroup(decls, _makeSpan(start));
+  }
+
+  List<DeclarationGroup> processMarginsDeclarations() {
+    List groups = [];
+
+    int start = _peekToken.start;
+
+    _eat(TokenKind.LBRACE);
+
+    List<Declaration> decls = [];
+    List dartStyles = [];             // List of latest styles exposed to Dart.
+
+    do {
+      switch (_peek()) {
+        case TokenKind.MARGIN_DIRECTIVE_TOPLEFTCORNER:
+        case TokenKind.MARGIN_DIRECTIVE_TOPLEFT:
+        case TokenKind.MARGIN_DIRECTIVE_TOPCENTER:
+        case TokenKind.MARGIN_DIRECTIVE_TOPRIGHT:
+        case TokenKind.MARGIN_DIRECTIVE_TOPRIGHTCORNER:
+        case TokenKind.MARGIN_DIRECTIVE_BOTTOMLEFTCORNER:
+        case TokenKind.MARGIN_DIRECTIVE_BOTTOMLEFT:
+        case TokenKind.MARGIN_DIRECTIVE_BOTTOMCENTER:
+        case TokenKind.MARGIN_DIRECTIVE_BOTTOMRIGHT:
+        case TokenKind.MARGIN_DIRECTIVE_BOTTOMRIGHTCORNER:
+        case TokenKind.MARGIN_DIRECTIVE_LEFTTOP:
+        case TokenKind.MARGIN_DIRECTIVE_LEFTMIDDLE:
+        case TokenKind.MARGIN_DIRECTIVE_LEFTBOTTOM:
+        case TokenKind.MARGIN_DIRECTIVE_RIGHTTOP:
+        case TokenKind.MARGIN_DIRECTIVE_RIGHTMIDDLE:
+        case TokenKind.MARGIN_DIRECTIVE_RIGHTBOTTOM:
+          // Margin syms processed.
+          //   margin :
+          //      margin_sym S* '{' declaration [ ';' S* declaration? ]* '}' S*
+          //
+          //      margin_sym : @top-left-corner, @top-left, @bottom-left, etc.
+          var marginSym = _peek();
+
+          _next();
+
+          var declGroup = processDeclarations();
+          if (declGroup != null) {
+            groups.add(new MarginGroup(marginSym, declGroup.declarations,
+                _makeSpan(start)));
+          }
+          break;
+        default:
+          Declaration decl = processDeclaration(dartStyles);
+          if (decl != null) {
+            if (decl.hasDartStyle) {
+              var newDartStyle = decl.dartStyle;
+
+              // Replace or add latest Dart style.
+              bool replaced = false;
+              for (var i = 0; i < dartStyles.length; i++) {
+                var dartStyle = dartStyles[i];
+                if (dartStyle.isSame(newDartStyle)) {
+                  dartStyles[i] = newDartStyle;
+                  replaced = true;
+                  break;
+                }
+              }
+              if (!replaced) {
+                dartStyles.add(newDartStyle);
+              }
+            }
+            decls.add(decl);
+          }
+          _maybeEat(TokenKind.SEMICOLON);
+          break;
+      }
+    } while (!_maybeEat(TokenKind.RBRACE) && !isPrematureEndOfFile());
+
+    // Fixup declaration to only have dartStyle that are live for this set of
+    // declarations.
+    for (var decl in decls) {
+      if (decl.hasDartStyle && dartStyles.indexOf(decl.dartStyle) < 0) {
+        // Dart style not live, ignore these styles in this Declarations.
+        decl.dartStyle = null;
+      }
+    }
+
+    if (decls.length > 0) {
+      groups.add(new DeclarationGroup(decls, _makeSpan(start)));
+    }
+
+    return groups;
+  }
+
+  SelectorGroup processSelectorGroup() {
+    List<Selector> selectors = [];
+    int start = _peekToken.start;
+    do {
+      Selector selector = processSelector();
+      if (selector != null) {
+        selectors.add(selector);
+      }
+    } while (_maybeEat(TokenKind.COMMA));
+
+    if (selectors.length > 0) {
+      return new SelectorGroup(selectors, _makeSpan(start));
+    }
+  }
+
+  /**
+   * Return list of selectors
+   */
+  processSelector() {
+    List<SimpleSelectorSequence> simpleSequences = [];
+    int start = _peekToken.start;
+    while (true) {
+      // First item is never descendant make sure it's COMBINATOR_NONE.
+      var selectorItem = simpleSelectorSequence(simpleSequences.length == 0);
+      if (selectorItem != null) {
+        simpleSequences.add(selectorItem);
+      } else {
+        break;
+      }
+    }
+
+    if (simpleSequences.length > 0) {
+      return new Selector(simpleSequences, _makeSpan(start));
+    }
+  }
+
+  simpleSelectorSequence(bool forceCombinatorNone) {
+    var start = _peekToken.start;
+    var combinatorType = TokenKind.COMBINATOR_NONE;
+    var thisOperator = false;
+
+    switch (_peek()) {
+      case TokenKind.PLUS:
+        _eat(TokenKind.PLUS);
+        combinatorType = TokenKind.COMBINATOR_PLUS;
+        break;
+      case TokenKind.GREATER:
+        _eat(TokenKind.GREATER);
+        combinatorType = TokenKind.COMBINATOR_GREATER;
+        break;
+      case TokenKind.TILDE:
+        _eat(TokenKind.TILDE);
+        combinatorType = TokenKind.COMBINATOR_TILDE;
+        break;
+      case TokenKind.AMPERSAND:
+        _eat(TokenKind.AMPERSAND);
+        thisOperator = true;
+        break;
+      }
+
+    // Check if WHITESPACE existed between tokens if so we're descendent.
+    if (combinatorType == TokenKind.COMBINATOR_NONE && !forceCombinatorNone) {
+      if (this._previousToken != null &&
+          this._previousToken.end != this._peekToken.start) {
+        combinatorType = TokenKind.COMBINATOR_DESCENDANT;
+      }
+    }
+
+    var span = _makeSpan(start);
+    var simpleSel = thisOperator ?
+        new ElementSelector(new ThisOperator(span), span) : simpleSelector();
+    if (simpleSel == null &&
+        (combinatorType == TokenKind.COMBINATOR_PLUS ||
+        combinatorType == TokenKind.COMBINATOR_GREATER ||
+        combinatorType == TokenKind.COMBINATOR_TILDE)) {
+      // For "+ &", "~ &" or "> &" a selector sequence with no name is needed
+      // so that the & will have a combinator too.  This is needed to
+      // disambiguate selector expressions:
+      //    .foo&:hover     combinator before & is NONE
+      //    .foo &          combinator before & is DESCDENDANT
+      //    .foo > &        combinator before & is GREATER
+      simpleSel =  new ElementSelector(new Identifier("", span), span);
+    }
+    if (simpleSel != null) {
+      return new SimpleSelectorSequence(simpleSel, span, combinatorType);
+    }
+  }
+
+  /**
+   * Simple selector grammar:
+   *
+   *    simple_selector_sequence
+   *       : [ type_selector | universal ]
+   *         [ HASH | class | attrib | pseudo | negation ]*
+   *       | [ HASH | class | attrib | pseudo | negation ]+
+   *    type_selector
+   *       : [ namespace_prefix ]? element_name
+   *    namespace_prefix
+   *       : [ IDENT | '*' ]? '|'
+   *    element_name
+   *       : IDENT
+   *    universal
+   *       : [ namespace_prefix ]? '*'
+   *    class
+   *       : '.' IDENT
+   */
+  simpleSelector() {
+    // TODO(terry): Nathan makes a good point parsing of namespace and element
+    //              are essentially the same (asterisk or identifier) other
+    //              than the error message for element.  Should consolidate the
+    //              code.
+    // TODO(terry): Need to handle attribute namespace too.
+    var first;
+    int start = _peekToken.start;
+    switch (_peek()) {
+      case TokenKind.ASTERISK:
+        // Mark as universal namespace.
+        var tok = _next();
+        first = new Wildcard(_makeSpan(tok.start));
+        break;
+      case TokenKind.IDENTIFIER:
+        first = identifier();
+        break;
+      default:
+        // Expecting simple selector.
+        // TODO(terry): Could be a synthesized token like value, etc.
+        if (TokenKind.isKindIdentifier(_peek())) {
+          first = identifier();
+        } else if (_peekKind(TokenKind.SEMICOLON)) {
+          // Can't be a selector if we found a semi-colon.
+          return null;
+        }
+        break;
+    }
+
+    if (_maybeEat(TokenKind.NAMESPACE)) {
+      var element;
+      switch (_peek()) {
+        case TokenKind.ASTERISK:
+          // Mark as universal element
+          var tok = _next();
+          element = new Wildcard(_makeSpan(tok.start));
+          break;
+        case TokenKind.IDENTIFIER:
+          element = identifier();
+          break;
+        default:
+          _error('expected element name or universal(*), but found $_peekToken',
+              _peekToken.span);
+          break;
+      }
+
+      return new NamespaceSelector(first,
+          new ElementSelector(element, element.span), _makeSpan(start));
+    } else if (first != null) {
+      return new ElementSelector(first, _makeSpan(start));
+    } else {
+      // Check for HASH | class | attrib | pseudo | negation
+      return simpleSelectorTail();
+    }
+  }
+
+  bool _anyWhiteSpaceBeforePeekToken(int kind) {
+    if (_previousToken != null && _peekToken != null &&
+        _previousToken.kind == kind) {
+      // If end of previous token isn't same as the start of peek token then
+      // there's something between these tokens probably whitespace.
+      return _previousToken.end != _peekToken.start;
+    }
+
+    return false;
+  }
+
+  /**
+   * type_selector | universal | HASH | class | attrib | pseudo
+   */
+  simpleSelectorTail() {
+    // Check for HASH | class | attrib | pseudo | negation
+    int start = _peekToken.start;
+    switch (_peek()) {
+      case TokenKind.HASH:
+        _eat(TokenKind.HASH);
+
+        bool hasWhiteSpace = false;
+        if (_anyWhiteSpaceBeforePeekToken(TokenKind.HASH)) {
+          _warning("Not a valid ID selector expected #id", _makeSpan(start));
+          hasWhiteSpace = true;
+        }
+        if (_peekIdentifier()) {
+          var id = identifier();
+          if (hasWhiteSpace) {
+            // Generate bad selector id (normalized).
+            id.name = " ${id.name}";
+          }
+          return new IdSelector(id, _makeSpan(start));
+        }
+        return null;
+      case TokenKind.DOT:
+        _eat(TokenKind.DOT);
+
+        bool hasWhiteSpace = false;
+        if (_anyWhiteSpaceBeforePeekToken(TokenKind.DOT)) {
+          _warning("Not a valid class selector expected .className",
+              _makeSpan(start));
+          hasWhiteSpace = true;
+        }
+        var id = identifier();
+        if (hasWhiteSpace) {
+          // Generate bad selector class (normalized).
+          id.name = " ${id.name}";
+        }
+        return new ClassSelector(id, _makeSpan(start));
+      case TokenKind.COLON:
+        // :pseudo-class ::pseudo-element
+        // TODO(terry): '::' should be token.
+        _eat(TokenKind.COLON);
+        bool pseudoElement = _maybeEat(TokenKind.COLON);
+
+        // TODO(terry): If no identifier specified consider optimizing out the
+        //              : or :: and making this a normal selector.  For now,
+        //              create an empty pseudoName.
+        var pseudoName;
+        if (_peekIdentifier()) {
+          pseudoName = identifier();
+        } else {
+          return null;
+        }
+
+        // Functional pseudo?
+        if (_maybeEat(TokenKind.LPAREN)) {
+          if (!pseudoElement && pseudoName.name.toLowerCase() == 'not') {
+            // Negation :   ':NOT(' S* negation_arg S* ')'
+            var negArg = simpleSelector();
+
+            _eat(TokenKind.RPAREN);
+            return new NegationSelector(negArg, _makeSpan(start));
+          } else {
+            // Handle function expression.
+            var span = _makeSpan(start);
+            var expr = processSelectorExpression();
+
+            // Used during selector look-a-head if not a SelectorExpression is
+            // bad.
+            if (expr is! SelectorExpression) {
+              _errorExpected("CSS expression");
+              return null;
+            }
+
+            _eat(TokenKind.RPAREN);
+            return (pseudoElement) ?
+                new PseudoElementFunctionSelector(pseudoName, expr, span) :
+                new PseudoClassFunctionSelector(pseudoName, expr, span);
+          }
+        }
+
+        // TODO(terry): Need to handle specific pseudo class/element name and
+        // backward compatible names that are : as well as :: as well as
+        // parameters.  Current, spec uses :: for pseudo-element and : for
+        // pseudo-class.  However, CSS2.1 allows for : to specify old
+        // pseudo-elements (:first-line, :first-letter, :before and :after) any
+        // new pseudo-elements defined would require a ::.
+        return pseudoElement ?
+            new PseudoElementSelector(pseudoName, _makeSpan(start)) :
+            new PseudoClassSelector(pseudoName, _makeSpan(start));
+      case TokenKind.LBRACK:
+        return processAttribute();
+      case TokenKind.DOUBLE:
+        _error('name must start with a alpha character, but found a number',
+            _peekToken.span);
+        _next();
+        break;
+    }
+  }
+
+  /**
+   *  In CSS3, the expressions are identifiers, strings, or of the form "an+b".
+   *
+   *    : [ [ PLUS | '-' | DIMENSION | NUMBER | STRING | IDENT ] S* ]+
+   *
+   *    num               [0-9]+|[0-9]*\.[0-9]+
+   *    PLUS              '+'
+   *    DIMENSION         {num}{ident}
+   *    NUMBER            {num}
+   */
+  processSelectorExpression() {
+    int start = _peekToken.start;
+
+    var expression = new SelectorExpression(_makeSpan(start));
+
+    Token termToken;
+    var value;
+
+    // Special parsing for expressions in pseudo functions.  Minus is used as
+    // operator not identifier.
+    tokenizer.selectorExpression = true;
+
+    bool keepParsing = true;
+    while (keepParsing) {
+      switch (_peek()) {
+        case TokenKind.PLUS:
+          start = _peekToken.start;
+          termToken = _next();
+          expression.add(new OperatorPlus(_makeSpan(start)));
+          break;
+        case TokenKind.MINUS:
+          start = _peekToken.start;
+          termToken = _next();
+          expression.add(new OperatorMinus(_makeSpan(start)));
+          break;
+        case TokenKind.INTEGER:
+          termToken = _next();
+          value = int.parse(termToken.text);
+          break;
+        case TokenKind.DOUBLE:
+          termToken = _next();
+          value = double.parse(termToken.text);
+          break;
+        case TokenKind.SINGLE_QUOTE:
+        case TokenKind.DOUBLE_QUOTE:
+          value = processQuotedString(false);
+          value = '"${_escapeString(value)}"';
+          return new LiteralTerm(value, value, _makeSpan(start));
+        case TokenKind.IDENTIFIER:
+          value = identifier();   // Snarf up the ident we'll remap, maybe.
+          break;
+        default:
+          keepParsing = false;
+      }
+
+      if (keepParsing && value != null) {
+        var unitTerm;
+        // Don't process the dimension if MINUS or PLUS is next.
+        if (_peek() != TokenKind.MINUS && _peek() != TokenKind.PLUS) {
+          unitTerm = processDimension(termToken, value, _makeSpan(start));
+        }
+        if (unitTerm == null) {
+          unitTerm = new LiteralTerm(value, value.name, _makeSpan(start));
+        }
+        expression.add(unitTerm);
+
+        value = null;
+      }
+    }
+
+    tokenizer.selectorExpression = false;
+
+    return expression;
+  }
+
+  //  Attribute grammar:
+  //
+  //  attributes :
+  //    '[' S* IDENT S* [ ATTRIB_MATCHES S* [ IDENT | STRING ] S* ]? ']'
+  //
+  //  ATTRIB_MATCHES :
+  //    [ '=' | INCLUDES | DASHMATCH | PREFIXMATCH | SUFFIXMATCH | SUBSTRMATCH ]
+  //
+  //  INCLUDES:         '~='
+  //
+  //  DASHMATCH:        '|='
+  //
+  //  PREFIXMATCH:      '^='
+  //
+  //  SUFFIXMATCH:      '$='
+  //
+  //  SUBSTRMATCH:      '*='
+  //
+  //
+  processAttribute() {
+    int start = _peekToken.start;
+
+    if (_maybeEat(TokenKind.LBRACK)) {
+      var attrName = identifier();
+
+      int op;
+      switch (_peek()) {
+      case TokenKind.EQUALS:
+      case TokenKind.INCLUDES:        // ~=
+      case TokenKind.DASH_MATCH:      // |=
+      case TokenKind.PREFIX_MATCH:    // ^=
+      case TokenKind.SUFFIX_MATCH:    // $=
+      case TokenKind.SUBSTRING_MATCH: // *=
+        op = _peek();
+        _next();
+        break;
+      default:
+        op = TokenKind.NO_MATCH;
+      }
+
+      var value;
+      if (op != TokenKind.NO_MATCH) {
+        // Operator hit so we require a value too.
+        if (_peekIdentifier()) {
+          value = identifier();
+        } else {
+          value = processQuotedString(false);
+        }
+
+        if (value == null) {
+          _error('expected attribute value string or ident', _peekToken.span);
+        }
+      }
+
+      _eat(TokenKind.RBRACK);
+
+      return new AttributeSelector(attrName, op, value, _makeSpan(start));
+    }
+  }
+
+  //  Declaration grammar:
+  //
+  //  declaration:  property ':' expr prio?
+  //
+  //  property:  IDENT [or IE hacks]
+  //  prio:      !important
+  //  expr:      (see processExpr)
+  //
+  // Here are the ugly IE hacks we need to support:
+  //   property: expr prio? \9; - IE8 and below property, /9 before semi-colon
+  //   *IDENT                   - IE7 or below
+  //   _IDENT                   - IE6 property (automatically a valid ident)
+  //
+  processDeclaration(List dartStyles) {
+    Declaration decl;
+
+    int start = _peekToken.start;
+
+    // IE7 hack of * before property name if so the property is IE7 or below.
+    var ie7 = _peekKind(TokenKind.ASTERISK);
+    if (ie7) {
+      _next();
+    }
+
+    // IDENT ':' expr '!important'?
+    if (TokenKind.isIdentifier(_peekToken.kind)) {
+      var propertyIdent = identifier();
+
+      var ieFilterProperty = propertyIdent.name.toLowerCase() == 'filter';
+
+      _eat(TokenKind.COLON);
+
+      Expressions exprs = processExpr(ieFilterProperty);
+
+      var dartComposite = _styleForDart(propertyIdent, exprs, dartStyles);
+
+      // Handle !important (prio)
+      var importantPriority = _maybeEat(TokenKind.IMPORTANT);
+
+      decl = new Declaration(propertyIdent, exprs, dartComposite,
+          _makeSpan(start), important: importantPriority, ie7: ie7);
+    } else if (_peekToken.kind == TokenKind.VAR_DEFINITION) {
+      _next();
+      var definedName;
+      if (_peekIdentifier()) definedName = identifier();
+
+      _eat(TokenKind.COLON);
+
+      Expressions exprs = processExpr();
+
+      decl = new VarDefinition(definedName, exprs, _makeSpan(start));
+    }
+
+    return decl;
+  }
+
+  /** List of styles exposed to the Dart UI framework. */
+  static const int _fontPartFont= 0;
+  static const int _fontPartVariant = 1;
+  static const int _fontPartWeight = 2;
+  static const int _fontPartSize = 3;
+  static const int _fontPartFamily = 4;
+  static const int _fontPartStyle = 5;
+  static const int _marginPartMargin = 6;
+  static const int _marginPartLeft = 7;
+  static const int _marginPartTop = 8;
+  static const int _marginPartRight = 9;
+  static const int _marginPartBottom = 10;
+  static const int _lineHeightPart = 11;
+  static const int _borderPartBorder = 12;
+  static const int _borderPartLeft = 13;
+  static const int _borderPartTop = 14;
+  static const int _borderPartRight = 15;
+  static const int _borderPartBottom = 16;
+  static const int _borderPartWidth = 17;
+  static const int _borderPartLeftWidth = 18;
+  static const int _borderPartTopWidth = 19;
+  static const int _borderPartRightWidth = 20;
+  static const int _borderPartBottomWidth = 21;
+  static const int _heightPart = 22;
+  static const int _widthPart = 23;
+  static const int _paddingPartPadding = 24;
+  static const int _paddingPartLeft = 25;
+  static const int _paddingPartTop = 26;
+  static const int _paddingPartRight = 27;
+  static const int _paddingPartBottom = 28;
+
+  static const Map<String, int> _stylesToDart = const {
+    'font':                 _fontPartFont,
+    'font-family':          _fontPartFamily,
+    'font-size':            _fontPartSize,
+    'font-style':           _fontPartStyle,
+    'font-variant':         _fontPartVariant,
+    'font-weight':          _fontPartWeight,
+    'line-height':          _lineHeightPart,
+    'margin':               _marginPartMargin,
+    'margin-left':          _marginPartLeft,
+    'margin-right':         _marginPartRight,
+    'margin-top':           _marginPartTop,
+    'margin-bottom':        _marginPartBottom,
+    'border':               _borderPartBorder,
+    'border-left':          _borderPartLeft,
+    'border-right':         _borderPartRight,
+    'border-top':           _borderPartTop,
+    'border-bottom':        _borderPartBottom,
+    'border-width':         _borderPartWidth,
+    'border-left-width':    _borderPartLeftWidth,
+    'border-top-width':     _borderPartTopWidth,
+    'border-right-width':   _borderPartRightWidth,
+    'border-bottom-width':  _borderPartBottomWidth,
+    'height':               _heightPart,
+    'width':                _widthPart,
+    'padding':              _paddingPartPadding,
+    'padding-left':         _paddingPartLeft,
+    'padding-top':          _paddingPartTop,
+    'padding-right':        _paddingPartRight,
+    'padding-bottom':       _paddingPartBottom
+  };
+
+  static const Map<String, int> _nameToFontWeight = const {
+    'bold' : FontWeight.bold,
+    'normal' : FontWeight.normal
+  };
+
+  static _findStyle(String styleName) {
+    if (_stylesToDart.containsKey(styleName)) {
+      return _stylesToDart[styleName];
+    }
+  }
+
+  _styleForDart(Identifier property, Expressions exprs, List dartStyles) {
+    int styleType = _findStyle(property.name.toLowerCase());
+    if (styleType != null) {
+      return buildDartStyleNode(styleType, exprs, dartStyles);
+    }
+  }
+
+  FontExpression _mergeFontStyles(FontExpression fontExpr, List dartStyles) {
+    // Merge all font styles for this class selector.
+    for (var dartStyle in dartStyles) {
+      if (dartStyle.isFont) {
+        fontExpr = new FontExpression.merge(dartStyle, fontExpr);
+      }
+    }
+
+    return fontExpr;
+  }
+
+  buildDartStyleNode(int styleType, Expressions exprs, List dartStyles) {
+    switch (styleType) {
+      /*
+       * Properties in order:
+       *
+       *   font-style font-variant font-weight font-size/line-height font-family
+       *
+       * The font-size and font-family values are required. If other values are
+       * missing; a default, if it exist, will be used.
+       */
+       case _fontPartFont:
+         var processor = new ExpressionsProcessor(exprs);
+         return _mergeFontStyles(processor.processFont(), dartStyles);
+      case _fontPartFamily:
+        var processor = new ExpressionsProcessor(exprs);
+
+        try {
+          return _mergeFontStyles(processor.processFontFamily(), dartStyles);
+        } catch (fontException) {
+          _error(fontException, _peekToken.span);
+        }
+        break;
+      case _fontPartSize:
+        var processor = new ExpressionsProcessor(exprs);
+        return _mergeFontStyles(processor.processFontSize(), dartStyles);
+      case _fontPartStyle:
+        /* Possible style values:
+         *   normal [default]
+         *   italic
+         *   oblique
+         *   inherit
+         */
+        // TODO(terry): TBD
+        break;
+      case _fontPartVariant:
+        /* Possible variant values:
+         *   normal  [default]
+         *   small-caps
+         *   inherit
+         */
+        // TODO(terry): TBD
+        break;
+      case _fontPartWeight:
+        /* Possible weight values:
+         *   normal [default]
+         *   bold
+         *   bolder
+         *   lighter
+         *   100 - 900
+         *   inherit
+         */
+        // TODO(terry): Only 'normal', 'bold', or values of 100-900 supoorted
+        //              need to handle bolder, lighter, and inherit.  See
+        //              https://github.com/dart-lang/csslib/issues/1
+        var expr = exprs.expressions[0];
+        if (expr is NumberTerm) {
+          var fontExpr = new FontExpression(expr.span,
+              weight: expr.value);
+          return _mergeFontStyles(fontExpr, dartStyles);
+        } else if (expr is LiteralTerm) {
+          int weight = _nameToFontWeight[expr.value.toString()];
+          if (weight != null) {
+            var fontExpr = new FontExpression(expr.span, weight: weight);
+            return _mergeFontStyles(fontExpr, dartStyles);
+          }
+        }
+        break;
+      case _lineHeightPart:
+        num lineHeight;
+        if (exprs.expressions.length == 1) {
+          var expr = exprs.expressions[0];
+          if (expr is UnitTerm) {
+            UnitTerm unitTerm = expr;
+            // TODO(terry): Need to handle other units and LiteralTerm normal
+            //              See https://github.com/dart-lang/csslib/issues/2.
+            if (unitTerm.unit == TokenKind.UNIT_LENGTH_PX ||
+                   unitTerm.unit == TokenKind.UNIT_LENGTH_PT) {
+              var fontExpr = new FontExpression(expr.span,
+                  lineHeight: new LineHeight(expr.value, inPixels: true));
+              return _mergeFontStyles(fontExpr, dartStyles);
+            } else if (isChecked) {
+              _warning("Unexpected unit for line-height", expr.span);
+            }
+          } else if (expr is NumberTerm) {
+            var fontExpr = new FontExpression(expr.span,
+                lineHeight: new LineHeight(expr.value, inPixels: false));
+            return _mergeFontStyles(fontExpr, dartStyles);
+          } else if (isChecked) {
+            _warning("Unexpected value for line-height", expr.span);
+          }
+        }
+        break;
+      case _marginPartMargin:
+        return new MarginExpression.boxEdge(exprs.span, processFourNums(exprs));
+      case _borderPartBorder:
+        for (var expr in exprs.expressions) {
+          var v = marginValue(expr);
+          if (v != null) {
+            final box = new BoxEdge.uniform(v);
+            return new BorderExpression.boxEdge(exprs.span, box);
+          }
+        }
+        break;
+      case _borderPartWidth:
+        var v = marginValue(exprs.expressions[0]);
+        if (v != null) {
+          final box = new BoxEdge.uniform(v);
+          return new BorderExpression.boxEdge(exprs.span, box);
+        }
+        break;
+      case _paddingPartPadding:
+        return new PaddingExpression.boxEdge(exprs.span,
+            processFourNums(exprs));
+      case _marginPartLeft:
+      case _marginPartTop:
+      case _marginPartRight:
+      case _marginPartBottom:
+      case _borderPartLeft:
+      case _borderPartTop:
+      case _borderPartRight:
+      case _borderPartBottom:
+      case _borderPartLeftWidth:
+      case _borderPartTopWidth:
+      case _borderPartRightWidth:
+      case _borderPartBottomWidth:
+      case _heightPart:
+      case _widthPart:
+      case _paddingPartLeft:
+      case _paddingPartTop:
+      case _paddingPartRight:
+      case _paddingPartBottom:
+        if (exprs.expressions.length > 0) {
+          return processOneNumber(exprs, styleType);
+        }
+        break;
+      default:
+        // Don't handle it.
+        return;
+    }
+  }
+
+  // TODO(terry): Look at handling width of thin, thick, etc. any none numbers
+  //              to convert to a number.
+  processOneNumber(Expressions exprs, int part) {
+    var value = marginValue(exprs.expressions[0]);
+    if (value != null) {
+      switch (part) {
+        case _marginPartLeft:
+          return new MarginExpression(exprs.span, left: value);
+        case _marginPartTop:
+          return new MarginExpression(exprs.span, top: value);
+        case _marginPartRight:
+          return new MarginExpression(exprs.span, right: value);
+        case _marginPartBottom:
+          return new MarginExpression(exprs.span, bottom: value);
+        case _borderPartLeft:
+        case _borderPartLeftWidth:
+          return new BorderExpression(exprs.span, left: value);
+        case _borderPartTop:
+        case _borderPartTopWidth:
+          return new BorderExpression(exprs.span, top: value);
+        case _borderPartRight:
+        case _borderPartRightWidth:
+          return new BorderExpression(exprs.span, right: value);
+        case _borderPartBottom:
+        case _borderPartBottomWidth:
+          return new BorderExpression(exprs.span, bottom: value);
+        case _heightPart:
+          return new HeightExpression(exprs.span, value);
+        case _widthPart:
+          return new WidthExpression(exprs.span, value);
+        case _paddingPartLeft:
+          return new PaddingExpression(exprs.span, left: value);
+        case _paddingPartTop:
+          return new PaddingExpression(exprs.span, top: value);
+        case _paddingPartRight:
+          return new PaddingExpression(exprs.span, right: value);
+        case _paddingPartBottom:
+          return new PaddingExpression(exprs.span, bottom: value);
+      }
+    }
+  }
+
+  /**
+   * Margins are of the format:
+   *
+   *   top,right,bottom,left      (4 parameters)
+   *   top,right/left, bottom     (3 parameters)
+   *   top/bottom,right/left      (2 parameters)
+   *   top/right/bottom/left      (1 parameter)
+   *
+   * The values of the margins can be a unit or unitless or auto.
+   */
+  processFourNums(Expressions exprs) {
+    num top;
+    num right;
+    num bottom;
+    num left;
+
+    int totalExprs = exprs.expressions.length;
+    switch (totalExprs) {
+      case 1:
+        top = marginValue(exprs.expressions[0]);
+        right = top;
+        bottom = top;
+        left = top;
+        break;
+      case 2:
+        top = marginValue(exprs.expressions[0]);
+        bottom = top;
+        right = marginValue(exprs.expressions[1]);
+        left = right;
+       break;
+      case 3:
+        top = marginValue(exprs.expressions[0]);
+        right = marginValue(exprs.expressions[1]);
+        left = right;
+        bottom = marginValue(exprs.expressions[2]);
+        break;
+      case 4:
+        top = marginValue(exprs.expressions[0]);
+        right = marginValue(exprs.expressions[1]);
+        bottom = marginValue(exprs.expressions[2]);
+        left = marginValue(exprs.expressions[3]);
+        break;
+      default:
+        return;
+    }
+
+    return new BoxEdge.clockwiseFromTop(top, right, bottom, left);
+  }
+
+  // TODO(terry): Need to handle auto.
+  marginValue(var exprTerm) {
+    if (exprTerm is UnitTerm || exprTerm is NumberTerm) {
+      return exprTerm.value;
+    }
+  }
+
+  //  Expression grammar:
+  //
+  //  expression:   term [ operator? term]*
+  //
+  //  operator:     '/' | ','
+  //  term:         (see processTerm)
+  //
+  processExpr([bool ieFilter = false]) {
+    int start = _peekToken.start;
+    Expressions expressions = new Expressions(_makeSpan(start));
+
+    bool keepGoing = true;
+    var expr;
+    while (keepGoing && (expr = processTerm(ieFilter)) != null) {
+      var op;
+
+      int opStart = _peekToken.start;
+
+      switch (_peek()) {
+      case TokenKind.SLASH:
+        op = new OperatorSlash(_makeSpan(opStart));
+        break;
+      case TokenKind.COMMA:
+        op = new OperatorComma(_makeSpan(opStart));
+        break;
+      case TokenKind.BACKSLASH:
+        // Backslash outside of string; detected IE8 or older signaled by \9 at
+        // end of an expression.
+        var ie8Start = _peekToken.start;
+
+        _next();
+        if (_peekKind(TokenKind.INTEGER)) {
+          var numToken = _next();
+          var value = int.parse(numToken.text);
+          if (value == 9) {
+            op = new IE8Term(_makeSpan(ie8Start));
+          } else if (isChecked) {
+            _warning("\$value is not valid in an expression", _makeSpan(start));
+          }
+        }
+        break;
+      }
+
+      if (expr != null) {
+        expressions.add(expr);
+      } else {
+        keepGoing = false;
+      }
+
+      if (op != null) {
+        expressions.add(op);
+        if (op is IE8Term) {
+          keepGoing = false;
+        } else {
+          _next();
+        }
+      }
+    }
+
+    return expressions;
+  }
+
+  static int MAX_UNICODE = int.parse('0x10FFFF');
+
+  //  Term grammar:
+  //
+  //  term:
+  //    unary_operator?
+  //    [ term_value ]
+  //    | STRING S* | IDENT S* | URI S* | UNICODERANGE S* | hexcolor
+  //
+  //  term_value:
+  //    NUMBER S* | PERCENTAGE S* | LENGTH S* | EMS S* | EXS S* | ANGLE S* |
+  //    TIME S* | FREQ S* | function
+  //
+  //  NUMBER:       {num}
+  //  PERCENTAGE:   {num}%
+  //  LENGTH:       {num}['px' | 'cm' | 'mm' | 'in' | 'pt' | 'pc']
+  //  EMS:          {num}'em'
+  //  EXS:          {num}'ex'
+  //  ANGLE:        {num}['deg' | 'rad' | 'grad']
+  //  TIME:         {num}['ms' | 's']
+  //  FREQ:         {num}['hz' | 'khz']
+  //  function:     IDENT '(' expr ')'
+  //
+  processTerm([bool ieFilter = false]) {
+    int start = _peekToken.start;
+    Token t;                          // token for term's value
+    var value;                        // value of term (numeric values)
+
+    var unary = "";
+    switch (_peek()) {
+    case TokenKind.HASH:
+      this._eat(TokenKind.HASH);
+      if (!_anyWhiteSpaceBeforePeekToken(TokenKind.HASH)) {
+        String hexText;
+        if (_peekKind(TokenKind.INTEGER)) {
+          String hexText1 = _peekToken.text;
+          _next();
+          if (_peekIdentifier()) {
+            hexText = '$hexText1${identifier().name}';
+          } else {
+            hexText = hexText1;
+          }
+        } else if (_peekIdentifier()) {
+          hexText = identifier().name;
+        }
+        if (hexText != null) {
+          return _parseHex(hexText, _makeSpan(start));
+        }
+      }
+
+      if (isChecked) {
+        _warning("Expected hex number", _makeSpan(start));
+      }
+      // Construct the bad hex value with a #<space>number.
+      return _parseHex(" ${processTerm().text}", _makeSpan(start));
+    case TokenKind.INTEGER:
+      t = _next();
+      value = int.parse("${unary}${t.text}");
+      break;
+    case TokenKind.DOUBLE:
+      t = _next();
+      value = double.parse("${unary}${t.text}");
+      break;
+    case TokenKind.SINGLE_QUOTE:
+    case TokenKind.DOUBLE_QUOTE:
+      value = processQuotedString(false);
+      value = '"${_escapeString(value)}"';
+      return new LiteralTerm(value, value, _makeSpan(start));
+    case TokenKind.LPAREN:
+      _next();
+
+      GroupTerm group = new GroupTerm(_makeSpan(start));
+
+      var term;
+      do {
+        term = processTerm();
+        if (term != null && term is LiteralTerm) {
+          group.add(term);
+        }
+      } while (term != null && !_maybeEat(TokenKind.RPAREN) &&
+          !isPrematureEndOfFile());
+
+      return group;
+    case TokenKind.LBRACK:
+      _next();
+
+      var term = processTerm();
+      if (!(term is NumberTerm)) {
+        _error('Expecting a positive number', _makeSpan(start));
+      }
+
+      _eat(TokenKind.RBRACK);
+
+      return new ItemTerm(term.value, term.text, _makeSpan(start));
+    case TokenKind.IDENTIFIER:
+      var nameValue = identifier();   // Snarf up the ident we'll remap, maybe.
+
+      if (!ieFilter && _maybeEat(TokenKind.LPAREN)) {
+        // FUNCTION
+        return processFunction(nameValue);
+      } if (ieFilter) {
+         if (_maybeEat(TokenKind.COLON) &&
+           nameValue.name.toLowerCase() == 'progid') {
+           // IE filter:progid:
+           return processIEFilter(start);
+         } else {
+           // Handle filter:<name> where name is any filter e.g., alpha, chroma,
+           // Wave, blur, etc.
+           return processIEFilter(start);
+         }
+      }
+
+      // TODO(terry): Need to have a list of known identifiers today only
+      //              'from' is special.
+      if (nameValue.name == 'from') {
+        return new LiteralTerm(nameValue, nameValue.name, _makeSpan(start));
+      }
+
+      // What kind of identifier is it, named color?
+      var colorEntry = TokenKind.matchColorName(nameValue.name);
+      if (colorEntry == null) {
+        if (isChecked) {
+          var propName = nameValue.name;
+          var errMsg = TokenKind.isPredefinedName(propName) ?
+              "Improper use of property value ${propName}" :
+              "Unknown property value ${propName}";
+          _warning(errMsg, _makeSpan(start));
+        }
+        return new LiteralTerm(nameValue, nameValue.name, _makeSpan(start));
+      }
+
+      // Yes, process the color as an RGB value.
+      String rgbColor = TokenKind.decimalToHex(
+          TokenKind.colorValue(colorEntry), 6);
+      return _parseHex(rgbColor, _makeSpan(start));
+    case TokenKind.UNICODE_RANGE:
+      var first;
+      var second;
+      var firstNumber;
+      var secondNumber;
+      _eat(TokenKind.UNICODE_RANGE, unicodeRange: true);
+      if (_maybeEat(TokenKind.HEX_INTEGER, unicodeRange: true)) {
+        first = _previousToken.text;
+        firstNumber = int.parse('0x$first');
+        if (firstNumber > MAX_UNICODE) {
+          _error("unicode range must be less than 10FFFF", _makeSpan(start));
+        }
+        if (_maybeEat(TokenKind.MINUS, unicodeRange: true)) {
+          if (_maybeEat(TokenKind.HEX_INTEGER, unicodeRange: true)) {
+            second = _previousToken.text;
+            secondNumber = int.parse('0x$second');
+            if (secondNumber > MAX_UNICODE) {
+              _error("unicode range must be less than 10FFFF",
+                  _makeSpan(start));
+            }
+            if (firstNumber > secondNumber) {
+              _error("unicode first range can not be greater than last",
+                  _makeSpan(start));
+            }
+          }
+        }
+      } else if (_maybeEat(TokenKind.HEX_RANGE, unicodeRange: true)) {
+        first = _previousToken.text;
+      }
+
+      return new UnicodeRangeTerm(first, second, _makeSpan(start));
+    case TokenKind.AT:
+      if (messages.options.lessSupport) {
+        _next();
+
+        var expr = processExpr();
+        if (isChecked && expr.expressions.length > 1) {
+          _error("only @name for Less syntax", _peekToken.span);
+        }
+
+        var param = expr.expressions[0];
+        return new VarUsage(param.text, [], _makeSpan(start));
+      }
+      break;
+    }
+
+    return processDimension(t, value, _makeSpan(start));
+  }
+
+  /** Process all dimension units. */
+  processDimension(Token t, var value, Span span) {
+    var term;
+    var unitType = this._peek();
+
+    switch (unitType) {
+    case TokenKind.UNIT_EM:
+      term = new EmTerm(value, t.text, span);
+      _next();    // Skip the unit
+      break;
+    case TokenKind.UNIT_EX:
+      term = new ExTerm(value, t.text, span);
+      _next();    // Skip the unit
+      break;
+    case TokenKind.UNIT_LENGTH_PX:
+    case TokenKind.UNIT_LENGTH_CM:
+    case TokenKind.UNIT_LENGTH_MM:
+    case TokenKind.UNIT_LENGTH_IN:
+    case TokenKind.UNIT_LENGTH_PT:
+    case TokenKind.UNIT_LENGTH_PC:
+      term = new LengthTerm(value, t.text, span, unitType);
+      _next();    // Skip the unit
+      break;
+    case TokenKind.UNIT_ANGLE_DEG:
+    case TokenKind.UNIT_ANGLE_RAD:
+    case TokenKind.UNIT_ANGLE_GRAD:
+    case TokenKind.UNIT_ANGLE_TURN:
+      term = new AngleTerm(value, t.text, span, unitType);
+      _next();    // Skip the unit
+      break;
+    case TokenKind.UNIT_TIME_MS:
+    case TokenKind.UNIT_TIME_S:
+      term = new TimeTerm(value, t.text, span, unitType);
+      _next();    // Skip the unit
+      break;
+    case TokenKind.UNIT_FREQ_HZ:
+    case TokenKind.UNIT_FREQ_KHZ:
+      term = new FreqTerm(value, t.text, span, unitType);
+      _next();    // Skip the unit
+      break;
+    case TokenKind.PERCENT:
+      term = new PercentageTerm(value, t.text, span);
+      _next();    // Skip the %
+      break;
+    case TokenKind.UNIT_FRACTION:
+      term = new FractionTerm(value, t.text, span);
+      _next();     // Skip the unit
+      break;
+    case TokenKind.UNIT_RESOLUTION_DPI:
+    case TokenKind.UNIT_RESOLUTION_DPCM:
+    case TokenKind.UNIT_RESOLUTION_DPPX:
+      term = new ResolutionTerm(value, t.text, span, unitType);
+      _next();    // Skip the unit
+      break;
+    case TokenKind.UNIT_CH:
+      term = new ChTerm(value, t.text, span, unitType);
+      _next();    // Skip the unit
+      break;
+    case TokenKind.UNIT_REM:
+      term = new RemTerm(value, t.text, span, unitType);
+      _next();    // Skip the unit
+      break;
+    case TokenKind.UNIT_VIEWPORT_VW:
+    case TokenKind.UNIT_VIEWPORT_VH:
+    case TokenKind.UNIT_VIEWPORT_VMIN:
+    case TokenKind.UNIT_VIEWPORT_VMAX:
+      term = new ViewportTerm(value, t.text, span, unitType);
+      _next();    // Skip the unit
+      break;
+    default:
+      if (value != null && t != null) {
+        term = (value is Identifier)
+            ? new LiteralTerm(value, value.name, span)
+            : new NumberTerm(value, t.text, span);
+      }
+      break;
+    }
+
+    return term;
+  }
+
+  processQuotedString([bool urlString = false]) {
+    int start = _peekToken.start;
+
+    // URI term sucks up everything inside of quotes(' or ") or between parens
+    int stopToken = urlString ? TokenKind.RPAREN : -1;
+    switch (_peek()) {
+    case TokenKind.SINGLE_QUOTE:
+      stopToken = TokenKind.SINGLE_QUOTE;
+      start = _peekToken.start + 1;   // Skip the quote might have whitespace.
+      _next();    // Skip the SINGLE_QUOTE.
+      break;
+    case TokenKind.DOUBLE_QUOTE:
+      stopToken = TokenKind.DOUBLE_QUOTE;
+      start = _peekToken.start + 1;   // Skip the quote might have whitespace.
+      _next();    // Skip the DOUBLE_QUOTE.
+      break;
+    default:
+      if (urlString) {
+        if (_peek() == TokenKind.LPAREN) {
+          _next();    // Skip the LPAREN.
+          start = _peekToken.start;
+        }
+        stopToken = TokenKind.RPAREN;
+      } else {
+        _error('unexpected string', _makeSpan(start));
+      }
+      break;
+    }
+
+    // Gobble up everything until we hit our stop token.
+    int runningStart = _peekToken.start;
+    while (_peek() != stopToken && _peek() != TokenKind.END_OF_FILE) {
+      var tok = _next();
+    }
+
+    // All characters between quotes is the string.
+    int end = _peekToken.end;
+    var stringValue = (_peekToken.span as FileSpan).file.getText(start,
+        end - 1);
+
+    if (stopToken != TokenKind.RPAREN) {
+      _next();    // Skip the SINGLE_QUOTE or DOUBLE_QUOTE;
+    }
+
+    return stringValue;
+  }
+
+  // TODO(terry): Should probably understand IE's non-standard filter syntax to
+  //              fully support calc, var(), etc.
+  /**
+   * IE's filter property breaks CSS value parsing.  IE's format can be:
+   *
+   *    filter: progid:DXImageTransform.MS.gradient(Type=0, Color='#9d8b83');
+   *
+   * We'll just parse everything after the 'progid:' look for the left paren
+   * then parse to the right paren ignoring everything in between.
+   */
+  processIEFilter(int startAfterProgidColon) {
+    int parens = 0;
+
+    while (_peek() != TokenKind.END_OF_FILE) {
+      switch (_peek()) {
+        case TokenKind.LPAREN:
+          _eat(TokenKind.LPAREN);
+          parens++;
+          break;
+        case TokenKind.RPAREN:
+          _eat(TokenKind.RPAREN);
+          if (--parens == 0) {
+            var tok = tokenizer.makeIEFilter(startAfterProgidColon,
+                _peekToken.start);
+            return new LiteralTerm(tok.text, tok.text, tok.span);
+          }
+          break;
+        default:
+          _eat(_peek());
+      }
+    }
+  }
+
+  //  Function grammar:
+  //
+  //  function:     IDENT '(' expr ')'
+  //
+  processFunction(Identifier func) {
+    int start = _peekToken.start;
+
+    String name = func.name;
+
+    switch (name) {
+    case 'url':
+      // URI term sucks up everything inside of quotes(' or ") or between parens
+      String urlParam = processQuotedString(true);
+
+      // TODO(terry): Better error messge and checking for mismatched quotes.
+      if (_peek() == TokenKind.END_OF_FILE) {
+        _error("problem parsing URI", _peekToken.span);
+      }
+
+      if (_peek() == TokenKind.RPAREN) {
+        _next();
+      }
+
+      return new UriTerm(urlParam, _makeSpan(start));
+    case 'calc':
+      // TODO(terry): Implement expression handling...
+      break;
+    case 'var':
+      // TODO(terry): Consider handling var in IE specific filter/progid.  This
+      //              will require parsing entire IE specific syntax e.g.,
+      //              param = value or progid:com_id, etc. for example:
+      //
+      //    var-blur: Blur(Add = 0, Direction = 225, Strength = 10);
+      //    var-gradient: progid:DXImageTransform.Microsoft.gradient"
+      //      (GradientType=0,StartColorStr='#9d8b83', EndColorStr='#847670');
+      var expr = processExpr();
+      if (!_maybeEat(TokenKind.RPAREN)) {
+        _error("problem parsing var expected ), ", _peekToken.span);
+      }
+      if (isChecked &&
+          expr.expressions.where((e) => e is OperatorComma).length > 1) {
+        _error("too many parameters to var()", _peekToken.span);
+      }
+
+      var paramName = expr.expressions[0].text;
+
+      // [0] - var name, [1] - OperatorComma, [2] - default value.
+      var defaultValues = expr.expressions.length >= 3
+          ? expr.expressions.sublist(2) : [];
+      return new VarUsage(paramName, defaultValues, _makeSpan(start));
+    default:
+      var expr = processExpr();
+      if (!_maybeEat(TokenKind.RPAREN)) {
+        _error("problem parsing function expected ), ", _peekToken.span);
+      }
+
+      return new FunctionTerm(name, name, expr, _makeSpan(start));
+    }
+
+    return null;
+  }
+
+  identifier() {
+    var tok = _next();
+
+    if (!TokenKind.isIdentifier(tok.kind) &&
+        !TokenKind.isKindIdentifier(tok.kind)) {
+      if (isChecked) {
+        _warning('expected identifier, but found $tok', tok.span);
+      }
+      return new Identifier("", _makeSpan(tok.start));
+    }
+
+    return new Identifier(tok.text, _makeSpan(tok.start));
+  }
+
+  // TODO(terry): Move this to base <= 36 and into shared code.
+  static int _hexDigit(int c) {
+    if(c >= 48/*0*/ && c <= 57/*9*/) {
+      return c - 48;
+    } else if (c >= 97/*a*/ && c <= 102/*f*/) {
+      return c - 87;
+    } else if (c >= 65/*A*/ && c <= 70/*F*/) {
+      return c - 55;
+    } else {
+      return -1;
+    }
+  }
+
+  HexColorTerm _parseHex(String hexText, Span span) {
+    int hexValue = 0;
+
+     for (int i = 0; i < hexText.length; i++) {
+      var digit = _hexDigit(hexText.codeUnitAt(i));
+      if (digit < 0) {
+        _warning('Bad hex number', span);
+        return new HexColorTerm(new BAD_HEX_VALUE(), hexText, span);
+      }
+      hexValue = (hexValue << 4) + digit;
+    }
+
+    // Make 3 character hex value #RRGGBB => #RGB iff:
+    // high/low nibble of RR is the same, high/low nibble of GG is the same and
+    // high/low nibble of BB is the same.
+    if (hexText.length == 6 &&
+        hexText[0] == hexText[1] &&
+        hexText[2] == hexText[3] &&
+        hexText[4] == hexText[5]) {
+      hexText = '${hexText[0]}${hexText[2]}${hexText[4]}';
+    } else if (hexText.length == 4 &&
+        hexText[0] == hexText[1] &&
+        hexText[2] == hexText[3]) {
+      hexText = '${hexText[0]}${hexText[2]}';
+    } else if (hexText.length == 2 && hexText[0] == hexText[1]) {
+      hexText = '${hexText[0]}';
+    }
+    return new HexColorTerm(hexValue, hexText, span);
+  }
+}
+
+class ExpressionsProcessor {
+  final Expressions _exprs;
+  int _index = 0;
+
+  ExpressionsProcessor(this._exprs);
+
+  // TODO(terry): Only handles ##px unit.
+  processFontSize() {
+    /* font-size[/line-height]
+     *
+     * Possible size values:
+     *   xx-small
+     *   small
+     *   medium [default]
+     *   large
+     *   x-large
+     *   xx-large
+     *   smaller
+     *   larger
+     *   ##length in px, pt, etc.
+     *   ##%, percent of parent elem's font-size
+     *   inherit
+     */
+    LengthTerm size;
+    LineHeight lineHt;
+    bool nextIsLineHeight = false;
+    for (; _index < _exprs.expressions.length; _index++) {
+      var expr = _exprs.expressions[_index];
+      if (size == null && expr is LengthTerm) {
+        // font-size part.
+        size = expr;
+      } else if (size != null) {
+        if (expr is OperatorSlash) {
+          // LineHeight could follow?
+          nextIsLineHeight = true;
+        } else if (nextIsLineHeight && expr is LengthTerm) {
+          assert(expr.unit == TokenKind.UNIT_LENGTH_PX);
+          lineHt = new LineHeight(expr.value, inPixels: true);
+          nextIsLineHeight = false;
+          _index++;
+          break;
+        } else {
+          break;
+        }
+      } else {
+        break;
+      }
+    }
+
+    return new FontExpression(_exprs.span, size: size, lineHeight: lineHt);
+  }
+
+  processFontFamily() {
+    final List<String> family = <String>[];
+
+    /* Possible family values:
+     * font-family: arial, Times new roman ,Lucida Sans Unicode,Courier;
+     * font-family: "Times New Roman", arial, Lucida Sans Unicode, Courier;
+     */
+    bool moreFamilies = false;
+
+    for (; _index < _exprs.expressions.length; _index++) {
+      Expression expr = _exprs.expressions[_index];
+      if (expr is LiteralTerm) {
+        if (family.length == 0 || moreFamilies) {
+          // It's font-family now.
+          family.add(expr.toString());
+          moreFamilies = false;
+        } else if (isChecked) {
+          messages.warning('Only font-family can be a list', _exprs.span);
+        }
+      } else if (expr is OperatorComma && family.length > 0) {
+        moreFamilies = true;
+      } else {
+        break;
+      }
+    }
+
+    return new FontExpression(_exprs.span, family: family);
+  }
+
+  processFont() {
+    var family;
+
+    // Process all parts of the font expression.
+    FontExpression fontSize;
+    FontExpression fontFamily;
+    for (; _index < _exprs.expressions.length; _index++) {
+      var expr = _exprs.expressions[_index];
+      // Order is font-size font-family
+      if (fontSize == null) {
+        fontSize = processFontSize();
+      }
+      if (fontFamily == null) {
+        fontFamily = processFontFamily();
+      }
+      //TODO(terry): Handle font-weight, font-style, and font-variant. See
+      //               https://github.com/dart-lang/csslib/issues/3
+      //               https://github.com/dart-lang/csslib/issues/4
+      //               https://github.com/dart-lang/csslib/issues/5
+    }
+
+    return new FontExpression(_exprs.span,
+        size: fontSize.font.size,
+        lineHeight: fontSize.font.lineHeight,
+        family: fontFamily.font.family);
+  }
+}
+
+/**
+ * Escapes [text] for use in a CSS string.
+ * [single] specifies single quote `'` vs double quote `"`.
+ */
+String _escapeString(String text, {bool single: false}) {
+  StringBuffer result = null;
+
+  for (int i = 0; i < text.length; i++) {
+    int code = text.codeUnitAt(i);
+    var replace = null;
+    switch (code) {
+      case 34/*'"'*/:  if (!single) replace = r'\"'; break;
+      case 39/*"'"*/:  if (single) replace = r"\'"; break;
+    }
+
+    if (replace != null && result == null) {
+      result = new StringBuffer(text.substring(0, i));
+    }
+
+    if (result != null) result.write(replace != null ? replace : text[i]);
+  }
+
+  return result == null ? text : result.toString();
+}