[html5lib] implement querySelector/querySelectorAll

pkg/csslib/lib/src/tree.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.
 
 part of csslib.visitor;
 
 /////////////////////////////////////////////////////////////////////////
 // CSS specific types:
 /////////////////////////////////////////////////////////////////////////
 
 class Identifier extends TreeNode {
   String name;
 
   Identifier(this.name, Span span): super(span);
 
   Identifier clone() => new Identifier(name, span);
 
-  void visit(VisitorBase visitor) => visitor.visitIdentifier(this);
+  visit(VisitorBase visitor) => visitor.visitIdentifier(this);
 
   String toString() => name;
 }
 
 class Wildcard extends TreeNode {
   Wildcard(Span span): super(span);
   Wildcard clone() => new Wildcard(span);
-  void visit(VisitorBase visitor) => visitor.visitWildcard(this);
+  visit(VisitorBase visitor) => visitor.visitWildcard(this);
 
   String get name => '*';
 }
 
 class ThisOperator extends TreeNode {
   ThisOperator(Span span): super(span);
   ThisOperator clone() => new ThisOperator(span);
-  void visit(VisitorBase visitor) => visitor.visitThisOperator(this);
+  visit(VisitorBase visitor) => visitor.visitThisOperator(this);
 
   String get name => '&';
 }
 
 class Negation extends TreeNode {
   Negation(Span span): super(span);
   Negation clone() => new Negation(span);
-  void visit(VisitorBase visitor) => visitor.visitNegation(this);
+  visit(VisitorBase visitor) => visitor.visitNegation(this);
 
   String get name => 'not';
 }
 
 // /*  ....   */
 class CssComment extends TreeNode {
   final String comment;
 
   CssComment(this.comment, Span span): super(span);
   CssComment clone() => new CssComment(comment, span);
-  void visit(VisitorBase visitor) => visitor.visitCssComment(this);
+  visit(VisitorBase visitor) => visitor.visitCssComment(this);
 }
 
 // CDO/CDC (Comment Definition Open <!-- and Comment Definition Close -->).
 class CommentDefinition extends CssComment {
   CommentDefinition(String comment, Span span): super(comment, span);
   CommentDefinition clone() => new CommentDefinition(comment, span);
-  void visit(VisitorBase visitor) => visitor.visitCommentDefinition(this);
+  visit(VisitorBase visitor) => visitor.visitCommentDefinition(this);
 }
 
 class SelectorGroup extends TreeNode {
   final List<Selector> selectors;
 
   SelectorGroup(this.selectors, Span span): super(span);
 
   SelectorGroup clone() => new SelectorGroup(selectors, span);
 
-  void visit(VisitorBase visitor) => visitor.visitSelectorGroup(this);
+  visit(VisitorBase visitor) => visitor.visitSelectorGroup(this);
 }
 
 class Selector extends TreeNode {
   final List<SimpleSelectorSequence> simpleSelectorSequences;
 
   Selector(this.simpleSelectorSequences, Span span) : super(span);
 
   void add(SimpleSelectorSequence seq) => simpleSelectorSequences.add(seq);
 
   int get length => simpleSelectorSequences.length;
 
   Selector clone() {
     var simpleSequences = simpleSelectorSequences
         .map((ss) => ss.clone())
         .toList();
 
     return new Selector(simpleSequences, span);
   }
 
-  void visit(VisitorBase visitor) => visitor.visitSelector(this);
+  visit(VisitorBase visitor) => visitor.visitSelector(this);
 }
 
 class SimpleSelectorSequence extends TreeNode {
   /** +, >, ~, NONE */
   int combinator;
   final SimpleSelector simpleSelector;
 
   SimpleSelectorSequence(this.simpleSelector, Span span,
       [int combinator = TokenKind.COMBINATOR_NONE])
       : combinator = combinator, super(span);
 
   bool get isCombinatorNone => combinator == TokenKind.COMBINATOR_NONE;
   bool get isCombinatorPlus => combinator == TokenKind.COMBINATOR_PLUS;
   bool get isCombinatorGreater => combinator == TokenKind.COMBINATOR_GREATER;
   bool get isCombinatorTilde => combinator == TokenKind.COMBINATOR_TILDE;
   bool get isCombinatorDescendant =>
       combinator == TokenKind.COMBINATOR_DESCENDANT;
 
   String get _combinatorToString =>
       isCombinatorDescendant ? ' ' :
           isCombinatorPlus ? ' + ' :
               isCombinatorGreater ? ' > ' :
                   isCombinatorTilde ? ' ~ ' : '';
 
   SimpleSelectorSequence clone() =>
       new SimpleSelectorSequence(simpleSelector, span, combinator);
 
-  void visit(VisitorBase visitor) => visitor.visitSimpleSelectorSequence(this);
+  visit(VisitorBase visitor) => visitor.visitSimpleSelectorSequence(this);
 
   String toString() => simpleSelector.name;
 }
 
 /* All other selectors (element, #id, .class, attribute, pseudo, negation,
  * namespace, *) are derived from this selector.
  */
 abstract class SimpleSelector extends TreeNode {
   final _name; // Wildcard, ThisOperator, Identifier, Negation, others?
 
   SimpleSelector(this._name, Span span) : super(span);
 
   String get name => _name.name;
 
   bool get isWildcard => _name is Wildcard;
 
   bool get isThis => _name is ThisOperator;
 
-  void visit(VisitorBase visitor) => visitor.visitSimpleSelector(this);
+  visit(VisitorBase visitor) => visitor.visitSimpleSelector(this);
 }
 
 // element name
 class ElementSelector extends SimpleSelector {
   ElementSelector(name, Span span) : super(name, span);
-  void visit(VisitorBase visitor) => visitor.visitElementSelector(this);
+  visit(VisitorBase visitor) => visitor.visitElementSelector(this);
 
   ElementSelector clone() => new ElementSelector(_name, span);
 
   String toString() => name;
 }
 
 // namespace|element
 class NamespaceSelector extends SimpleSelector {
   final _namespace;           // null, Wildcard or Identifier
 
   NamespaceSelector(this._namespace, var name, Span span) : super(name, span);
 
   String get namespace =>
       _namespace is Wildcard ? '*' : _namespace == null ? '' : _namespace.name;
 
   bool get isNamespaceWildcard => _namespace is Wildcard;
 
   SimpleSelector get nameAsSimpleSelector => _name;
 
   NamespaceSelector clone() => new NamespaceSelector(_namespace, "", span);
 
-  void visit(VisitorBase visitor) => visitor.visitNamespaceSelector(this);
+  visit(VisitorBase visitor) => visitor.visitNamespaceSelector(this);
 
   String toString() => "$namespace|${nameAsSimpleSelector.name}";
 }
 
 // [attr op value]
 class AttributeSelector extends SimpleSelector {
   final int _op;
   final _value;
 
   AttributeSelector(Identifier name, this._op, this._value,
       Span span) : super(name, span);
 
+  int get operatorKind => _op;
+
+  get value => _value;
+
   String matchOperator() {
     switch (_op) {
     case TokenKind.EQUALS:
       return '=';
     case TokenKind.INCLUDES:
       return '~=';
     case TokenKind.DASH_MATCH:
       return '|=';
     case TokenKind.PREFIX_MATCH:
       return '^=';
@@ skipping 31 matching lines @@
       } else {
         return '"${_value}"';
       }
     } else {
       return '';
     }
   }
 
   AttributeSelector clone() => new AttributeSelector(_name, _op, _value, span);
 
-  void visit(VisitorBase visitor) => visitor.visitAttributeSelector(this);
+  visit(VisitorBase visitor) => visitor.visitAttributeSelector(this);
 
   String toString() => "[$name${matchOperator()}${valueToString()}]";
 }
 
 // #id
 class IdSelector extends SimpleSelector {
   IdSelector(Identifier name, Span span) : super(name, span);
   IdSelector clone() => new IdSelector(_name, span);
-  void visit(VisitorBase visitor) => visitor.visitIdSelector(this);
+  visit(VisitorBase visitor) => visitor.visitIdSelector(this);
 
   String toString() => "#$_name";
 }
 
 // .class
 class ClassSelector extends SimpleSelector {
   ClassSelector(Identifier name, Span span) : super(name, span);
   ClassSelector clone() => new ClassSelector(_name, span);
-  void visit(VisitorBase visitor) => visitor.visitClassSelector(this);
+  visit(VisitorBase visitor) => visitor.visitClassSelector(this);
 
   String toString() => ".$_name";
 }
 
 // :pseudoClass
 class PseudoClassSelector extends SimpleSelector {
   PseudoClassSelector(Identifier name, Span span) : super(name, span);
-  void visit(VisitorBase visitor) => visitor.visitPseudoClassSelector(this);
+  visit(VisitorBase visitor) => visitor.visitPseudoClassSelector(this);
 
   PseudoClassSelector clone() => new PseudoClassSelector(_name, span);
 
   String toString() => ":$name";
 }
 
 // ::pseudoElement
 class PseudoElementSelector extends SimpleSelector {
   PseudoElementSelector(Identifier name, Span span) : super(name, span);
-  void visit(VisitorBase visitor) => visitor.visitPseudoElementSelector(this);
+  visit(VisitorBase visitor) => visitor.visitPseudoElementSelector(this);
 
   PseudoElementSelector clone() => new PseudoElementSelector(_name, span);
 
   String toString() => "::$name";
 }
 
 // :pseudoClassFunction(expression)
 class PseudoClassFunctionSelector extends PseudoClassSelector {
   final SelectorExpression expression;
 
   PseudoClassFunctionSelector(Identifier name, this.expression, Span span)
       : super(name, span);
 
   PseudoClassFunctionSelector clone() =>
       new PseudoClassFunctionSelector(_name, expression, span);
 
-  void visit(VisitorBase visitor) =>
+  visit(VisitorBase visitor) =>
       visitor.visitPseudoClassFunctionSelector(this);
 }
 
 // ::pseudoElementFunction(expression)
 class PseudoElementFunctionSelector extends PseudoElementSelector {
   final SelectorExpression expression;
 
   PseudoElementFunctionSelector(Identifier name, this.expression, Span span)
       : super(name, span);
 
   PseudoElementFunctionSelector clone() =>
       new PseudoElementFunctionSelector(_name, expression, span);
 
-  void visit(VisitorBase visitor) =>
+  visit(VisitorBase visitor) =>
       visitor.visitPseudoElementFunctionSelector(this);
 }
 
 class SelectorExpression extends TreeNode {
-  final List<Expression> expressions = [];
+  final List<Expression> expressions;
 
-  SelectorExpression(Span span): super(span);
+  SelectorExpression(this.expressions, Span span): super(span);
 
-  void add(Expression expression) {
-    expressions.add(expression);
+  SelectorExpression clone() {
+    return new SelectorExpression(
+        expressions.map((e) => e.clone()).toList(), span);
   }
 
-  SelectorExpression clone() {
-    var selectorExpr = new SelectorExpression(span);
-    for (var expr in expressions) {
-      selectorExpr.add(expr.clone());
-    }
-    return selectorExpr;
-  }
-
-  void visit(VisitorBase visitor) => visitor.visitSelectorExpression(this);
+  visit(VisitorBase visitor) => visitor.visitSelectorExpression(this);
 }
 
 // :NOT(negation_arg)
 class NegationSelector extends SimpleSelector {
   final SimpleSelector negationArg;
 
   NegationSelector(this.negationArg, Span span)
       : super(new Negation(span), span);
 
   NegationSelector clone() => new NegationSelector(negationArg, span);
 
-  void visit(VisitorBase visitor) => visitor.visitNegationSelector(this);
+  visit(VisitorBase visitor) => visitor.visitNegationSelector(this);
 }
 
 class NoOp extends TreeNode {
   NoOp() : super(null);
 
   NoOp clone() => new NoOp();
 
-  void visit(VisitorBase visitor) => visitor.visitNoOp(this);
+  visit(VisitorBase visitor) => visitor.visitNoOp(this);
 }
 
 class StyleSheet extends TreeNode {
   /**
    * Contains charset, ruleset, directives (media, page, etc.), and selectors.
    */
   final List<TreeNode> topLevels;
 
   StyleSheet(this.topLevels, Span span) : super(span) {
     for (final node in topLevels) {
       assert(node is TopLevelProduction || node is Directive);
     }
   }
 
   /** Selectors only in this tree. */
   StyleSheet.selector(this.topLevels, Span span) : super(span);
 
   StyleSheet clone() {
     var clonedTopLevels = topLevels.map((e) => e.clone()).toList();
     return new StyleSheet(clonedTopLevels, span);
   }
 
-  void visit(VisitorBase visitor) => visitor.visitStyleSheet(this);
+  visit(VisitorBase visitor) => visitor.visitStyleSheet(this);
 }
 
 class TopLevelProduction extends TreeNode {
   TopLevelProduction(Span span) : super(span);
   TopLevelProduction clone() => new TopLevelProduction(span);
-  void visit(VisitorBase visitor) => visitor.visitTopLevelProduction(this);
+  visit(VisitorBase visitor) => visitor.visitTopLevelProduction(this);
 }
 
 class RuleSet extends TopLevelProduction {
   final SelectorGroup _selectorGroup;
   final DeclarationGroup _declarationGroup;
 
   RuleSet(this._selectorGroup, this._declarationGroup, Span span) : super(span);
 
   SelectorGroup get selectorGroup => _selectorGroup;
   DeclarationGroup get declarationGroup => _declarationGroup;
 
   RuleSet clone() {
     var cloneSelectorGroup = _selectorGroup.clone();
     var cloneDeclarationGroup = _declarationGroup.clone();
     return new RuleSet(cloneSelectorGroup, cloneDeclarationGroup, span);
   }
 
-  void visit(VisitorBase visitor) => visitor.visitRuleSet(this);
+  visit(VisitorBase visitor) => visitor.visitRuleSet(this);
 }
 
 class Directive extends TreeNode {
   Directive(Span span) : super(span);
 
   bool get isBuiltIn => true;       // Known CSS directive?
   bool get isExtension => false;    // SCSS extension?
 
   Directive clone() => new Directive(span);
-  void visit(VisitorBase visitor) => visitor.visitDirective(this);
+  visit(VisitorBase visitor) => visitor.visitDirective(this);
 }
 
 class ImportDirective extends Directive {
   /** import name specified. */
   final String import;
 
   /** Any media queries for this import. */
   final List<MediaQuery> mediaQueries;
 
   ImportDirective(this.import, this.mediaQueries, Span span) : super(span);
 
   ImportDirective clone() {
     var cloneMediaQueries = [];
     for (var mediaQuery in mediaQueries) {
       cloneMediaQueries.add(mediaQuery.clone());
     }
     return new ImportDirective(import, cloneMediaQueries, span);
   }
 
-  void visit(VisitorBase visitor) => visitor.visitImportDirective(this);
+  visit(VisitorBase visitor) => visitor.visitImportDirective(this);
 }
 
 /**
  *  MediaExpression grammar:
  *    '(' S* media_feature S* [ ':' S* expr ]? ')' S*
  */
 class MediaExpression extends TreeNode {
   final bool andOperator;
   final Identifier _mediaFeature;
   final Expressions exprs;
 
   MediaExpression(this.andOperator, this._mediaFeature, this.exprs, Span span)
       : super(span);
 
   String get mediaFeature => _mediaFeature.name;
 
   MediaExpression clone() {
     var clonedExprs = exprs.clone();
     return new MediaExpression(andOperator, _mediaFeature, clonedExprs, span);
   }
 
-  void visit(VisitorBase visitor) => visitor.visitMediaExpression(this);
+  visit(VisitorBase visitor) => visitor.visitMediaExpression(this);
 }
 
 /**
  * MediaQuery grammar:
  *    : [ONLY | NOT]? S* media_type S* [ AND S* media_expression ]*
  *    | media_expression [ AND S* media_expression ]*
  *   media_type
  *    : IDENT
  *   media_expression
  *    : '(' S* media_feature S* [ ':' S* expr ]? ')' S*
@@ skipping 16 matching lines @@
   String get unary =>
       TokenKind.idToValue(TokenKind.MEDIA_OPERATORS, _mediaUnary).toUpperCase();
 
   MediaQuery clone() {
     var cloneExpressions = [];
     for (var expr in expressions) {
       cloneExpressions.add(expr.clone());
     }
     return new MediaQuery(_mediaUnary, _mediaType, cloneExpressions, span);
   }
-  void visit(VisitorBase visitor) => visitor.visitMediaQuery(this);
+  visit(VisitorBase visitor) => visitor.visitMediaQuery(this);
 }
 
 class MediaDirective extends Directive {
   final List<MediaQuery> mediaQueries;
   final List<RuleSet> rulesets;
 
   MediaDirective(this.mediaQueries, this.rulesets, Span span) : super(span);
 
   MediaDirective clone() {
     var cloneQueries = [];
     for (var mediaQuery in mediaQueries) {
       cloneQueries.add(mediaQuery.clone());
     }
     var cloneRulesets = [];
     for (var ruleset in rulesets) {
       cloneRulesets.add(ruleset.clone());
     }
     return new MediaDirective(cloneQueries, cloneRulesets, span);
   }
 
-  void visit(VisitorBase visitor) => visitor.visitMediaDirective(this);
+  visit(VisitorBase visitor) => visitor.visitMediaDirective(this);
 }
 
 class HostDirective extends Directive {
   final List<RuleSet> rulesets;
 
   HostDirective(this.rulesets, Span span) : super(span);
 
   HostDirective clone() {
     var cloneRulesets = [];
     for (var ruleset in rulesets) {
       cloneRulesets.add(ruleset.clone());
     }
     return new HostDirective(cloneRulesets, span);
   }
 
-  void visit(VisitorBase visitor) => visitor.visitHostDirective(this);
+  visit(VisitorBase visitor) => visitor.visitHostDirective(this);
 }
 
 class PageDirective extends Directive {
   final String _ident;
   final String _pseudoPage;
   final List<DeclarationGroup> _declsMargin;
 
   PageDirective(this._ident, this._pseudoPage, this._declsMargin,
       Span span) : super(span);
 
   PageDirective clone() {
     var cloneDeclsMargin = [];
     for (var declMargin in _declsMargin) {
       cloneDeclsMargin.add(declMargin.clone());
     }
     return new PageDirective(_ident, _pseudoPage, cloneDeclsMargin, span);
   }
 
-  void visit(VisitorBase visitor) => visitor.visitPageDirective(this);
+  visit(VisitorBase visitor) => visitor.visitPageDirective(this);
 
   bool get hasIdent => _ident != null && _ident.length > 0;
   bool get hasPseudoPage => _pseudoPage != null && _pseudoPage.length > 0;
 }
 
 class CharsetDirective extends Directive {
   final String charEncoding;
 
   CharsetDirective(this.charEncoding, Span span) : super(span);
   CharsetDirective clone() => new CharsetDirective(charEncoding, span);
-  void visit(VisitorBase visitor) => visitor.visitCharsetDirective(this);
+  visit(VisitorBase visitor) => visitor.visitCharsetDirective(this);
 }
 
 class KeyFrameDirective extends Directive {
   /*
    * Either @keyframe or keyframe prefixed with @-webkit-, @-moz-, @-ms-, @-o-.
    */
   final int _keyframeName;
   final name;
   final List<KeyFrameBlock> _blocks;
 
@@ skipping 15 matching lines @@
     }
   }
 
   KeyFrameDirective clone() {
     var cloneBlocks = [];
     for (var block in _blocks) {
       cloneBlocks.add(block.clone());
     }
     return new KeyFrameDirective(_keyframeName, cloneBlocks, span);
   }
-  void visit(VisitorBase visitor) => visitor.visitKeyFrameDirective(this);
+  visit(VisitorBase visitor) => visitor.visitKeyFrameDirective(this);
 }
 
 class KeyFrameBlock extends Expression {
   final Expressions _blockSelectors;
   final DeclarationGroup _declarations;
 
   KeyFrameBlock(this._blockSelectors, this._declarations, Span span)
       : super(span);
 
   KeyFrameBlock clone() =>
       new KeyFrameBlock(_blockSelectors.clone(), _declarations.clone(), span);
-  void visit(VisitorBase visitor) => visitor.visitKeyFrameBlock(this);
+  visit(VisitorBase visitor) => visitor.visitKeyFrameBlock(this);
 }
 
 class FontFaceDirective extends Directive {
   final DeclarationGroup _declarations;
 
   FontFaceDirective(this._declarations, Span span) : super(span);
 
   FontFaceDirective clone() =>
       new FontFaceDirective(_declarations.clone(), span);
-  void visit(VisitorBase visitor) => visitor.visitFontFaceDirective(this);
+  visit(VisitorBase visitor) => visitor.visitFontFaceDirective(this);
 }
 
 class StyletDirective extends Directive {
   final String dartClassName;
   final List<RuleSet> rulesets;
 
   StyletDirective(this.dartClassName, this.rulesets, Span span) : super(span);
 
   bool get isBuiltIn => false;
   bool get isExtension => true;
 
   StyletDirective clone() {
     var cloneRulesets = [];
     for (var ruleset in rulesets) {
       cloneRulesets.add(ruleset.clone());
     }
     return new StyletDirective(dartClassName, cloneRulesets, span);
   }
 
-  void visit(VisitorBase visitor) => visitor.visitStyletDirective(this);
+  visit(VisitorBase visitor) => visitor.visitStyletDirective(this);
 }
 
 class NamespaceDirective extends Directive {
   /** Namespace prefix. */
   final String _prefix;
 
   /** URI associated with this namespace. */
   final String _uri;
 
   NamespaceDirective(this._prefix, this._uri, Span span) : super(span);
 
   NamespaceDirective clone() => new NamespaceDirective(_prefix, _uri, span);
 
-  void visit(VisitorBase visitor) => visitor.visitNamespaceDirective(this);
+  visit(VisitorBase visitor) => visitor.visitNamespaceDirective(this);
 
   String get prefix => _prefix.length > 0 ? '$_prefix ' : '';
 }
 
 /** To support Less syntax @name: expression */
 class VarDefinitionDirective extends Directive {
   final VarDefinition def;
 
   VarDefinitionDirective(this.def, Span span) : super(span);
 
   VarDefinitionDirective clone() =>
       new VarDefinitionDirective(def.clone(), span);
 
-  void visit(VisitorBase visitor) => visitor.visitVarDefinitionDirective(this);
+  visit(VisitorBase visitor) => visitor.visitVarDefinitionDirective(this);
 }
 
 class MixinDefinition extends Directive {
   final String name;
   final List definedArgs;
   final bool varArgs;
 
   MixinDefinition(this.name, this.definedArgs, this.varArgs, Span span)
       : super(span);
 
   MixinDefinition clone() {
     var cloneDefinedArgs = [];
     for (var definedArg in definedArgs) {
       cloneDefinedArgs.add(definedArg.clone());
     }
     return new MixinDefinition(name, cloneDefinedArgs, varArgs, span);
   }
 
-  void visit(VisitorBase visitor) => visitor.visitMixinDefinition(this);
+  visit(VisitorBase visitor) => visitor.visitMixinDefinition(this);
 }
 
 /** Support a Sass @mixin. See http://sass-lang.com for description. */
 class MixinRulesetDirective extends MixinDefinition {
   final List<RuleSet> rulesets;
 
   MixinRulesetDirective(String name, List<VarDefinitionDirective> args,
       bool varArgs, this.rulesets, Span span) :
       super(name, args, varArgs, span);
 
   MixinRulesetDirective clone() {
     var clonedArgs = [];
     for (var arg in definedArgs) {
       clonedArgs.add(arg.clone());
     }
     var clonedRulesets = [];
     for (var ruleset in rulesets) {
       clonedRulesets.add(ruleset.clone());
     }
     return new MixinRulesetDirective(name, clonedArgs, varArgs, clonedRulesets,
         span);
   }
 
-  void visit(VisitorBase visitor) => visitor.visitMixinRulesetDirective(this);
+  visit(VisitorBase visitor) => visitor.visitMixinRulesetDirective(this);
 }
 
 class MixinDeclarationDirective extends MixinDefinition {
   final DeclarationGroup declarations;
 
   MixinDeclarationDirective(String name, List<VarDefinitionDirective>  args,
       bool varArgs, this.declarations, Span span) :
       super(name, args, varArgs, span);
 
   MixinDeclarationDirective clone() {
     var clonedArgs = [];
     for (var arg in definedArgs) {
       clonedArgs.add(arg.clone());
     }
     return new MixinDeclarationDirective(name, clonedArgs, varArgs,
         declarations.clone(), span);
   }
 
-  void visit(VisitorBase visitor) => visitor.visitMixinDeclarationDirective(this);
+  visit(VisitorBase visitor) => visitor.visitMixinDeclarationDirective(this);
 }
 
 /** To support consuming a SASS mixin @include. */
 class IncludeDirective extends Directive {
   final String name;
   final List<List<TreeNode>> args;
 
   IncludeDirective(this.name, this.args, Span span) : super(span);
 
   IncludeDirective clone() {
     var cloneArgs = [];
     for (var arg in args) {
       for (var term in arg) {
         cloneArgs.add(term.clone());
       }
     }
     return new IncludeDirective(name, cloneArgs, span);
   }
 
-  void visit(VisitorBase visitor) => visitor.visitIncludeDirective(this);
+  visit(VisitorBase visitor) => visitor.visitIncludeDirective(this);
 }
 
 /** To support SASS @content. */
 class ContentDirective extends Directive {
   ContentDirective(Span span) : super(span);
 
-  void visit(VisitorBase visitor) => visitor.visitContentDirective(this);
+  visit(VisitorBase visitor) => visitor.visitContentDirective(this);
 }
 
 class Declaration extends TreeNode {
   final Identifier _property;
   final Expression _expression;
   /** Style exposed to Dart. */
   dynamic dartStyle;
   final bool important;
 
   /**
@@ skipping 12 matching lines @@
 
   String get property => isIE7 ? '*${_property.name}' : _property.name;
   Expression get expression => _expression;
 
   bool get hasDartStyle => dartStyle != null;
 
   Declaration clone() =>
       new Declaration(_property.clone(), _expression.clone(), dartStyle, span,
       important: important);
 
-  void visit(VisitorBase visitor) => visitor.visitDeclaration(this);
+  visit(VisitorBase visitor) => visitor.visitDeclaration(this);
 }
 
 // TODO(terry): Consider 2 kinds of VarDefinitions static at top-level and
 //              dynamic when in a declaration.  Currently, Less syntax
 //              '@foo: expression' and 'var-foo: expression' in a declaration
 //              are statically resolved. Better solution, if @foo or var-foo
 //              are top-level are then statically resolved and var-foo in a
 //              declaration group (surrounded by a selector) would be dynamic.
 class VarDefinition extends Declaration {
   bool badUsage = false;
 
   VarDefinition(Identifier definedName, Expression expr, Span span)
       : super(definedName, expr, null, span);
 
   String get definedName => _property.name;
 
   VarDefinition clone() =>
       new VarDefinition(_property.clone(),
       expression != null ? expression.clone() : null, span);
 
-  void visit(VisitorBase visitor) => visitor.visitVarDefinition(this);
+  visit(VisitorBase visitor) => visitor.visitVarDefinition(this);
 }
 
 /**
  * Node for usage of @include mixin[(args,...)] found in a declaration group
  * instead of at a ruleset (toplevel) e.g.,
  * div {
  *   @include mixin1;
  * }
  */
 class IncludeMixinAtDeclaration extends Declaration {
   final IncludeDirective include;
 
   IncludeMixinAtDeclaration(this.include, Span span)
       : super(null, null, null, span);
 
   IncludeMixinAtDeclaration clone() =>
       new IncludeMixinAtDeclaration(include.clone(), span);
 
-  void visit(VisitorBase visitor) =>
+  visit(VisitorBase visitor) =>
       visitor.visitIncludeMixinAtDeclaration(this);
 }
 
 class ExtendDeclaration extends Declaration {
   final List<TreeNode> selectors;
 
   ExtendDeclaration(this.selectors, Span span) :
       super(null, null, null, span);
 
   ExtendDeclaration clone() {
     var newSelector = selectors.map((s) => s.clone()).toList();
     return new ExtendDeclaration(newSelector, span);
   }
 
-  void visit(VisitorBase visitor) => visitor.visitExtendDeclaration(this);
+  visit(VisitorBase visitor) => visitor.visitExtendDeclaration(this);
 }
 
 class DeclarationGroup extends TreeNode {
   /** Can be either Declaration or RuleSet (if nested selector). */
   final List declarations;
 
   DeclarationGroup(this.declarations, Span span) : super(span);
 
   DeclarationGroup clone() {
     var clonedDecls = declarations.map((d) => d.clone()).toList();
     return new DeclarationGroup(clonedDecls, span);
   }
 
-  void visit(VisitorBase visitor) => visitor.visitDeclarationGroup(this);
+  visit(VisitorBase visitor) => visitor.visitDeclarationGroup(this);
 }
 
 class MarginGroup extends DeclarationGroup {
   final int margin_sym;       // TokenType for for @margin sym.
 
   MarginGroup(this.margin_sym, List<Declaration> decls, Span span)
       : super(decls, span);
   MarginGroup clone() =>
     new MarginGroup(margin_sym, super.clone() as dynamic, span);
-  void visit(VisitorBase visitor) => visitor.visitMarginGroup(this);
+  visit(VisitorBase visitor) => visitor.visitMarginGroup(this);
 }
 
 class VarUsage extends Expression {
   final String name;
   final List<Expression> defaultValues;
 
   VarUsage(this.name, this.defaultValues, Span span) : super(span);
 
   VarUsage clone() {
     var clonedValues = [];
     for (var expr in defaultValues) {
       clonedValues.add(expr.clone());
     }
     return new VarUsage(name, clonedValues, span);
   }
 
-  void visit(VisitorBase visitor) => visitor.visitVarUsage(this);
+  visit(VisitorBase visitor) => visitor.visitVarUsage(this);
 }
 
 class OperatorSlash extends Expression {
   OperatorSlash(Span span) : super(span);
   OperatorSlash clone() => new OperatorSlash(span);
-  void visit(VisitorBase visitor) => visitor.visitOperatorSlash(this);
+  visit(VisitorBase visitor) => visitor.visitOperatorSlash(this);
 }
 
 class OperatorComma extends Expression {
   OperatorComma(Span span) : super(span);
   OperatorComma clone() => new OperatorComma(span);
-  void visit(VisitorBase visitor) => visitor.visitOperatorComma(this);
+  visit(VisitorBase visitor) => visitor.visitOperatorComma(this);
 }
 
 class OperatorPlus extends Expression {
   OperatorPlus(Span span) : super(span);
   OperatorPlus clone() => new OperatorPlus(span);
-  void visit(VisitorBase visitor) => visitor.visitOperatorPlus(this);
+  visit(VisitorBase visitor) => visitor.visitOperatorPlus(this);
 }
 
 class OperatorMinus extends Expression {
   OperatorMinus(Span span) : super(span);
   OperatorMinus clone() => new OperatorMinus(span);
-  void visit(VisitorBase visitor) => visitor.visitOperatorMinus(this);
+  visit(VisitorBase visitor) => visitor.visitOperatorMinus(this);
 }
 
 class UnicodeRangeTerm extends Expression {
   final String first;
   final String second;
 
   UnicodeRangeTerm(this.first, this.second, Span span) : super(span);
 
   bool get hasSecond => second != null;
 
   UnicodeRangeTerm clone() => new UnicodeRangeTerm(first, second, span);
 
-  void visit(VisitorBase visitor) => visitor.visitUnicodeRangeTerm(this);
+  visit(VisitorBase visitor) => visitor.visitUnicodeRangeTerm(this);
 }
 
 class LiteralTerm extends Expression {
   // TODO(terry): value and text fields can be made final once all CSS resources
   //              are copied/symlink'd in the build tool and UriVisitor in
   //              web_ui is removed.
   dynamic value;
   String text;
 
   LiteralTerm(this.value, this.text, Span span) : super(span);
 
   LiteralTerm clone() => new LiteralTerm(value, text, span);
 
-  void visit(VisitorBase visitor) => visitor.visitLiteralTerm(this);
+  visit(VisitorBase visitor) => visitor.visitLiteralTerm(this);
 }
 
 class NumberTerm extends LiteralTerm {
   NumberTerm(value, String t, Span span) : super(value, t, span);
   NumberTerm clone() => new NumberTerm(value, text, span);
-  void visit(VisitorBase visitor) => visitor.visitNumberTerm(this);
+  visit(VisitorBase visitor) => visitor.visitNumberTerm(this);
 }
 
 class UnitTerm extends LiteralTerm {
   final int unit;
 
   UnitTerm(value, String t, Span span, this.unit) : super(value, t, span);
 
   UnitTerm clone() => new UnitTerm(value, text, span, unit);
 
-  void visit(VisitorBase visitor) => visitor.visitUnitTerm(this);
+  visit(VisitorBase visitor) => visitor.visitUnitTerm(this);
 
   String unitToString() => TokenKind.unitToString(unit);
 
   String toString() => '$text${unitToString()}';
 }
 
 class LengthTerm extends UnitTerm {
   LengthTerm(value, String t, Span span,
       [int unit = TokenKind.UNIT_LENGTH_PX]) : super(value, t, span, unit) {
     assert(this.unit == TokenKind.UNIT_LENGTH_PX ||
         this.unit == TokenKind.UNIT_LENGTH_CM ||
         this.unit == TokenKind.UNIT_LENGTH_MM ||
         this.unit == TokenKind.UNIT_LENGTH_IN ||
         this.unit == TokenKind.UNIT_LENGTH_PT ||
         this.unit == TokenKind.UNIT_LENGTH_PC);
   }
   LengthTerm clone() => new LengthTerm(value, text, span, unit);
-  void visit(VisitorBase visitor) => visitor.visitLengthTerm(this);
+  visit(VisitorBase visitor) => visitor.visitLengthTerm(this);
 }
 
 class PercentageTerm extends LiteralTerm {
   PercentageTerm(value, String t, Span span) : super(value, t, span);
   PercentageTerm clone() => new PercentageTerm(value, text, span);
-  void visit(VisitorBase visitor) => visitor.visitPercentageTerm(this);
+  visit(VisitorBase visitor) => visitor.visitPercentageTerm(this);
 }
 
 class EmTerm extends LiteralTerm {
   EmTerm(value, String t, Span span) : super(value, t, span);
   EmTerm clone() => new EmTerm(value, text, span);
-  void visit(VisitorBase visitor) => visitor.visitEmTerm(this);
+  visit(VisitorBase visitor) => visitor.visitEmTerm(this);
 }
 
 class ExTerm extends LiteralTerm {
   ExTerm(value, String t, Span span) : super(value, t, span);
   ExTerm clone() => new ExTerm(value, text, span);
-  void visit(VisitorBase visitor) => visitor.visitExTerm(this);
+  visit(VisitorBase visitor) => visitor.visitExTerm(this);
 }
 
 class AngleTerm extends UnitTerm {
   AngleTerm(var value, String t, Span span,
     [int unit = TokenKind.UNIT_LENGTH_PX]) : super(value, t, span, unit) {
     assert(this.unit == TokenKind.UNIT_ANGLE_DEG ||
         this.unit == TokenKind.UNIT_ANGLE_RAD ||
         this.unit == TokenKind.UNIT_ANGLE_GRAD ||
         this.unit == TokenKind.UNIT_ANGLE_TURN);
   }
 
   AngleTerm clone() => new AngleTerm(value, text, span, unit);
-  void visit(VisitorBase visitor) => visitor.visitAngleTerm(this);
+  visit(VisitorBase visitor) => visitor.visitAngleTerm(this);
 }
 
 class TimeTerm extends UnitTerm {
   TimeTerm(var value, String t, Span span,
     [int unit = TokenKind.UNIT_LENGTH_PX]) : super(value, t, span, unit) {
     assert(this.unit == TokenKind.UNIT_ANGLE_DEG ||
         this.unit == TokenKind.UNIT_TIME_MS ||
         this.unit == TokenKind.UNIT_TIME_S);
   }
 
   TimeTerm clone() => new TimeTerm(value, text, span, unit);
-  void visit(VisitorBase visitor) => visitor.visitTimeTerm(this);
+  visit(VisitorBase visitor) => visitor.visitTimeTerm(this);
 }
 
 class FreqTerm extends UnitTerm {
   FreqTerm(var value, String t, Span span,
     [int unit = TokenKind.UNIT_LENGTH_PX]) : super(value, t, span, unit) {
     assert(unit == TokenKind.UNIT_FREQ_HZ || unit == TokenKind.UNIT_FREQ_KHZ);
   }
 
   FreqTerm clone() => new FreqTerm(value, text, span, unit);
-  void visit(VisitorBase visitor) => visitor.visitFreqTerm(this);
+  visit(VisitorBase visitor) => visitor.visitFreqTerm(this);
 }
 
 class FractionTerm extends LiteralTerm {
   FractionTerm(var value, String t, Span span) : super(value, t, span);
 
   FractionTerm clone() => new FractionTerm(value, text, span);
-  void visit(VisitorBase visitor) => visitor.visitFractionTerm(this);
+  visit(VisitorBase visitor) => visitor.visitFractionTerm(this);
 }
 
 class UriTerm extends LiteralTerm {
   UriTerm(String value, Span span) : super(value, value, span);
 
   UriTerm clone() => new UriTerm(value, span);
-  void visit(VisitorBase visitor) => visitor.visitUriTerm(this);
+  visit(VisitorBase visitor) => visitor.visitUriTerm(this);
 }
 
 class ResolutionTerm extends UnitTerm {
   ResolutionTerm(var value, String t, Span span,
     [int unit = TokenKind.UNIT_LENGTH_PX]) : super(value, t, span, unit) {
     assert(unit == TokenKind.UNIT_RESOLUTION_DPI ||
         unit == TokenKind.UNIT_RESOLUTION_DPCM ||
         unit == TokenKind.UNIT_RESOLUTION_DPPX);
   }
 
   ResolutionTerm clone() => new ResolutionTerm(value, text, span, unit);
-  void visit(VisitorBase visitor) => visitor.visitResolutionTerm(this);
+  visit(VisitorBase visitor) => visitor.visitResolutionTerm(this);
 }
 
 class ChTerm extends UnitTerm {
   ChTerm(var value, String t, Span span,
     [int unit = TokenKind.UNIT_LENGTH_PX]) : super(value, t, span, unit) {
     assert(unit == TokenKind.UNIT_CH);
   }
 
   ChTerm clone() => new ChTerm(value, text, span, unit);
-  void visit(VisitorBase visitor) => visitor.visitChTerm(this);
+  visit(VisitorBase visitor) => visitor.visitChTerm(this);
 }
 
 class RemTerm extends UnitTerm {
   RemTerm(var value, String t, Span span,
     [int unit = TokenKind.UNIT_LENGTH_PX]) : super(value, t, span, unit) {
     assert(unit == TokenKind.UNIT_REM);
   }
 
   RemTerm clone() => new RemTerm(value, text, span, unit);
-  void visit(VisitorBase visitor) => visitor.visitRemTerm(this);
+  visit(VisitorBase visitor) => visitor.visitRemTerm(this);
 }
 
 class ViewportTerm extends UnitTerm {
   ViewportTerm(var value, String t, Span span,
     [int unit = TokenKind.UNIT_LENGTH_PX]) : super(value, t, span, unit) {
     assert(unit == TokenKind.UNIT_VIEWPORT_VW ||
         unit == TokenKind.UNIT_VIEWPORT_VH ||
         unit == TokenKind.UNIT_VIEWPORT_VMIN ||
         unit == TokenKind.UNIT_VIEWPORT_VMAX);
   }
 
   ViewportTerm clone() => new ViewportTerm(value, text, span, unit);
-  void visit(VisitorBase visitor) => visitor.visitViewportTerm(this);
+  visit(VisitorBase visitor) => visitor.visitViewportTerm(this);
 }
 
 /** Type to signal a bad hex value for HexColorTerm.value. */
 class BAD_HEX_VALUE { }
 
 class HexColorTerm extends LiteralTerm {
   HexColorTerm(var value, String t, Span span) : super(value, t, span);
 
   HexColorTerm clone() => new HexColorTerm(value, text, span);
-  void visit(VisitorBase visitor) => visitor.visitHexColorTerm(this);
+  visit(VisitorBase visitor) => visitor.visitHexColorTerm(this);
 }
 
 class FunctionTerm extends LiteralTerm {
   final Expressions _params;
 
   FunctionTerm(var value, String t, this._params, Span span)
       : super(value, t, span);
 
   FunctionTerm clone() => new FunctionTerm(value, text, _params.clone(), span);
-  void visit(VisitorBase visitor) => visitor.visitFunctionTerm(this);
+  visit(VisitorBase visitor) => visitor.visitFunctionTerm(this);
 }
 
 /**
  * A "\9" was encountered at the end of the expression and before a semi-colon.
  * This is an IE trick to ignore a property or value except by IE 8 and older
  * browsers.
  */
 class IE8Term extends LiteralTerm {
   IE8Term(Span span) : super('\\9', '\\9', span);
   IE8Term clone() => new IE8Term(span);
-  void visit(VisitorBase visitor) => visitor.visitIE8Term(this);
+  visit(VisitorBase visitor) => visitor.visitIE8Term(this);
 }
 
 class GroupTerm extends Expression {
   final List<LiteralTerm> _terms;
 
   GroupTerm(Span span) : _terms =  [], super(span);
 
   void add(LiteralTerm term) {
     _terms.add(term);
   }
 
   GroupTerm clone() => new GroupTerm(span);
-  void visit(VisitorBase visitor) => visitor.visitGroupTerm(this);
+  visit(VisitorBase visitor) => visitor.visitGroupTerm(this);
 }
 
 class ItemTerm extends NumberTerm {
   ItemTerm(var value, String t, Span span) : super(value, t, span);
 
   ItemTerm clone() => new ItemTerm(value, text, span);
-  void visit(VisitorBase visitor) => visitor.visitItemTerm(this);
+  visit(VisitorBase visitor) => visitor.visitItemTerm(this);
 }
 
 class Expressions extends Expression {
   final List<Expression> expressions = [];
 
   Expressions(Span span): super(span);
 
   void add(Expression expression) {
     expressions.add(expression);
   }
 
   Expressions clone() {
     var clonedExprs = new Expressions(span);
     for (var expr in expressions) {
       clonedExprs.add(expr.clone());
     }
     return clonedExprs;
   }
-  void visit(VisitorBase visitor) => visitor.visitExpressions(this);
+  visit(VisitorBase visitor) => visitor.visitExpressions(this);
 }
 
 class BinaryExpression extends Expression {
   final Token op;
   final Expression x;
   final Expression y;
 
   BinaryExpression(this.op, this.x, this.y, Span span): super(span);
 
   BinaryExpression clone() =>
       new BinaryExpression(op, x.clone(), y.clone(), span);
-  void visit(VisitorBase visitor) => visitor.visitBinaryExpression(this);
+  visit(VisitorBase visitor) => visitor.visitBinaryExpression(this);
 }
 
 class UnaryExpression extends Expression {
   final Token op;
   final Expression self;
 
   UnaryExpression(this.op, this.self, Span span): super(span);
 
   UnaryExpression clone() => new UnaryExpression(op, self.clone(), span);
-  void visit(VisitorBase visitor) => visitor.visitUnaryExpression(this);
+  visit(VisitorBase visitor) => visitor.visitUnaryExpression(this);
 }
 
 abstract class DartStyleExpression extends TreeNode {
   static const int unknownType = 0;
   static const int fontStyle = 1;
   static const int marginStyle = 2;
   static const int borderStyle = 3;
   static const int paddingStyle = 4;
   static const int heightStyle = 5;
   static const int widthStyle = 6;
@@ skipping 14 matching lines @@
   bool get isFont => _styleType == fontStyle;
   bool get isMargin => _styleType == marginStyle;
   bool get isBorder => _styleType == borderStyle;
   bool get isPadding => _styleType == paddingStyle;
   bool get isHeight => _styleType == heightStyle;
   bool get isWidth => _styleType == widthStyle;
   bool get isBoxExpression => isMargin || isBorder || isPadding;
 
   bool isSame(DartStyleExpression other) => this._styleType == other._styleType;
 
-  void visit(VisitorBase visitor) => visitor.visitDartStyleExpression(this);
+  visit(VisitorBase visitor) => visitor.visitDartStyleExpression(this);
 }
 
 class FontExpression extends DartStyleExpression {
   final Font font;
 
   //   font-style font-variant font-weight font-size/line-height font-family
   // TODO(terry): Only px/pt for now need to handle all possible units to
   //              support calc expressions on units.
   FontExpression(Span span, {dynamic size, List<String> family,
       int weight, String style, String variant, LineHeight lineHeight}) :
@@ skipping 19 matching lines @@
 
   FontExpression._merge(FontExpression x, FontExpression y, Span span)
       : super(DartStyleExpression.fontStyle, span),
         font = new Font.merge(x.font, y.font);
 
   FontExpression clone() =>
     new FontExpression(span, size: font.size, family: font.family,
         weight: font.weight, style: font.style, variant: font.variant,
         lineHeight: font.lineHeight);
 
-  void visit(VisitorBase visitor) => visitor.visitFontExpression(this);
+  visit(VisitorBase visitor) => visitor.visitFontExpression(this);
 }
 
 abstract class BoxExpression extends DartStyleExpression {
   final BoxEdge box;
 
   BoxExpression(int styleType, Span span, this.box)
       : super(styleType, span);
 
   /*
    * Merges give 2 DartStyleExpression (or derived from DartStyleExpression,
    * e.g., FontExpression, etc.) will merge if the two expressions are of the
    * same property name (implies same exact type e.g, FontExpression).
    */
   merged(BoxExpression newDartExpr);
 
-  void visit(VisitorBase visitor) => visitor.visitBoxExpression(this);
+  visit(VisitorBase visitor) => visitor.visitBoxExpression(this);
 
   String get formattedBoxEdge {
     if (box.top == box.left && box.top == box.bottom &&
         box.top== box.right) {
       return '.uniform(${box.top})';
     } else {
       var left = box.left == null ? 0 : box.left;
       var top = box.top == null ? 0 : box.top;
       var right = box.right == null ? 0 : box.right;
       var bottom = box.bottom == null ? 0 : box.bottom;
@@ skipping 27 matching lines @@
     return new MarginExpression._merge(x, y, y.span);
   }
 
   MarginExpression._merge(MarginExpression x, MarginExpression y, Span span)
       : super(x._styleType, span, new BoxEdge.merge(x.box, y.box));
 
   MarginExpression clone() =>
       new MarginExpression(span, top: box.top, right: box.right,
       bottom: box.bottom, left: box.left);
 
-  void visit(VisitorBase visitor) => visitor.visitMarginExpression(this);
+  visit(VisitorBase visitor) => visitor.visitMarginExpression(this);
 }
 
 class BorderExpression extends BoxExpression {
   /** Border expression ripped apart. */
   BorderExpression(Span span, {num top, num right, num bottom, num left})
       : super(DartStyleExpression.borderStyle, span,
               new BoxEdge(left, top, right, bottom));
 
   BorderExpression.boxEdge(Span span, BoxEdge box)
       : super(DartStyleExpression.borderStyle, span, box);
@@ skipping 15 matching lines @@
 
   BorderExpression._merge(BorderExpression x, BorderExpression y,
       Span span)
       : super(DartStyleExpression.borderStyle, span,
               new BoxEdge.merge(x.box, y.box));
 
   BorderExpression clone() =>
       new BorderExpression(span, top: box.top, right: box.right,
       bottom: box.bottom, left: box.left);
 
-  void visit(VisitorBase visitor) => visitor.visitBorderExpression(this);
+  visit(VisitorBase visitor) => visitor.visitBorderExpression(this);
 }
 
 class HeightExpression extends DartStyleExpression {
   final height;
 
   HeightExpression(Span span, this.height)
       : super(DartStyleExpression.heightStyle, span);
 
   merged(HeightExpression newHeightExpr) {
     if (this.isHeight && newHeightExpr.isHeight) {
       return newHeightExpr;
     }
 
     return null;
   }
 
   HeightExpression clone() => new HeightExpression(span, height);
-  void visit(VisitorBase visitor) => visitor.visitHeightExpression(this);
+  visit(VisitorBase visitor) => visitor.visitHeightExpression(this);
 }
 
 class WidthExpression extends DartStyleExpression {
   final width;
 
   WidthExpression(Span span, this.width)
       : super(DartStyleExpression.widthStyle, span);
 
   merged(WidthExpression newWidthExpr) {
     if (this.isWidth && newWidthExpr.isWidth) {
       return newWidthExpr;
     }
 
     return null;
   }
 
   WidthExpression clone() => new WidthExpression(span, width);
-  void visit(VisitorBase visitor) => visitor.visitWidthExpression(this);
+  visit(VisitorBase visitor) => visitor.visitWidthExpression(this);
 }
 
 class PaddingExpression extends BoxExpression {
   /** Padding expression ripped apart. */
   PaddingExpression(Span span, {num top, num right, num bottom, num left})
       : super(DartStyleExpression.paddingStyle, span,
               new BoxEdge(left, top, right, bottom));
 
   PaddingExpression.boxEdge(Span span, BoxEdge box)
       : super(DartStyleExpression.paddingStyle, span, box);
@@ skipping 13 matching lines @@
     return new PaddingExpression._merge(x, y, y.span);
   }
 
   PaddingExpression._merge(PaddingExpression x, PaddingExpression y, Span span)
       : super(DartStyleExpression.paddingStyle, span,
             new BoxEdge.merge(x.box, y.box));
 
   PaddingExpression clone() =>
       new PaddingExpression(span, top: box.top, right: box.right,
       bottom: box.bottom, left: box.left);
-  void visit(VisitorBase visitor) => visitor.visitPaddingExpression(this);
+  visit(VisitorBase visitor) => visitor.visitPaddingExpression(this);
 }