anchor.diff:  
     void visitStyleRule(StyleRule node) {
       var selectorText = _performInterpolation(node.selector, trim: true);
  -    if (_styleRules.isNotEmpty) {
  +    if (_styleRule != null) {
         // TODO: semantically resolve parent references.
         selectorText = new CssValue(
  -          "${_styleRules.last.selector.value} ${selectorText.value}",
  +          "${_styleRule.selector.value} ${selectorText.value}",
             span: node.selector.span);
       }
   
  
positive.code: 
        if (_innerChildren.isNotEmpty) {
          _outerChildren.addFirst(new LinkedListValue(new CssStyleRule(
              _styleRules.last.selector,
              _innerChildren.map((node) => node.value),
              span: _styleRules.last.span)));
        }
  
        return _outerChildren.map((node) => node.value);
  
negative.code:   final Environment _environment;
    final PerformExpressionVisitor _expressionVisitor;
  
    /// The innermost containing style rule, if one exists.
    CssStyleRule _styleRule;
  
    /// The children of the root stylesheet node.
    ///
  