anchor.diff:          // Make sure that copies of [complex] retain their status as "original"
           // selectors. This includes selectors that are modified because a :not()
           // was extended into.
  -        if (first && _original[complex] != null) {
  -          _original[outputComplex] = true;
  +        if (first && _originals.contains(complex)) {
  +          _originals.add(outputComplex);
           }
           first = false;
   
  
positive.code:   CssStyleRule addSelector(CssValue<SelectorList> selector, FileSpan span,
        [List<CssMediaQuery> mediaContext]) {
      for (var complex in selector.value.components) {
        _original[complex] = true;
      }
  
      if (_extensions.isNotEmpty) {
  
negative.code:   /// extensions.
    final _extensions = <SimpleSelector, Map<ComplexSelector, Extension>>{};
  
    /// A map from CSS rules to the media query contexts they're defined in.
    ///
    /// This tracks the contexts in which each style rule is defined. If a rule is
    /// defined at the top level, it doesn't have an entry.
    final _mediaContexts = new Map<CssStyleRule, List<CssMediaQuery>>();
  
    /// A map from [SimpleSelector]s to the specificity of their source
    /// selectors.
    ///
    /// This tracks the maximum specificity of the [ComplexSelector] that
    /// originally contained each [SimpleSelector]. This allows us to ensure that
  