anchor.diff:      } else if (condition is SupportsNegation) {
         return "not ${_parenthesize(condition.condition)}";
       } else if (condition is SupportsInterpolation) {
  -      return condition.expression.accept(this).toCssString(quote: false);
  +      return _evaluateToCss(condition.expression, quote: false);
       } else if (condition is SupportsDeclaration) {
  -      return "(${condition.name.accept(this).toCssString()}: "
  -          "${condition.value.accept(this).toCssString()})";
  +      return "(${_evaluateToCss(condition.name)}: "
  +          "${_evaluateToCss(condition.value)})";
       } else {
         return null;
       }
  
positive.code:     var url = _interpolationToValue(import.url);
      var supports = import.supports;
      var resolvedSupports = supports is SupportsDeclaration
          ? "(${supports.name.accept(this).toCssString()}: "
              "${supports.value.accept(this).toCssString()})"
          : (supports == null ? null : _visitSupportsCondition(supports));
      var mediaQuery =
          import.media == null ? null : _visitMediaQueries(import.media);
  
negative.code:     return new SassString(
          node.text.contents.map((value) {
            if (value is String) return value;
            var expression = value as Expression;
            var result = expression.accept(this);
            return result is SassString
                ? result.text
                : _toCss(result, expression.span, quote: false);
          }).join(),
          quotes: node.hasQuotes);
    }
  