anchor.diff:        var color = colorsByName[lower];
         if (color != null) return new ColorExpression(color, identifier.span);
   
  -      var specialFunction = _trySpecialFunction(lower, identifier.span);
  +      var specialFunction = _trySpecialFunction(lower, start);
         if (specialFunction != null) return specialFunction;
       }
   
  
positive.code:         case $semicolon:
            break loop;
  
          default:
            if (next == null) break loop;
  
            // TODO: support url()
            buffer.writeCharCode(scanner.readChar());
            wroteNewline = false;
            break;
        }
  
negative.code:     scanner.expectChar($rparen);
      buffer.writeCharCode($rparen);
  
      return new StringExpression(buffer.interpolation(scanner.spanFrom(start)));
    }
  
    Interpolation _tryUrlContents(LineScannerState start) {
      var start = scanner.state;
      if (!scanner.scanChar($lparen)) return null;
      whitespace();
  
      // Match Ruby Sass's behavior: parse a raw URL() if possible, and if not
  