anchor.diff:      return new ImportRule(imports, scanner.spanFrom(start));
     }
   
  -  Import _importArgument() {
  +  /// Consumes an argument to an `@import` rule.
  +  ///
  +  /// [ruleStart] should point before the `@`.
  +  Import _importArgument(LineScannerState ruleStart) {
       var start = scanner.state;
       var next = scanner.peekChar();
       if (next == $u || next == $U) {
  
positive.code:     var imports = <Import>[];
      do {
        whitespace();
        imports.add(_importArgument());
        whitespace();
      } while (scanner.scanChar($comma));
      expectStatementSeparator();
  
negative.code:       return new StaticImport(interpolation, scanner.spanFrom(start),
            supports: queries?.item1, media: queries?.item2);
      } else if (_inControlDirective || _inMixin) {
        _disallowedAtRule(ruleStart);
        return null;
      } else {
        try {
  