docs: function compatibleStyleSheetInsertRule(rule, index){
      // fetch selector and style from rule description
      var m = rule.match(/^([^{]+)\{(.*)\}\s*$/);
      if (m)
      {
        var selectors = m[1].trim().split(/\s*,\s*/);
        for (var i = 0; i < selectors.length; i++)
          this.addRule(selectors[i], m[2] || null, index++);
        return index - 1;
      }
  
      /** @cut */ throw new Error('Syntax error in CSS rule to be added');
    }