docs: function (sheet, selector, rule) {
              var index;
              if (sheet.insertRule) {
                  return sheet.insertRule(selector + '{' + rule + '}', sheet.cssRules.length);
              } else {
                  index = sheet.addRule(selector, rule, sheet.rules.length);
                  if (index < 0) {
                      index = sheet.rules.length - 1;
                  }
                  return index;
              }
          }