code: function StyleSheet(el) {
          /**
       * style/link element or selector
       * @cfg {HTMLElement|String} el
       */
          /**
       * style/link element
       * @type {HTMLElement}
       * @property el
       */
          if (el.el) {
              el = el.el;
          }
          el = this.el = Dom.get(el);    // http://msdn.microsoft.com/en-us/library/ie/ms535871(v=vs.85).aspx
                                         // firefox 跨域时抛出异常
          // http://msdn.microsoft.com/en-us/library/ie/ms535871(v=vs.85).aspx
          // firefox 跨域时抛出异常
          var sheet = el.sheet || el.styleSheet;
          this.sheet = sheet;
          var cssRules = {};
          this.cssRules = cssRules;
          var rulesName = sheet && 'cssRules' in sheet ? 'cssRules' : 'rules';
          this.rulesName = rulesName;
          var domCssRules = sheet[rulesName];
          var i, rule, selectorText, styleDeclaration;
          for (i = domCssRules.length - 1; i >= 0; i--) {
              rule = domCssRules[i];
              selectorText = rule.selectorText;    // 去重
              // 去重
              if (styleDeclaration = cssRules[selectorText]) {
                  styleDeclaration.style.cssText += ';' + styleDeclaration.style.cssText;
                  deleteRule(sheet, i);
              } else {
                  cssRules[selectorText] = rule;
              }
          }
      }
docs: Normalize operation about stylesheet
  @class KISSY.StyleSheet
  @param el {HTMLElement} style/link element
   
  Normalize operation about stylesheet
  @class KISSY.StyleSheet
  @param el {HTMLElement} style/link element