创建一个div元素并插入到文档碎片中  处理xhtml风格标签  将elem包裹起来，并将包裹后的字符串作为div的innerHTML  如果包裹深度大于1，只留下第一层包裹元素  清除在ie6,7中空table标签自动加入的tbody  将在ie9以下浏览器中剔除的开头空白字符串作为div元素的第一个文本子节点  将elem重新赋值为div的子节点集合(nodeList对象),  移除本次循环中文档碎片中的div，保持下一次循环中干净的div元素　　　　

var nodeNames = "abbr|article|aside|audio|bdi|canvas|data|datalist|details|figcaption|figure|footer|" +          "header|hgroup|mark|meter|nav|output|progress|section|summary|time|video",      wrapMap = {          option: [ 1, "<select multiple='multiple'>", "</select>" ],          legend: [ 1, "<fieldset>", "</fieldset>" ],          thead: [ 1, "<table>", "</table>" ],          tr: [ 2, "<table><tbody>", "</tbody></table>" ],          td: [ 3, "<table><tbody><tr>", "</tr></tbody></table>" ],          col: [ 2, "<table><tbody></tbody><colgroup>", "</colgroup></table>" ],          area: [ 1, "<map>", "</map>" ],          _default: [ 0, "", "" ]      },      rxhtmlTag = /<(?!area|br|col|embed|hr|img|input|link|meta|param)(([\w:]+)[^>]*)\/>/gi,      rtagName = /<([\w:]+)/,      rtbody = /<tbody/i,      rhtml = /<|&#?\w+;/,      rleadingWhitespace = /^\s+/,      rcheckableType = /^(?:checkbox|radio)$/,      rscriptType = /\/(java|ecma)script/i;  // 设置复选框checkbox或单选框radio表单元素的默认选中状态  function fixDefaultChecked( elem ) {      if ( rcheckableType.test( elem.type ) ) {          elem.defaultChecked = elem.checked;      }  }  // 创建一个安全的文档碎片  function createSafeFragment( document ) {      var list = nodeNames.split( "|" ),      safeFrag = document.createDocumentFragment(); // ie6,7,8浏览器把safeFrage作为HTMLDocument类型      // 针对ie9以下浏览器      if ( safeFrag.createElement ) {          while ( list.length ) {              safeFrag.createElement(                  list.pop()              );          }      }      return safeFrag;  }  // 模拟ES5中Array的新功能  // 该函数API：http://www.css88.com/jqapi-1.8/#p=jQuery.grep  jQuery.extend({      grep: function( elems, callback, inv ) {          var retVal,              ret = [],              i = 0,              length = elems.length;          inv = !!inv;          // Go through the array, only saving the items          // that pass the validator function          for ( ; i < length; i++ ) {              retVal = !!callback( elems[ i ], i );              if ( inv !== retVal ) {                  ret.push( elems[ i ] );              }          }          return ret;      }               });

jQuery.extend({      clean: function( elems, context, fragment, scripts ) {          // 声明变量          var i, j, elem, tag, wrap, depth, div, hasBody, tbody, len, handleScript, jsTags,              safe = context === document && safeFragment,              ret = [];          // 确保变量context为文档根节点document          if ( !context || typeof context.createDocumentFragment === "undefined" ) {              context = document;          }          // Use the already-created safe fragment if context permits          for ( i = 0; (elem = elems[i]) != null; i++ ) {              // 如果elem为数字,则将其转换为字符串              if ( typeof elem === "number" ) {                  elem += "";              }              // 如果elem为undefined,跳出本次循环              if ( !elem ) {                  continue;              }              // Convert html string into DOM nodes              // 转换数组项(字符串)为DOM节点              if ( typeof elem === "string" ) {                  // 如果不存在html实体编号或标签,则创建文本节点                  if ( !rhtml.test( elem ) ) {                      elem = context.createTextNode( elem );                  }                  // 处理是html标签字符串的数组项                  else {                      // Ensure a safe container in which to render the html                      // safe为#document-fragment类型,在ie9以下浏览器中,safe为HTMLDocument类型节点,且nodeNames数组为空                      safe = safe || createSafeFragment( context );                      // 创建一个div元素并将其插入到文档碎片中                      div = context.createElement("div");                      safe.appendChild( div );                      // Fix "XHTML"-style tags in all browsers                      // 除了area,br,col,embed,hr,img,input,link,meta,param这些标签外,                      // 将开始标签末尾加入斜杠的标签转换为开始和结束标签                      elem = elem.replace(rxhtmlTag, "<$1></$2>");                      // Go to html and back, then peel off extra wrappers                      // 获取左边第一个标签元素                      tag = ( rtagName.exec( elem ) || ["", ""] )[1].toLowerCase();                      // 获取最外层元素的包裹元素,并将元素包裹在其中                      wrap = wrapMap[ tag ] || wrapMap._default;                      depth = wrap[0];                      div.innerHTML = wrap[1] + elem + wrap[2];                      // Move to the right depth                      // 如果元素的包裹深度大于1,div重新赋值为元素最近的包裹元素(即:包含第一层包裹元素)                      while ( depth-- ) {                          div = div.lastChild;                      }                      // Remove IE's autoinserted <tbody> from table fragments                      // 在IE6,7中,清除字符串中空table标签中自动加入的tbody标签(手动加入的除外)                      if ( !jQuery.support.tbody ) {                          // String was a <table>, *may* have spurious(伪造的) <tbody>                          // 判断字符串中是否拥有空tbody标签                          hasBody = rtbody.test(elem);                          // 如果最外层标签为table且table中没有手动加入tbody                          // 变量tbody为div.firstChild.childNodes(自动加入的tbody标签集合)                          tbody = tag === "table" && !hasBody ?                              div.firstChild && div.firstChild.childNodes :                              // String was a bare <thead> or <tfoot>                              // 如果字符串中仅有一个空thead或tfoot标签                              // 变量tbody为div.childNodes(字符串中的thead和tfoot标签集合)                              wrap[1] === "<table>" && !hasBody ?                                  div.childNodes :                                  [];                          for ( j = tbody.length - 1; j >= 0 ; --j ) {                              // 排除thead或tfoot标签                              if ( jQuery.nodeName( tbody[ j ], "tbody" ) && !tbody[ j ].childNodes.length ) {                                  // 清除空table标签中自动加入的tbody                                  tbody[ j ].parentNode.removeChild( tbody[ j ] );                              }                          }                      }                      // IE completely kills leading whitespace when innerHTML is used                      // 在ie9以下浏览器中,字符串以空白字符串开头,将空白字符串作为div元素的第一个文本子节点                      if ( !jQuery.support.leadingWhitespace && rleadingWhitespace.test( elem ) ) {                          div.insertBefore( context.createTextNode( rleadingWhitespace.exec(elem)[0] ), div.firstChild );                      }                      // 获取已经处理完毕的div子节点集合(nodeList对象)                      elem = div.childNodes;                      // Take out of fragment container (we need a fresh div each time)                      // 在下一次循环处理字符串数组项前,清除处理创建过的div元素                      div.parentNode.removeChild( div );                  }              }              // 如果elem为DOM节点(文本节点)              if ( elem.nodeType ) {                  ret.push( elem );              }              // 将nodeList对象中节点合并到返回的数组中              else {                  jQuery.merge( ret, elem );              }          }          // Fix #11356: Clear elements from safeFragment          if ( div ) {              elem = div = safe = null;          }          // Reset defaultChecked for any radios and checkboxes          // about to be appended to the DOM in IE 6/7 (#8060)          // 在ie6,7中,拥有checked属性的单选按钮,复选框在插入到其他标签后,选中状态会失效(下面代码修复该bug)          if ( !jQuery.support.appendChecked ) {              for ( i = 0; (elem = ret[i]) != null; i++ ) {                  if ( jQuery.nodeName( elem, "input" ) ) {                      fixDefaultChecked( elem );                  } else if ( typeof elem.getElementsByTagName !== "undefined" ) {                      jQuery.grep( elem.getElementsByTagName("input"), fixDefaultChecked );                  }              }          }          // Append elements to a provided document fragment          // 将ret数组中的各DOM节点插入到提供的文档碎片中          // 提取dom节点中的script节点，并添加到ret数组中，位置为其原父元素索引位置后          if ( fragment ) {              // Special handling of each script element              handleScript = function( elem ) {                  // Check if we consider it executable                  // 如果elem元素不存在type属性或者type值为javascript或者为ecmascript                  if ( !elem.type || rscriptType.test( elem.type ) ) {                      // Detach the script and store it in the scripts array (if provided) or the fragment                      // Return truthy to indicate that it has been handled                      return scripts ?                          scripts.push( elem.parentNode ? elem.parentNode.removeChild( elem ) : elem ) :                          fragment.appendChild( elem );                  }              };              for ( i = 0; (elem = ret[i]) != null; i++ ) {                  // Check if we're done after handling an executable script                  if ( !( jQuery.nodeName( elem, "script" ) && handleScript( elem ) ) ) {                      // Append to fragment and handle embedded scripts                      // 将elem元素添加到文档碎片中并处理嵌入的脚本(script标签元素)                      fragment.appendChild( elem );                      if ( typeof elem.getElementsByTagName !== "undefined" ) {                          // handleScript alters the DOM, so use jQuery.merge to ensure snapshot iteration                          jsTags = jQuery.grep( jQuery.merge( [], elem.getElementsByTagName("script") ), handleScript );                          // Splice the scripts into ret after their former ancestor and advance our index beyond them                          // 将script标签添加到数组，位置为其原父元素索引位置后                          ret.splice.apply( ret, [i + 1, 0].concat( jsTags ) );                          i += jsTags.length;                      }                  }              }          }          return ret;      }  });