function parse_xml (xmlStr) {
  text = xmlStr;
  //使用replace去空格
  text = "
" + text.replace(/(<w+)(s.*?>)/g,function($0, name, props){
      return name + " " + props.replace(/s+(w+=)/g," $1");
  }).replace(/>s*?</g,">
<");
  //处理注释
  text = text.replace(/
/g,"
").replace(/<!--(.+?)-->/g,function($0, text){
      var ret = "<!--" + escape(text) + "-->";
      return ret;
  }).replace(/
/g,"
");
  //调整格式  以压栈方式递归调整缩进
  var rgx = /
(<(([^?]).+?)(?:s|s*?>|s*?(/)>)(?:.*?(?:(?:(/)>)|(?:<(/)2>)))?)/mg;
  var nodeStack = [];
  var output = text.replace(rgx,function($0,all,name,isBegin,isCloseFull1,isCloseFull2 ,isFull1,isFull2){
      var isClosed = (isCloseFull1 == "/") || (isCloseFull2 == "/" ) || (isFull1 == "/") || (isFull2 == "/");
      var prefix = "";
      if(isBegin == "!"){//!开头
          prefix = setPrefix(nodeStack.length);
      }else {
          if(isBegin != "/"){///开头
              prefix = setPrefix(nodeStack.length);
              if(!isClosed){//非关闭标签
                  nodeStack.push(name);
              }
          }else{
              nodeStack.pop();//弹栈
              prefix = setPrefix(nodeStack.length);
          }
      }
      var ret =  "
" + prefix + all;
      return ret;
  });
  var prefixSpace = -1;
  var outputText = output.substring(1);
  //还原注释内容
  outputText = outputText.replace(/
/g,"
").replace(/(s*)<!--(.+?)-->/g,function($0, prefix,  text){
      if(prefix.charAt(0) == "
")
          prefix = prefix.substring(1);
      text = unescape(text).replace(/
/g,"
");
      var ret = "
" + prefix + "<!--" + text.replace(/^s*/mg, prefix ) + "-->";
      return ret;
  });
  outputText= outputText.replace(/s+$/g,"").replace(/
/g,"
");
  return outputText;    
}


function setPrefix(prefixIndex) {
  var result = "";
  var span = "    ";//缩进长度
  var output = [];
  for(var i = 0 ; i < prefixIndex; ++i){
      output.push(span);
  }
  result = output.join("");
  return result;
}