//为firefox的XMLDocument增加LoadXML,SelectNodes,SelectSingleNode方法的通用库

if(document.all)
{
    //do nothing
}
else
{
    XMLDocument.prototype.loadXML = function(xmlString)
    {
        var childNodes = this.childNodes;
        for (var i = childNodes.length - 1; i >= 0; i--)
            this.removeChild(childNodes[i]);

        var dp = new DOMParser();
        var newDOM = dp.parseFromString(xmlString, "text/xml");
        var newElt = this.importNode(newDOM.documentElement, true);
        this.appendChild(newElt);
    };

    // check for XPath implementation
    if( document.implementation.hasFeature("XPath", "3.0") )
    {
       // prototying the XMLDocument
       XMLDocument.prototype.selectNodes = function(cXPathString, xNode)
       {
          if( !xNode ) { xNode = this; } 
          var oNSResolver = this.createNSResolver(this.documentElement)
          var aItems = this.evaluate(cXPathString, xNode, oNSResolver, 
                       XPathResult.ORDERED_NODE_SNAPSHOT_TYPE, null)
          var aResult = [];
          for( var i = 0; i < aItems.snapshotLength; i++)
          {
             aResult[i] =  aItems.snapshotItem(i);
          }
          return aResult;
       }

       // prototying the Element
       Element.prototype.selectNodes = function(cXPathString)
       {
          if(this.ownerDocument.selectNodes)
          {
             return this.ownerDocument.selectNodes(cXPathString, this);
          }
          else
          {
              throw "For XML Elements Only";
          }
       }
    }

    // check for XPath implementation
    if( document.implementation.hasFeature("XPath", "3.0") )
    {
       // prototying the XMLDocument
       XMLDocument.prototype.selectSingleNode = function(cXPathString, xNode)
       {
          if( !xNode ) { xNode = this; } 
          var xItems = this.selectNodes(cXPathString, xNode);
          if( xItems.length > 0 )
          {
             return xItems[0];
          }
          else
          {
             return null;
          }
       }
       
       // prototying the Element
       Element.prototype.selectSingleNode = function(cXPathString)
       {    
          if(this.ownerDocument.selectSingleNode)
          {
             return this.ownerDocument.selectSingleNode(cXPathString, this);
          }
          else{throw "For XML Elements Only";}
       }
    }
}