javascript : convert a string to XML DOM

gistfile1.js

//this function convert the string representation of some XML
//into a DOM object.
function StringToXMLDom(string){
	var xmlDoc=null;
	if (window.DOMParser)
	{
		parser=new DOMParser();
		xmlDoc=parser.parseFromString(string,"text/xml");
	}
	else // Internet Explorer
	{
		xmlDoc=new ActiveXObject("Microsoft.XMLDOM");
		xmlDoc.async="false";
		xmlDoc.loadXML(string);
	}
	return xmlDoc;
}

gistfile2.js

// EXEMPLE FILE

//Ce bout de code retourne l'attribut url du premier tag image trouvé. 
var xmlDom=StringToXMLDom(xmlString);
if (xmlDom){
	var tmp=xmlDom.getElementsByTagName("image")[0];
	if (tmp!=undefined){
		var src=tmp.getAttribute("url");
		if (src) return src;
	}		
}

how to use it,man ?

in a code outside windows... where does window come from?
window.DOMParser