how to convert my this class in mootool

function SOAPClientParameters()
{
	var _pl = [];
	this.add = function(name, value) 
	{
		_pl[name] = value; 
		return this; 
	}

	this.toXml = function()
	{
		var xml = "";
	    for(var p in _pl)
	    {
		    if(typeof(_pl[p]) != "function")
		    xml += "<" + p + ">" + _pl[p].toString().replace(/&/g, "&").replace(/g, ">") + ";
	    }
		return xml;	
	}
}