// $XA
//
// $XA(exp, context, resolver).forEach(function(node){});
function $XA (exp, context, resolver) {
	context || (context = document);
	var XPE = new XPathEvaluator();
	var Doc = context.ownerDocument || context, expr = XPE.createExpression(exp, resolver ? resolver :
		Doc.documentElement.namespaceURI ? function(prefix) {
			return XPE.createNSResolver(Doc.documentElement).lookupNamespaceURI(prefix) ||
			context.namespaceURI || document.documentElement.namespaceURI || "";
	} : null);
	var result = expr.evaluate(context, XPathResult.ANY_TYPE, null);
	switch (result.resultType) {
	case XPathResult.STRING_TYPE : return result.stringValue;
	case XPathResult.NUMBER_TYPE : return result.numberValue;
	case XPathResult.BOOLEAN_TYPE: return result.booleanValue;
	case XPathResult.UNORDERED_NODE_ITERATOR_TYPE:
		result = expr.evaluate(context, XPathResult.ORDERED_NODE_SNAPSHOT_TYPE, result);
		var length = result.snapshotLength;
		return {
			toA:function(){
				for (var i = 0, len = length, res = new Array(len); i < len; ++i)
					res[i] = result.snapshotItem(i);
				return res;
			},
			forEach:function(func, thisObject){
				for (var i = 0, len = length; i < len; ++i)
					func.call(thisObject,result.snapshotItem(i), i);
			},
			map:function(func, thisObject){
				for (var i = 0, len = length, res = []; i < len; ++i)
					res.push(func.call(thisObject,result.snapshotItem(i)));
				return res;
			},
			filter:function(func, thisObject){
				for (var i = 0, len = length, res = [], node; i < len; ++i)
					if (func.call(thisObject,node = result.snapshotItem(i))) res.push(node);
				return res;
			},
			mapfilter:function(func, thisObject){
				for (var i = 0, len = length, res = [], node; i < len; ++i)
					if (node = func.call(thisObject,result.snapshotItem(i))) res.push(node);
				return res;
			}
		};
	}
	return null;
}