XPath + Text Nodes

gistfile1.js

var getNodeTreeXPath = function(node){
	//	Built from Firebug source - 
	//	https://github.com/firebug/firebug/blob/235efff40332f85cb34b55f2da0de6bf98d083e4/extension/content/firebug/lib/xpath.js

	var paths = [], nodePath, element = node;

	//	If text node find its place among its siblings
	if(element.nodeType == Node.TEXT_NODE){
		var siblings = node.parentElement.childNodes;
		var nodeIndex = Array.prototype.indexOf.call(siblings, node)+1;

		nodePath = "node()["+nodeIndex+"]"; element = node.parentElement;
	}

	if(element.id){
		paths.push('*[@id="'+element.id+'"]');
	} else {
		//	Use nodeName (instead of localName) so namespace prefix is included (if any).
		for (; element && element.nodeType == Node.ELEMENT_NODE; element = element.parentNode){
			var index = 0;
			var hasFollowingSiblings = false;
			
			for (var sibling = element.previousSibling; sibling; sibling = sibling.previousSibling){
				//	Ignore document type declaration.
				if(sibling.nodeType == Node.DOCUMENT_TYPE_NODE) continue;
				if(sibling.nodeName == element.nodeName) ++index;
			}

			for (var sibling = element.nextSibling; sibling && !hasFollowingSiblings; sibling = sibling.nextSibling){
				if(sibling.nodeName == element.nodeName) hasFollowingSiblings = true;
			}
			
			var tagName = (element.prefix ? element.prefix + ":" : "") + element.localName;
			var pathIndex = (index || hasFollowingSiblings ? "[" + (index + 1) + "]" : "");
			paths.splice(0, 0, tagName + pathIndex);
		}
	}

	//	Append text node path if we have one
	if(nodePath) paths.push(nodePath);

	return paths.length ? "//" + paths.join("/") : null;
};

Combined version of Firebug's XPath functions getElementTreeXPath and getElementXPath with basic text node support.