[selectors4] Upwards Ancestor Traversal API

For event bubbling, it is very useful to traverse up the DOM tree to
find an ancestor. For example:

 findAncestorWithClass(el, className,  /*opt*/ container);
 findAncestorWithAttribute(el, attName, /*opt*/ value);
 jqueryObj.closest(selectorText, /*opt*/ context)

It would be useful to have an API that traverses up the DOM tree and
tests each Element against a selector and returns either an Element or
null.

Proposal:

 querySelectorAncestor(startNode, selectorText[, optional Node container);

If container is not specified, container is the root node.

Let currentParent be startNode.parentNode. While currentParent is not
container, if currentParent matches selectorText, it is returned.
-- 
Garrett
@xkit
ChordCycles.com
garretts.github.io