add isDescendantOf and isAncestorOf

[ap]

It would be handy to test if an element is a parent/child of another element. This is particularly useful when handling event bubbling to determine if an event has already been handled (this is the most reliable technique I have found to date that works in most modern browsers).

I expect it would look something like this:

jQuery('#blah').isAncestorOf(someElement) and jQuery('#blah').isDescendantOf(someElement)

Alternatively but less accurately it could be called isParentOf/isChildOf.

My existing JS implementation runs in logarithmic time and is as follows:

/ test if a is a descendant of b */ function isDescendantOf(a, b) {

return isAncestorOf(b, a);

}

/ test if a is an ancestor of b */ function isAncestorOf(a, b) {

test if a is in b's parent chain var o = b; while (o) {

if (o === a)

return true;

o = o.parentNode; }

return false;

}

Having this as part of jQuery would be convenient.

[dmethvin]

Related to #4101.

[dmethvin]

Also see this epic thread from jQuery-Dev:

 http://groups.google.com/group/jquery-dev/browse_frm/thread/ac5ca8eaa64fe9f1/8b3cfed47617cb5d

[rwaldron]

Bringing this back for review

[dmethvin]

 http://api.jquery.com/jQuery.contains/