Just as the title says. One way to make sure the "Until" methods accept more then just selectors is to use the filter method instead of jQuery().is from line 4556 from:

while ( cur && cur.nodeType !== 9 && ( until === undefined || cur.nodeType !== 1 || !jQuery( cur ).is( until )) ) {

To:

while ( cur && cur.nodeType !== 9 && ( until === undefined || cur.nodeType !== 1 || !jQuery( cur ).filter(until)[0] )) {

Now, correct me if I'm wrong here. But assuming you are comparing two DOM nodes to each other. Wouldn't it be a lot faster to compare those right away, so a new jQuery instance won't be created on each iteration? This way you would get something like:

while ( cur && cur.nodeType !== 9 && ( until === undefined || cur.nodeType !== 1 || !( cur === until || jQuery( cur ).filter( until )[0])) ) {

Heck, we could even use matchesSelector between them with something like this:

!( cur === until || ( typeof until === "string" && jQuery.find.matchesSelector( cur, until ) ) || jQuery( cur ).filter( until )[0])

Any thoughts?