I'm looking for a single xpath expression in javascript which selects a node, and when it is not available it selects a different node. E.g.

I want to select the <new> node, but when the <new> is not available it should return <old>. (new can come before and after old)
in javascript I can do the following
tuple.selectSingleNode( "new | old" )
but this always returns the first node that matches, in example <old>