Is NodeIndex A Valid DOM Element Property In IE?

I came across some javascript at work today that used jQuery to fetch two elements. It then used elem.nodeIndex to determine the position in the elements parent for each element. N

Solution 1:

It looks like it's jQuery that's adding nodeIndex to nodes in some cases.

Solution 2:

Well, the easy answer is: If it isn't documentated anywhere like MDC, MSDN or W3, then it isn't a 'real' DOM property.

The idea of using nodeIndex, is also wrong, why would you want to do that?