What purpose do sizcache and sizset serve in jQuery

Question

I am using jQuery, and in inspecting the DOM of my page in IE with the Dev Toolbar I see that many elements have sizset and sizcache attributes add

Answer 1

http://groups.google.com/group/jquery-en/browse_thread/thread/2382a66a1ce9edf6/168046b517318240?lnk=gst&q=nodeIndex#168046b517318240

it's meant for internal use only. The jQuery core file uses it to
calculate nth-child. Here is the source (with my emphasis):

It looks like nodeIndex and sizcache and sizset are all used internally to calculate the nth-child.