asterisk users - May 2007 - SIP SendURL

recently added support (with bug) for SendURL for SIP channel causes 
problem with nokia phones, as I reported in
http://bugs.digium.com/view.php?id=9821
it was quickly resolved,
but because I can't find any RFC what it is doing/how to use it, I would 
like to ask here,
if someone using this feature, or do you know according to what RFC this 
was added, please let me know. thanks
PJ