[Serusers] presence xml format and SER

[Curro]

Hello all

I have a question about presence xml document in SER.
I would like to know whether this xml is based on any RFC or draft. 
I've been reading  Presence Information Data Format
<draft-ietf-impp-cpim-pidf-08.txt> and I have found nothing about <atom>
element. Should UA support this element?

Could you give some information? 

Thank you very much

Curro