Technical descriptions, samples or examples

["Sjoerd van Egmond" <SjoerdvanEgmond@gmail.com>]

Dear all,

the company I'm working for (an enabler for selling printed photobooks) is
planning to change their payment-process. I've been looking into several
standard xml-formats and and decided that UBL, or maybe NES-UBL, is the
right format for us. Also because it enables us to change more of our
process to one and the same format.
My problem is that I can't seem to find any technical descriptions of the
format. I've found quite a lot of higher-level descriptions, but those
aren't enough to really implement it. Since I read UBL is widely accepted
I'm frustrated I can't find anything about UBL, while for cXML I've found it
instantly. Can you please direct me to an online reference with which I have
enough information to show my superiors this really is the language we have
to use.

thank you in advance,

-- 

Sjoerd van Egmond