I'm sorry for the little OT of this post, but I think the question is not "Can I put binary data into an XML file?" but "Would I post binary data into an XML file?"
I mean, what is the reason for putting binary data into an XML file?
What are the advantages of doing this?
I think it is not the best way to handle binary data.
Anyways, this is a full decision of the developer, and the question was answered.

Sorry for the OT, again.

Cheers.