OT: Push, CDF and early XML applications

Whenever I read about "push" technology, Microsoft's Channel Definition
Format (CDF) comes up. Apart from the xmlspec.dtd, I know no earlier XML
application (but hope someone will enlighten me), and I remember all XML
books at the time around the release of IE4 had a section on CDF, because
there was hardly any other known real-life examples.

My question is: what is the requirement for something to be called "push"?
Even in the case of channels, I assume the client has to emit a little
message to the server at certain intervals, saying that it's ready for new
data. Are there other known XML applications today that is push but not
labeled as such? Is RSS push?

Gustaf