Annotation isue: which processor handles annotations?

In "2. Conformance", it appears to be assumed that the RELAX NG processor 
handles annotations.  I believe that there are many other possibilities, and 
we have to begin with our requirements.  For example, default value insertion can 
be done by a front end, back end (if valiation of defaults is done in advance), or 
application programs.

Cheers,

Makoto