Extending DB5

What is the best way to add DB5 RelaxNG extensions, such that end-users 
can use multiple of those in the same document ?

I'm specifically thinking of the new DB5 extensions that two GSoC 
students are working on (API models, Website, etc.).

I imagine those two would either "include" the core DB5 grammar, or 
refer to them via "external".
What does a user need to do to declare that his document uses one or 
more of these extensions ? Does he need to write his own (minimal) 
grammar, including all the extensions he wants to use ? Something else ?

Also, is there any particular convention we should follow, as far as the 
use of namespaces is concerned ? Anything else ?


Thanks,
         Stefan

-- 

       ...ich hab' noch einen Koffer in Berlin...