customisation of docbook

Hi,

I want to define a w3c xml schema (rather than DTD) that includes or is 
a customisation of Docbook.  I have referenced oasis-open.org and found 
schema definitions that are equivalent to DTD.  The schema's do not 
appear to be as easily customisable as the DTD's.
With DTD, removing an element is accomplished by redefining the class 
and changing the entity module definition to IGNORE.  I don't see how to 
achieve this with the schema's.  Schema's appear to use substitution 
group as the mechanism for inclusion in a 'class'.  Elements definitions 
are used to define association to substitution group.  I don't see how 
to change these 'associations' to substitution group.  'redefine' and 
'restriction/extension' work on complex types, not elements.

Is DocBook v5 & RELAX NG the only answer, or am I missing something with 
the W3C schema's?

Thanks
Scott