DOCBOOK: dbhier.mod vs. dbpool.mod

[Jens Emmerich <Jens.Emmerich@encorus.com>]

Hello,

is there some documentation/presentation/old discussion (beyond TDG)
explaining the modularization of the DocBook DTD? For instance, I
wondered why %refcomponent.mix; is defined in dbhier while
%component.mix; is in dbpool. Both have the same definition except for
the %local.*; part and are shared accross several content models.

Curious,

Jens