content model of reltable for bookmap

["Grosso, Paul" <pgrosso@ptc.com>]

I just noticed that you cannot put the various bookmap 
specializations of topicref (chapter, preface, etc.) into 
a reltable.  This seems like a potential oversight.  

I would think that a common way to populate a reltable 
would be to copy elements from other parts of the map 
into the reltable, but the way things are setup now 
this isn't possible.

Does it make sense to add the bookmap specializations
to the content model of reltable for the bookmap doctype?

paul