entities and characters?

I'm dealing with a DTD that uses character entities to represent 
typographic specs for bibliographies.  I know the schema languages 
don't do entities, so how would one deal with this in relax ng?  Use 
unicode numbers?  The characters themselves?

Put differently, is it a bad idea to develop a new DTD that relies on 
entities in this way, given the general shift away from DTDs in the XML 
world?  This is intended to be an xml equivalent to bibtex style files, 
so if successful, a couple/few years from now there should be a lot of 
them available.  Future proof-ness should be a goal, then.

Here's a fragment of an instance based on the DTD:

       <title beforesep="&lsquo;" aftersep="&rsquo;&period;"></title>
       <book>
	<prefix beforesep="&space;" aftersep="&space;">In</prefix>
	<editor aftersep=", ">
	  <name>
	    <surname weight="bold"></surname>
	    <forename beforesep="&comma;&space;"></forename>
	  </name>
	  <name beforesep=", " aftersep=",">
	    <surname></surname>
	    <forename beforesep="&comma;&space;"></forename>
	  </name>

Bruce