DOCBOOK: XMLSpy and entities

Forgive this newbie if this has been answered elsewhere (or if 
this question should go to docbook-apps), but how do you get XML Spy to 
validate/accept external entities?

 

Specifically, I am creating a <book> that contains 
chapters that are created as separate xml files.

 

The entities are declared within the DOCTYPE 
declaration.

 

My markup looks almost exactly like the example in the online 
Definitive Guide and validates fine in XMetaL.

 

However, I would like to be able to use XMLSpy to take 
advantage of some of its XSL editing capabilities.

 

This list and other resources have been a great help in my 
learning XML.

 

Thanks.

 

Joe