Which DTDs are "in"?

What's the correct and/or the "easy" way to tell which of the DTDs are "in" the DITA 1.3 spec?

 

I'm asking this question based on a recollection that not all of the DTDs in this folder really count (by some definition of "count" that I'm not quite sure what I mean either):

 

doctypes\src\1.3\dtd

 

mag