For some thing or another, comments included in externally defined parameter entities are reported in unobvious locations...
Interesting. I went back and looked at the result document again, and it seems that this is also true in my case. The DOCTYPE element is being replaced, not with the entire DTD, but with comments that seem to be extracted from the DTD. (I'm not sure if they all come from parameter entities, as in Steven's case -- I don't have the DocBook DTD to hand -- but they are clearly coming from that set of files.)
Sixten
