I just got around to checking the spec, and it's pretty clear. Section 4.3.2
makes it clear that an external PE can begin with an <?xml text declaration;
I can't imagine that we'd allow that and forbid it in the external
subset but I can't see where we allow it explicitly ... so I suspect that
we're going to have to fix production 31 before we are finished. Thanks
to Mr. Anderson for this. -Tim