It turns out that, while my new and different Atom feed is somewhat more standards compliant, it still doesn't validate. The XML::Atom perl module I am using makes things easy, but doesn't give me enough hooks to make sure I'm generating all the structure I want to -- I can set some things semi-manually using "set" functions, but for some objects, there is not a way to do that. This is frustrating -- I may need to nudge the author (or find another module).
It is, however, very handy to know Perl, both for class stuff and for other things. Hurrah.