Should the validator not provide a warning (at the very
least) when the HTTP content-type header for an Atom
feed is something other than application/atom+xml?
According to the spec (section 2): Atom documents are
[...] identified with the "application/atom+xml" media
I don't know if that's enough to justify an error, but
unless something is said about it, we're never going to
get one-click subscription working.