Subject should be of the Content type (allowing the various mime type
declarations and and mode declarations).
Because their *are* so many ways to categorize things, and
categorization systems are rapidly changing, I don't think a hard
system is usefully specifiable -- build for the flexibility Adam
talks about =)
<subject>
Dogs in Space
</subject>
<subject mode="escaped">
Dogs in Space
</subject>
<subject mode="xml">
<pets>
<space>Dogs</space>
</pets>
</subject>
This means that a client will need to understand the scheme being
used by its upstream provider if it wants to make use of the
categorization -- which is FINE. Let separate standards for arbitrary
categorization emerge and let Atom worry about syndication rather
than reinventing another dewy decimal system.
-Brian