STY: # TODO, # FIXME, # XXX, others?
When looking for things that need attention, I usually grep for `# FIXME:` followed by `# TODO`.  But every so often I see a `# XXX: ` which will be missed by this heuristic.  This raises two questions:

1) Are there other common usages besides "XXX" that I'm not aware of?
2) Should we standardize on some usage patterns?

<b>Update</b> Also: comments with "?" but no TODO/FIXME label that might merit TODO