> When we don't have any html-mode buffer at hand, that's obviously the
> better choice, yes.  When we do have html-mode buffers around, both
> choices make sense, depending on the situation.  Maybe it's better not
> to try to be clever about it, I don't know.

I think it's better not to be clever about it; I think having tags
disappear from the completion list because you have few HTML buffers
open will hurt more than presenting a too long completion list.

However maybe it would make sense to extend the completion list when
tags that aren't in `html-tag-alist' are used in a HTML buffer?

> Completion of user-chosen classes is a different matter, it would be
> great, and I've seen people asking for it a few times.

I've played around with this a bit and have got a basic version
working, see the attached patch. If it looks like something I can
chisel it onto a proper patch.

-- Simen