Very good point. There's no need for it at all UNLESS we clarify the
use of the charset parameter. For example, if you have
Content-type: text/richtext; charset=iso-8859-2
then the "us-ascii" formatting command makes a certain amount of sense.
I may be missing something about richtext, but it seems to me that as long
as you can have character sets other than US-ASCII, there is a need to be
able to switch back to the default character set from within a region that's
marked as being in something else. I use nested constructs of this sort all
the time in SGML variant I happen to have available. Indeed, I'm no SGML
expert, but if for some reason we have forbidden nesting of SGML regions
I think we've made a big mistake. If you cannot nest things you then need to
have the cartesian product of all the things you can set as individual
commands. That's a lot of commands...