the bare symbol "-" was not being proposed as a separator al by itself.
actually, a big problem with the "-xml" suffix proposal is that it
assumes that there will never be any other content-type frobs used
in combination with "-xml". but enough things like this have been
proposed over the past 10 years that it seems likely that there will
be more such frobs. so I'd like to see a unique separator character
as opposed to one which already appears in several content-types.
I really don't want to restart this debate, however, I have to note that
there is substantial disagreement with your assessment that "enough things
like this have been proposed over the past 10 years...".
But regardless, I think avoiding separators we already use is a good idea. I
personally like "+", but I could live with any of the others as well.
Ned