Correct sort of MIME type for other stuff?

["Bill Kearney" <wkearney99@hotmail.com>]

Hi all,

Since things are marching along nicely with using application/rss+xml, how about
a discussion on how to best use it for another format seen with some weblogs;
UserLand's .opml format?  A discussion with Dave Winer indicates he's been
favoring the using of "text/x-opml" for these files.  That sounds good to me but
I'm no MIME type expert.  What's the consensus on using stuff with "x-"
prefixing?  Can anyone chime in with some commentary on the whole rationale
behind using text/ vs application/ and the x- prefixes?

Oh and following along with things, the RSS feeds from Syndic8 now send the
"application/rss+xml" content-type out.  We'd like to do the same with the .opml
and the OCS stuff.

Thanks,
Bill Kearney