DOCBOOK: Marking Emacs keybindings

[Massimiliano Mirra <list@chromatic-harp.com>]

I am writing some documentation about Emacs, and the way keybindings
are traditionally represented (`C-f', `C-h C-f', `M-v'...) seems not
too prone to bend to DocBook mark up.  They will appear both in
<informalexample>'s and inline in paragraphs.  

I tried with <keycombo> and <keycap> tags but did not come up with
anything satisfying.  Any hint?  What could be a reasonable
<something>C-h C-f</something>, i.e. a tag enclosing it all?

Massimiliano