Choosing an extension for bitmap-only SFNTs

I need to pick an extension for the bitmap-only SFNT fonts[1].  While
these fonts use the same file format as TrueType and OpenType fonts,
they do not fullfill the requirements of any of the four (!) TrueType
specifications.  Apple calls them ``sfnt-wrapped bitmap fonts'',
pfaedit calls them ``bitmap-only TTF fonts'', and Microsoft do not
call them at all.  These fonts are refused by Windows XP.

Because users expect files with a ttf or otf extension to contain
scalable fonts, they need to have a different extension.  Such fonts
are used by Apple (who do not use file extensions), but not by
Microsoft (who do); hence, I believe I need to pick a new one.

I suggest they should have the extension ``.sfnt'', with ``.sfn''
being recognised for compatibility with 8+3 systems.

Opinions collected so far:

  - David Dawes doesn't have an opinion either way, but he'd like me to
    consult with this list first.

  - Egbert Eich would prefer ``.sfn'' to be the default, as he
    believes this will lessen his support load.  (He's probably right,
    but I dislike making MS-DOS the default.)

I'll probably submit code to handle the new extension these next days,
and would be glad to hear from you as soon as possible.

                                        Juliusz

[1] http://www.pps.jussieu.fr/~jch/software/xfree86-bitmap-fonts.html