Comment 33 for bug 1013881

I've analysed the use of nbsp(levelX) in all the keyboards defined in
/usr/share/X11/xkb

Keyboards defining nbsp on level 3:
./symbols/tr: include "nbsp(level3)"
./symbols/fi: include "nbsp(level3)"
./symbols/lt: include "nbsp(level3)"
./symbols/fr: include "nbsp(level3)" // "French (legacy,
alternative)"
./symbols/no: include "nbsp(level3n)"
./symbols/ca: include "nbsp(level3s)"

Keyboards defineinf nbsp on level4:
./symbols/fi: include "nbsp(level4)"
./symbols/fi: include "nbsp(level4)"
./symbols/fr: include "nbsp(level4nl)" // The only keyboard using
level4nl -- which I think is buggy.

What nbsp(levelX) exactly means:
  nbsp:level2 Non-breakable space character at second level
  nbsp:level3 Non-breakable space character at third level
  nbsp:level3s Non-breakable space character at third level,
nothing at fourth level
  nbsp:level3n Non-breakable space character at third level, thin
non-breakable space character at fourth level
  nbsp:level4 Non-breakable space character at fourth level
  nbsp:level4n Non-breakable space character at fourth level, thin
non-breakable space character at sixth level
  nbsp:level4nl Non-breakable space character at fourth level, thin
non-breakable space character at sixth level (via Ctrl+Shift) ---- Broken
with RhythmBox

We have the following choices after dropping the level4nl (which is the
cause of the RhythmBox problem):
– using level4n works (I've tested it), but actually I can't produce
thin-nbsp as I don't know how to get sixth level. However, fr-oss defines
thin-nbsp on AltGr-V.
– using level4 might work just like level4n (I can test it). It has the
advantage of being in use in finish keyboard (fewer risk of bug).
– level3s is in use in Canada, but as you said, some people have complained
that it leads to mistyping (I don't agree, but it is only my opinion).

If you want nbsp accessible from the space bar, with a slight change for
those who use AltGr-Shift-Space to get nbsp, choose level3n.
     * nsbp on AltGr-Space / thin-nbsp on AltGet-Shift-Space and AltGr-V)
If you want a conservative choice, choose level4 (thin-nbsp still available
on Alt-Gr V).
     * nsbp on AltGr-Shift-Space / thin-nbsp on AltGr-V)

I prefer the first option, but I won't complain if you choose the
conservative one.