5th value in xmodmap

[wettstae at gmail.com]

> I haven't found why my keyboard produces keycode 92 for AltGr, though the layout
> uses "<RALT> = 108;" so it should produce 108.

Maybe you looked at the xev output line 'XKeysymToKeycode returns
keycode'?  If multiple keys produce the same keysym (as here, RALT and
LVL3 both produce ISO_Level3_Shift), the keysym to keycode conversion is not
well defined.

> After all I would say that the xkb configuration is too complex and
> bad documented, but understandable in the end.

There are few useful resources online.  The best one I am aware of is
Ivan Pascal's pages:

  http://pascal.tsu.ru/en/xkb/

Somewhat useful is the 'The X Keyboard Extension: Protocol
Specification'.  It does not talk about syntax, but it is the most
definitive reference of XKB mechanisms.  For example, Section
12.2.2 might shed some light on how to understand the output of xmodmap.

> I would recommend to forget about xmodmap and use xkbcomp(1) and
> setxkbmap(1) to temporarily modify the produced symbols. You can
> define more than FOUR_LEVEL symbols. I found definitions with up to
> EIGHT_LEVEL types. Can you define even more?

You can define more.  Theoretically, 256 levels should be possible (as
there are eight real modifiers).  The layout I am using has 11 levels.
Already here, one starts hitting bugs: xkbcomp does not recognise
'Level9', 'Level10' and 'Level11', one has to write '9', '10' and '11'
instead.

> Another left-over question is: Is there a default or configured "system directory" to overwrite
> the "installation directory" settings in "/usr/share/X11/xkb", such as "/etc/X11/xkb"?

There is a bug for this:

  https://bugs.freedesktop.org/show_bug.cgi?id=74422

According to the 'Status' field, it is still open.

Andreas