ISO_Level3_Shift vs Mode_switch (was: Howto handle modified keys)

[Edgar Toernig]

Daniel Stone wrote:
>
> On Fri, Oct 20, 2006 at 06:50:46PM +0200, Edgar Toernig wrote:
> > This reminds me of a problem recently discussed on the icewm
> > mailing list.  There was a request to support AltGr in icewm.
> > Usually, AltGr is mapped to Mode_switch and the patch was looking
> > for a key with that symbol.  But it seems that nowadays some
> > keymaps put the symbol ISO_Level3_Shift on that key.  There
> > was even one report where a key-press gives Mode_switch and
> > the corresponding key-release gives ISO_Level3_Shift[1].
> 
> Level3 Shift explicitly moves into ... well, level three.  Shift
> increments the current shift level by one, level 3 sets the base shift
> level to three, so level 3 + shift shifts up to four.  This is essential
> in European keymaps.

Hmm... but how is this different to regular Mode_switch?  If I look
at my German/English (xmodmap) keymap I have up to 4 symbols for each
key: normal, shifted, Mode_switched, shift-Mode_switched.  Looks like
4 levels and Mode_switch switches to the 3rd.  Afaik, that's how things
have been for a very long time and I see no problem with it.

> Mode_switch switches to another group, of which there are not very
> many.

I've no idea what the difference between a group and a level is, sorry[1].

>From my limited understanding it seems more sensible to have an XK_-
Group_switch for the "new" feature of switching groups (whatever that
is) and keep the longstanding behaviour of Mode_switch to change levels.
Moving the old behaviour to a new symbol and using the old symbol for
something new seems wrong.  (But maybe I simply have a too limited view
as I only know German and US keymappings.)

Anyway, there's still the oddity that a single key (AltGr) sometimes
gives different symbols when pressed (Mode_switch) and released (ISO_-
Level3_Shift).  Apparently, not only apps are confused on how the AltGr
key is called - even the xkb keymap authors can't agree on its mapping
giving such strange results *g*

Ciao, ET.


[1] Sorry for my lack of xkb knowledge but it seems I'm too dumb for
xkb so I always turn it off and use the old xmodmap.