[maemo-developers] rx-51 xkb file: how does FOUR_LEVEL type work?

[From: Denis DeLaRoca]

On Mon, 1 Feb 2010, Frantisek Dufka wrote:

> The trick is to press shift first, not Fn.
>
> Just tried with my N900 and mapped shift+Fn+Backspace to Escape and it works. 
> Also tried shift+Fn+qwertyuiop to F1-F10 and at least fullscreen and zoom 
> keys (F6,7,8) work.

Ok, I did your suggested remapping as follows,

partial alphanumeric_keys
xkb_symbols "us" {
     include "nokia_vndr/rx-51(english_base)"
     include "nokia_vndr/rx-51(arrows_4btns)"
     name[Group1] = "U.S. English";
     // 1. row
     key <AD01>	{ [ q,	Q,  1, F1 ] };
     key <AD02>	{ [ w,  W,  2, F2 ] };
     key <AD03>	{ [ e,	E,  3, F3 ] };
     key <AD04>	{ [ r,  R,  4, F4 ] };
     key <AD05>	{ [ t,	T,  5, F5 ] };
     key <AD06>	{ [ y,	Y,  6, F6 ] };
     key <AD07>	{ [ u,	U,  7, F7 ] };
     key <AD08>	{ [ i,  I,  8, F8 ] };
     key <AD09>	{ [ o,	O,  9, F9 ] };
     key <AD10>	{ [ p,	P,  0, F10 ] };
};

and indeed the F6 key mapping works and toggles fullscreen... but I can 
only trigger F6 by pressing Fn+Shift "simultaneously". The method of 
"locking" either Fn or Shift first, doesn't work for me.

I then tried replacing the F6 mapping with,

     key <AD06>	{ [ y,	Y,  6, bracketleft ] };

but no luck, it doesn't work... a colleague with a French-version N900 has 
an RX-51 mapping with some FOUR_LEVEL functional mappings. See the 'fr' 
map here, http://www.natisbad.org/N900/rx-51. And as Arkady reported 
earlier, his russian layout has a mostly functional EIGHT_LEVEL... but it 
looks as if the hildon-layer is doing special processing for this.

The <AC01>, <AB04>, etc., labels I think can be broken as 1st char for 
"alphanumeric", 2nd letter for the keyboard row from the bottom and the 
digits the column on the keyboard... with the special keys having their 
own names. What I don't understand is how different row keys are mixed on 
different foreign layouts.

--denis