How to have multipl 'level 3' modifier using xkb

Question

I'm trying to improve my keyboard layout using xkb and it worked great using the default 4 levels (or should I say 2 levels? I don't really know the terms..

And when I'm at opening a parenthesis, I found xkb very poorly documented (or I don't know how to search).. Some speak of levels, some of groups, some define levels as shift being the first, AltGr the second and others consider the base character being the first then increamenting each combination. I mean there are many inconsistencies..)

Anyway, here is the default 4 "combinations" with the key M in some keyboards:

// Pressing   <M> <Shift+M> <AltGr+M> <Shift+AltGr+M>
key <AB07> { [ m ,    M    ,    mu   ,      mu       ] }; // m M µ µ

Is it possible to add into the mix others modifiers?

For example with one extra modifier for example the R Ctrl I can have 6 combinations:

// Pressing   <M> <Shift+M> <AltGr+M> <AltGr+Shift+M> <RCtrl+M> <RCtrl+Shift+M>
key <AB07> { [ m ,    M    ,    mu   ,    mu         , comma  , semicolon] };// m M µ µ , ;

Or even 8 combinations with all the three modifiers..
And in fact it seems that there is already an 8 level mapping in some symbol files with the keyword EIGHT_LEVEL

However I'm not looking to get 42 combinations for one key..

Rather I just want to avoid awkward combination for my fingers and for that I prefer to still have only limited combinations with "direct access", like so:

// Pressing   <M> <Shift+M> <AltGr+M>  <RCtrl+M>  <RWin>+M
key <AB07> { [ m ,    M    ,  comma  , semicolon ,    µ   ] }; // m M , ; µ

I would also want to map other characters or even moves (arrows, home/end, page up/down) with other unused modifiers (capslock, numlock)

How can I do this ?

Thank you very much.

Answer 1

There you can use group to achieve the "two keystrokes" objective :

key <AB07> { 
type[group1]= "FOUR_LEVEL",
type[group2]= "TWO_LEVEL_BIS",
symbols[group1]= [ m ,    M    ,  comma  , NoSymbol],
symbols[group2]= [ semicolon ,    µ ] 
};

Now you must define the type TWO_LEVEL_BIS for using your desired modifiers.

It is worth to know than Mode_switch is a key that increment the actual group, so have a look to it's definition.