XKB: purpose of virtualMods=... in symbols files

[Maxim Levitsky]

On Fri, 2009-08-28 at 17:46 +0300, Maxim Levitsky wrote:
> I currently am trying to understand how XKB works.
> 
> I pretty much understand most of it, descriptions on 
> http://www.unix.bat.ru/mirrors/pascal/en/xkb/
> 
> and the wonderful.
> 
> Ability to retrieve current xkb configuration using xkbcomp makes it
> even easier.
> 
> 
> I don't understand the purpose of virtualMods= in symbol files.
> 
> I was able to make use of this statement, but only like that:
> 	virtualMods=Vmod,
>         actions= [SetMods(modifiers=Vmod)]
> 
> 
> As this allows to set a virtual modifier from a symbol declaration.
> (but this feature isn't used at all)
> 
> However, standalone virtualMods= doesn't do anything, so why it is
> present in many symbol files, like:
> 
> // Both Ctrls pressed together toggle group
> partial modifier_keys
> xkb_symbols "ctrls_toggle" {
>   virtual_modifiers LControl, RControl;
>     key <LCTL> {
> 	type[Group1]="PC_RCONTROL_LEVEL2",
> 	symbols[Group1]= [ NoSymbol,	ISO_Prev_Group ],
> 	virtualMods= LControl
>     };
>     key <RCTL> {
> 	type[Group1]="PC_LCONTROL_LEVEL2",
> 	symbols[Group1]= [ NoSymbol,	ISO_Next_Group ],
> 	virtualMods= RControl
>     };
> };
> 

Any idea?

Best regards,
	Maxim Levitsky