xkb vs ibus

[Geoff Streeter <geoff dyalog com>]

I maintain the apl keyboard for xkb.

There are things that make its usage different from "normal" layout switching.

1. For most language switching the switch is made for a word or a sentence. 
For apl the switch is normally made for a single character. If you think about 
maths the same would be true for a lot of mathematical character support.

2. xkb provides latching (while pressed) group shifts. Combining this with an 
apl layout means that the apl characters are available from any base language.

I have been struggling for some time to get this to work with recent Gnome.

Back in 2007 I supported the apl keyboard by deliberately defining all of 
characters in Group2 and placing special rules in the rules file to load them. 
At that time Sergey Udaltsov was developing his approach of making each 
language layout an xkb group. When this was adopted universally I switched to 
defining the characters in group1 and apl users just made apl their 2nd 
language layout so that the group switching would work well for them.

Now for some specifics (I am using a fresh Fedora 20):

1. I cannot seem to get the apl keyboard at all from the "input-sources" 
dialogue. It is in the "extras" part of the xkb/rules. I have done:
        gsettings set org.gnome.libgnomekbd.desktop load-extra-items true
but it does not seem to make difference.

2. If I do a setxkbmap -query from a terminal window it reports layouts as 
"gb,us". My base language is "gb" but I am at a loss as to where that "us" 
comes from.

3. Using dconf-editor and changing values in org|gnome|libgnomekbd|keyboard 
seems to have no effect.

Now I need to think about how to proceed. 

Will the input sources ever be switchable with a latching (while pressed) 
shift?

Will ibus-xkb continue to load layouts into xkb groups 1 to 4?

Is there a place where I can get apl into the layout list? So I would see 
(gb,apl) or possibly (gb,apl,us) if there is a reason to add the "us".

Geoff Streeter