[PATCH libX11] Add double-arrow compose sequence

[Geoff Streeter]

> 
> > Signed-off-by: Gabriel Souza Franco <gabrielfrancosouza at gmail.com>
> > ---
> >   nls/en_US.UTF-8/Compose.pre | 1 +
> >   1 file changed, 1 insertion(+)
> >
> > diff --git a/nls/en_US.UTF-8/Compose.pre b/nls/en_US.UTF-8/Compose.pre
> > index 23829b4..4a96570 100644
> > --- a/nls/en_US.UTF-8/Compose.pre
> > +++ b/nls/en_US.UTF-8/Compose.pre
> > @@ -4535,6 +4535,7 @@ XCOMM Part 3
> >   <Multi_key> <KP_Divide> <U2194> 	: "?"   U21AE # LEFT RIGHT ARROW WITH 
STROKE
> >   <Multi_key> <less> <minus> 	: "?" U2190 # LEFTWARDS ARROW
> >   <Multi_key> <minus> <greater> 	: "?" U2192 # RIGHTWARDS ARROW
> > + <Multi_key> <equal> <greater> 	: "?" U21D2 # RIGHTWARDS DOUBLE ARROW
> >   <Multi_key> <U2203> <U0338> 	: "?"   U2204 # THERE DOES NOT EXIST
> >   <Multi_key> <braceleft> <braceright>	: "?"   U2205 # EMPTY SET
> >   <Multi_key> <U2208> <U0338> 	: "?"   U2209 # NOT AN ELEMENT OF
> 
> Hmm, it's unfortunate that <less> <equal> is already mapped to
> 	"?" U2264 # LESS-THAN OR EQUAL TO
> so we can't have it match for the leftwards double arrow, but I'm
> not seeing any obvious better suggestions for the mapping, unless
> we want to do something like <minus> <minus> <greater> and
> <less> <minus> <minus>, but that seems klunkier.
> 
> Anyone else have thoughts or ideas?
> 
> 
I like these sequences to be visually coherent. So I am dubious of   
<Multi_key> <braceleft> <braceright>	: "?"   U2205 # EMPTY SET
I am fortunate in always working with an APL keyboard in the second xkb group 
so I would have opted for
<Multi key><U25CB><slash>
However, most people do not have the luxury of an APL keyboard so something 
else is required. I would suggest:
<Multi key><0><slash>

For the arrows I would want to tackle a whole group in a consistent manner. It 
might seem a bit left field but how about thinking of the numeric keypad to 
give direction and then we could use
<Multi key> <equal> <7> : " ⇖" U21FF LEFT RIGHT OPEN-HEADED ARROW
All of the DOUBLE ARROWs and OPEN-HEADED arrows would follow naturally from 
there.
The single arrows could equally follow using a <minus> as introducer.

Taking the line drawing characters and composing them with single arrows (I 
have those on APL keyboard) would give U21B0 UPWARDS ARROW WITH TIP LEFTWARDS 
and similar.

I am beginning to think that something more radical is required. The ability 
to compose characters that are themselves the result of compositions. Too 
ambitious? It would give us a route to be able to generate things like U21C5 
UPWARDS ARROW LEFTWARDS OF DOWNWARDS ARROW.