== The old-fashioned and modern ways to remap keys in X (some notes)

As I [[mentioned recently XBackspaceShift]], I've been remapping my
keyboard in X for [[a very long time DeleteBackspaceSplit]]. In all
of this time, I've been using the traditional and now old fashioned
way of doing this, namely _xmodmap_. Xmodmap is now a deprecated
mechanism, although it still works; these days you usually want to
be remapping keys with _setxkbmap_.

You might wonder why X has two different programs for this. As you
could guess, it's the [[usual ../sysadmin/XCutAndPasteHistory]]
[[reason XFontTypes]]; X added a new system for handling keyboard
remapping without removing the old one (because X never removes
anything). Xmodmap uses the old system, which I believe has been
in X since at least the start of X11, while setxkbmap uses the new
system, [[the X KeyBoard extension
https://en.wikipedia.org/wiki/X_keyboard_extension]].

(Well, 'new' is relative here. XKB apparently dates from 1996,
almost two decades ago. I was a little bit surprised to find
that out, since I hadn't heard of it myself until recently.
This is probably the hazard of having become set in my X ways
a very long time ago.)

I'm not the right person to write up a big evaluation of the two
mechanisms against each other, because up until recently I hadn't
looked into XKB and _setxkbmap_ at all (and even now I only know a
bit). So from my limited perspective, the big difference between
the two is that _xmodmap_ offers relatively simple and direct
low-level control for weird operations while _setxkbmap_ gives you
simple ways to do most of what you often want, provided that you
can work out the right arguments.

To show what I mean by this, here is more or less the _xmodmap_
magic needed to swap Backspace and Delete keys and to make CapsLock
act as a Control key:

.pn prewrap on
>  keysym BackSpace = Delete
>  keysym Delete = BackSpace
>  
>  remove Lock = Caps_Lock
>  keycode 0x42 = Control_L
>  add Control = Control_L

You put this in a file and then run '_xmodmap FILE_' and magic
happens.

By contrast, here is the _setxkbmap_ command needed to make CapsLock
act as a Control key and make the right Windows key act as Compose:

>  setxkbmap -option ctrl:nocaps -option compose:rwin

You will notice that I have not shown you how to swap Backspace and
Delete with _setxkbmap_. That's because that particular change is
not among the predefined changes that XKB supports and once you
venture outside of those predefined changes, things become rather
complicated.

(The predefined changes themselves are documented in the
_xkeyboard-config_ manpage. The files that define what these options
and so on mean are all found under _/usr/share/X11/xkb_; see for
example _/usr/share/X11/xkb/symbols/ctrl_. If you look at these
files, you'll see that XKB configuration is, well, intricate.)

Because _setxkbmap_ fits my needs right now ([[now that I'm not
swapping Delete and Backspace XBackspaceShift]]) and because it's
apparently the more approved-of way these days, I've switched from
_xmodmap_ to _setxkbmap_. I probably would not have changed over if
I was doing anything that _setxkbmap_ couldn't handle through its
existing options for _-options_; while more sophisticated things
are possible, they appear to be a lot of work.

The ArchLinux wiki has some nice references on [[Keyboard configuration
in Xorg
https://wiki.archlinux.org/index.php/Keyboard_configuration_in_Xorg]],
[[xmodmap https://wiki.archlinux.org/index.php/Xmodmap]], and [[the
X KeyBoard extension
https://wiki.archlinux.org/index.php/X_KeyBoard_extension]].
While I accumulated a bunch of additional links while I was looking
into _setxkbmap_, I'm not going to put any of them here because I
don't know enough to assess their quality and whether they're up to
date.