In many languages there’s a need to add decorations, or glyphs to characters, like for example é or č. These are called diacritics¹. These characters don’t exist on a US Standard qwerty keyboard. There is the US International version with dead keys, which allow for crafting these special characters by pressing the desired diacritic key followed by the character to apply it to. So for example pressing ~ followed by n results in an ñ.

This is a great solution for most people, as it is intuitive and works well. There’s a downside you may have spotted, which is that when you actually want to use a tilde, a caret, an apostrophe, or any other special key linked to a diacritic, you’ll need to follow it with a space in order to generate the special character on its own. For anyone who writes code, this is a huge hassle. Suddenly, typing a single quotation mark requires two keystrokes (the apostrophe key followed by space). This may seem like a small gripe, but it adds up quickly.

Luckily, there’s a huge pointless button right on the home row that can be made to do something magical!

CapsLock as a compose key

The CapsLock key is—in my opinion—a waste of space. I never need to type anything in ALL CAPS, so locking the keyboard to uppercase is not a function I need. It’s also placed on prime real-estate, right where my fingers rest. Now there’s a special button that existed on keyboards of old, called the compose key². Pressing the compose key begins a key press sequence that involves (usually two) additional key presses, which will then yield a character composed of the two, so like the dead keys, but with a leader key. Modern keyboards do not have this key, fortunately you can map any key to function like it on Linux.

X11

So replacing the CapsLock key with the Compose key is an ideal solution for being able to use diacritics. This can be done in several ways. For example, on X11, you can add the command below to an autostart.sh script you run on boot. Or maybe in your ~/.profile or ~/.xinitrc. On desktop environments you can make the command below into a .desktop file. And window managers like i3 offer startup commands like exec --no-startup-id, which you can use to issue the command.

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setxkbmap -option compose:caps &

Wayland

On Wayland I personally use Hyprland as my window manager, or well compositor. Within it, the compose key can be set in the hyprland.conf file, like so:

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input {
    kb_options = compose:caps
}

It is also possible to set it using NixOs’s session variables, which I haven’t tried myself, as the Hyprland solution works fine for me. Anyway, in NixOS you could set something like:

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environment.sessionVariables = {
  XKB_DEFAULT_OPTIONS = "compose:caps";
};

Conclusion

Now I am able to add special characters without any fuss and there are loads of possible combinations to create special characters. Some of my favorites:

And more can be found on Dartmouth’s Department of Mathematics’s website³.