For examples explicitly defining the compose key, a diamond symbol (♢) will be used.

As a user of open-source operating systems, and someone temporarily using a machine with Windows on loan while I wait to fix the fan in my laptop I was missing the capability to use the compose feature which allows for creation of special symbols, including things like the section sign (§) and long dash (—) which are typically integral characters I use for Minecraft mods and general communication. For fans of Pocket Monsters, they can also just type Pokémon real easily by punching in P—o—k—♢—'—e—m—o—n.

Many more uses for the compose key, however and they all are built intuitively, using special symbols in the order you would typically type things. For instance, <—- would make ←, whereas -—> would make →. But also, |—^ would make ↑ and |—v (lower-case) would make ↓.

As an aside, I can't do up arrow or down arrow in open-source systems, likely I would have to edit my keymap bindings to allow it.

The magic I am using in Windows to make the compose key a reality in this instance which is proprietary is WinCompose.

All of the open-source staples I've shown above are possible, and many more with such things like em☺ji support, input by name (ex. ♢—♢—p—l—a—y— —b—u—t—t—o—n = ▶️) and extra functions which are harder or impossible to configure in open-source systems. You can download from GitHub either a desktop-installable instance or portable instance which will show up for anyone using the PortableApps platform to keep on a USB-connected media for use on other machines.