Compose key

A compose key, also called multi key, is a part of the computer keyboard that is—or behaves like—a kind of special dead key. Thus, unlike a modifier key, which must be held down, the compose key can be released before the following key stroke. The effect of the compose key is to convert to a dead key every specified key that is pressed after it. The next (or even a later) keypress triggers the insertion of an alternate character, typically a precomposed character or a symbol.

Being a dead key, the compose key only needs one key position. This is ideally in the Base shift state, while the other key positions may be attributed to other characters or dead keys. On the other hand, with respect to compact keyboards, the compose key may also be hidden in one of the present classic dead keys, for example ^Q. More generally, any dead key may be programmed to compose much more than what it is expected to produce, a principle that is already used for multiply diacriticized characters. Having one dedicated compose key on every keyboard, regardless of the number of other dead keys, proves however to be the most useful option.

For ergonomics, the preferred place for the Compose key is Right Alt, especially on keyboards that do not use Right Alt as AltGr. If they do, the user might eventually prefer to have Compose on Left Alt, which was already the place used first in history (an option that today should lead to place the lefthand Alt on Left ⊞ Win, and this on ≣ Menu, so that the reality-based prioritization of these keys would match the order of removal on compact keyboards, where an ≣ Menu key is often found but not Right ⊞ Win). Alternately, the Compose key may be placed on Right (or left) Ctrl.

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