Compose key

The Compose Character key[2][3] was introduced by engineers at Digital Equipment Corporation (DEC) on the LK201 keyboard, available since 1983 with the VT220 terminal.

Earlier versions of compose sequences followed handwriting and the overstrike technique by putting the letter first and diacritics second.

There is no intrinsic limit on sequence length, which should respect both the rules of mnemonics and ergonomics, and feasibility within a comprehensive compose tree.

The primary advantage of a compose key is that the sequence used to select the character can be made up of any letters, numbers, or symbols available on the keyboard.

The additional characters made available are typically customized to the local market and thus meet the needs of most users, most of the time.

[a] Other combinations are rather less obvious than their compose-key counterparts: for example compare Compose+,+s with AltGr+= s for ş (ChromeOS with UK extended mapping).

Alt codes or Unicode numerical input could almost be considered a compose key, but use unintuitive numbers, instead of mnemonics, as the selector.

[citation needed] To emulate the compose key for all software, keyboard shortcut utilities are often involved.

Such keyboard layouts can also be programmed directly in C (the language Windows drivers are written in), compiled using the free-of-charge Windows Driver Kit,[19] and packaged using the free-of-charge Microsoft Keyboard Layout Creator 1.4,[20] compatible up to the latest versions of the OS.

Although the Cocoa text input system allows entry of many alternate and accented characters natively in macOS,[21] a true compose-key solution is not built in.

[21] Although ChromeOS is supplied with a larger repertoire of glyphs than most competitors, the chords needed to achieve them are not always as obvious as the Compose concept provides.

[22][23] Under DOS, compose key support depended on the running application, or on a loadable keyboard driver.