Editing Compose key (section)

==Compared to other input methods==
[[File:Keyboard layout Czech.svg|thumb|300px|[[Czech language|Czech]] QWERTZ keyboard layout. Characters achieved using AltGr are shown in blue, dead keys are shown in red]]
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. This allows the sequence to be more [[mnemonic]], so it is easier to remember, possible to guess at if unknown, and can support far greater numbers of characters.

The primary disadvantage is that compose sequences always require at least one more keystroke. Inconvenient placement of the compose key can also slow typing.

The most common method used to enter characters not printed on the keys is a [[modifier key]] such as [[AltGr]]. This method suffers from the limitation that AltGr adds just two more (shifted and unshifted) associations for each key. The additional characters made available are typically customized to the local market and thus meet the needs of most users, most of the time. The default UK/Ireland layout, for example, provides (via AltGr+aeiou) the letters á é í ó ú that are needed for [[Irish language|Irish Gaelic]] but consequently not the letters à è ì ò ù needed for [[Scottish Gaelic]].

A [[dead key]] treats the first character in any sequence as a modifier for the next key[s]: when pressed, the key appears to have no effect until the next key is pressed. (Most systems try to make the choice of dead key a logical part of the character selection; this makes sense for [[diacritic|accent marks]] and the concept is extended to other symbols). For example, the [[backtick|grave]] ("backtick") key ({{char|`}}) is often a dead key:  to achieve {{char|à}}, the sequence {{keypress|`|a}} is used. Compound sequences are possible: for example to add a [[two dots (diacritic)]], the {{keypress|"}} seems an obvious candidate but clearly this heavily used key cannot be repurposed as a dead key. The solution is to modify it using AltGr, thus {{keypress|AltGr|2}}{{nbsp}}{{keypress|a}} delivers {{char|ä}}.{{efn|{{keypress|AltGr|2}} rather than {{keypress|AltGr|"}} because 2 and " share the same key in the UK/Ireland layout and {{keypress|AltGr|shift|2}} is already assigned to {{char|½}} ({{frac|1|2}}).}} Other combinations are rather less obvious than their compose-key counterparts: for example compare {{keypress|Compose|,|s}} with {{keypress|AltGr|{{=}}}}{{nbsp}}{{keypress|s}} for {{char|ş}} (ChromeOS with UK extended mapping).

[[Alt code]]s or [[Unicode input#hexadecimal input|Unicode numerical input]] could almost be considered a compose key, but use unintuitive numbers, instead of mnemonics, as the selector.

Modern GUI character choosers often require a search function that is not much different than the compose sequences to locate a character quickly.