Dead key
From Free net encyclopedia
A dead key is a key on a typewriter or a computer keyboard that produces no output when it is pressed, but modifies the output of the next key pressed after it.
Usage
Dead keys are commonly used to generate letters with accents (diacritics), because that way one does not need one key for each possible combination of letter and accent, but only one key for each accent (the dead key) plus the usual letter keys.
For example, if a keyboard has a dead key "´", the French character e accent aigu (é) can be generated by pressing first "´", then "e".
By construction, this has no restrictions on a typewriter, so you could accentuate an "f" for example.
In many text processing programs, dead keys are typed using the Ctrl key with the punctuation mark that looks most like the accent.
With the advent of Unicode character encoding it is possible to combine any available diacritical mark with any other character. The "combining diacritical marks" can be found in Unicode space U+0300 – U+036F (see http://www.decodeunicode.org/index.php?nodeId=70007&page=1&lang=1 for a list). For example, you can combine ̃ (U+0303 Combining Tilde) with p so you get p̃, whether this makes sense or not.
More exotically, you can combine ̐ (U+0310 Combining Candrabindu) with ∞ so you get ∞̐.
Old computer systems such as the MSX often had a special ‘dead key’, which in combination with the Ctrl and Shift keys could add the accents ´, `, ˆ and ¨ to vowels that were typed subsequently.