Dead key

A dead key or key combination does not generate a character when struck, but modifies the character generated by the key struck immediately after. On some systems, there is no indication to the user that a dead key has been struck, but in some text-entry systems the diacritical mark is displayed along with an indication that the system is waiting for another keystroke: either the base character to be marked, an additional diacritical mark, or space to produce the diacritical mark in isolation.

Many languages use the Latin alphabet and have diacritically-marked letters for which unique keys do not exist on all keyboards. For example, on some keyboard layouts, the acute accent key is a dead key; in this case, striking acute accent then a results in á. Acute accent followed by space results in an acute accent in isolate form.

Most modern old keyboards conform to the ISO 9995 layout. This layout was first defined by the user group at AFNOR in 1984 working under the direction of Alain Souloumiac [1]. Based on this work, a well known ergonomic expert wrote a report (Yves Neuville, Le clavier bureautique et informatique, Cedic-Natan 1985) which was adopted at the ISO Berlin meeting in 1985 and became the reference for the keyboards’ layout.

In Mac OS X, many keyboard layouts employ dead keys. The U.S. Extended layout employs dead keys extensively (reached with option and option-shift) allowing a large inventory of characters to be easily typed. In the U.S. layout, the following smaller selection of dead keys appears (all reached with simply option):

  • option-e (á, é, í, ó, ú)
  • option-` (à, è, ì, ò, ù)
  • option-u (ä, ë, ï, ö, ü, ÿ)
  • option-i (â, ê, î, ô, û)
  • option-n (ã, õ, ñ)
  • option-c (ç)

The user simply types the base character after striking the dead key. For example, the key-strokes option-e and e result in the character é. In Mac OS X, pressing one of these key combinations creates the accent and highlights it, then the final character appears when the key for the base character is pressed. Some diacritically-marked Latin letters, of course, such as ŵ (used in Welsh), cannot be typed with the U.S. layout. That layout, which predates Unicode, provides access only to characters found in the legacy Mac Roman character set and does not support other diacritics, such as ˇ (caron), that are not commonly found in Western European languages (but which are commonly used in many Eastern European languages). However, the Mac OS X U.S. Extended keyboard layout, which was released after Unicode support became common, does provide access to many more diacritics.

The X Window System (used by most Unix-like operating systems, including most Linux distributions) support a Compose key. This dead key allows access to a wide range of extra characters by interpreting the next keystrokes following it. Some keyboards have a key labelled "Compose", but any key can be configured to serve this function.

In AmigaOS dead keys were called "deaf keys" and were generated by the pressing of ALT key (Eg: "ALT-F" combination of keys + "a" key results in "á"; "ALT-G" combine + "e" results in "è"; etc.). AmigaOS was the first Operating System to use officially an international approved standard ANSI ISO8859-1 layout for all its internal codepage operations and keyboard layout.

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Dead keys are commonly used to generate accented letters, because that way one does not need one key for each possible combination of letter and accent, but only one dead key for each accent in addition to the usual letter keys.

For example, if a keyboard has a dead key `, the French character e accent grave (è) can be generated by pressing first `, then e. Usually pressing a dead key followed by space produces the character denoted by the dead key; e.g. ¨space results in “¨”.

By construction, this has no restrictions on a typewriter, so you could place one on a q for example: With Unicode combining characters, this might look like q́. On the other hand, computers often do not work this way; ´q results in ´q.

In Microsoft Word, using the Control key with a key that usually resembles the diacritic (e.g. ^ for a circumflex) acts as a dead key. Many non-English keyboard layouts have dead keys directly on the keyboard. The US-International keyboard layout available on Windows and the X Window System place dead keys directly on similar-looking punctuation marks.

Old computer systems such as the MSX often had a special labeled “dead key”, which in combination with the Ctrl and Shift keys could add the accents ´, `, ˆ and ¨ to vowels that were typed subsequently.

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Some common compose combinations
' a á
' A Á
" a ä
" A Ä
` a à
` A À
~ a ã
~ A Ã
^ a â
^ A Â
o a å
o A Å
Vowels support most of the above
s s ß
, c ç
, C Ç
O R ®
O C ©
< < «
> >  »
. . ·
x x ×
-  : ÷
^ 0 °
^ 1 ¹
^ 2 ²
^ 3 ³
s o/0 §
1 2 ½
1 4 ¼
3 4 ¾
/ O ø
/ O Ø
- d ð
- D Ð
~ n ñ
t h þ
a e æ
 !  ! ¡
 ?  ? ¿
- L £
= E
= Y ¥
| c ¢
o x ¤
/ / \

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Posted by 구차니