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A dead key is a special kind of a modifier key on a mechanical typewriter, or computer keyboard, that is typically used to attach a specific diacritic to a base letter.〔http://www.merriam-webster.com/dictionary/dead%20key〕 The dead key does not generate a (complete) character by itself, but modifies the character generated by the key struck immediately after. Thus, a dedicated key is not needed for each possible combination of a diacritic and a letter, but rather only one dead key for each diacritic is needed, in addition to the normal base letter keys. For example, if a keyboard has a dead key for the ''grave accent'' (`), the French character ''à'' can be generated by first pressing and then , whereas ''è'' can be generated by first pressing and then .〔The Unicode Standard, version 8.0.0, ch.05, §12 Strategies for Handling Nonspacing Marks: Keyboard Input | http://www.unicode.org/versions/Unicode8.0.0/ch05.pdf#G1076〕 Usually, the diacritic in an isolated form can be generated with the dead key followed by ''space'', so a plain grave accent can be typed by pressing and then . This legacy behavior is newly replaced with a more efficient one with respect to the use of combining diacritics following the Unicode Standard. The combining diacritic is then obtained with , while a spacing form of the diacritic is inserted with (typically + or +). ==Usage== A dead key is different from a typical modifier key (such as or ) in that, rather than being pressed and held while another key is struck, the dead key is ''pressed and released'' before striking the key to be modified. In some computer systems, there is no indication to the user that a dead key has been struck, so the key appears dead, but in some text-entry systems the diacritic is displayed along with an indication that the system is waiting for another keystroke to complete the typing sequence. On a typewriter, the character modifier functionality is accomplished mechanically by striking the diacritical mark without advancing the carriage (in modern terms, that diacritical mark keys are non-spacing). Thus, the following letter will strike the same spot on the paper. By construction, this has no restrictions on a typewriter, so one could place an acute accent ( ´) on a ''q'', for example.Computers do not, however, work this way. On a computer, the dead key temporarily changes the mapping of the keyboard for the next keystroke, so it activates a special keyboard mode rather than generates a modifier character. Instead of the normal letter, a precomposed variant of it with the appropriate diacritic is generated. Each combination of a diacritic and a base letter must be specified in the character set and supported by the font in use. As there is no precomposed character to combine the acute accent with the letter ''q'', striking and then is likely to result in ´q, with the accent and letter as separate characters, or in some systems the invalid typing sequence may be discarded. (Using the combining characters available in the Unicode character set, it may be possible to generate a combination that more or less looks like a ''q'' with an acute accent – q́ – but this is a technique quite distinct from the dead key functionality.) 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Dead key」の詳細全文を読む スポンサード リンク
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