Unicode input

character mapping tool shown displaying a subset of the Unicode Mathematical Operators|alt= Unicode input is a method to encode specific characters that are not directly available on a physical keyboard. Characters can be entered either by selecting them from a display, by typing a certain sequence or a 'chord' of keys on a physical keyboard, or by drawing the symbol by hand on touch-sensitive screen. In contrast to ASCII's 96 element character set (which it contains), Unicode encodes hundreds of thousands of graphemes (characters) from almost all of the world's written languages as well as many other signs and symbols. A comprehensive Unicode input system must provide for a large repertoire of characters, ideally all valid Unicode code points. This is different from a keyboard layout which defines keys and their combinations only for a limited number of characters appropriate for a certain locale. Nevertheless, the latter technique (particularly if an "extended" setting is used) is often adequate to satisfy the needs of most users, most of the time.

character mapping tool shown displaying a subset of the Unicode Mathematical Operators|alt=]] Unicode input is a method to encode specific characters that are not directly available on a physical keyboard. Characters can be entered either by selecting them from a display, by typing a certain sequence or a 'chord' of keys on a physical keyboard, or by drawing the symbol by hand on touch-sensitive screen. In contrast to ASCII's 96 element character set (which it contains), Unicode encodes hundreds of thousands of graphemes (characters) from almost all of the world's written languages as well as many other signs and symbols. A comprehensive Unicode input system must provide for a large repertoire of characters, ideally all valid Unicode code points. This is different from a keyboard layout which defines keys and their combinations only for a limited number of characters appropriate for a certain locale. Nevertheless, the latter technique (particularly if an "extended" setting is used) is often adequate to satisfy the needs of most users, most of the time. == Grapheme availability == An application can display a character only if it can access a computer font which contains a grapheme for that character. Fonts usually have incomplete Unicode coverage; most only contain the graphemes needed to support a few writing systems. However, most modern browsers and other text-processing applications are able to display multilingual content because they perform font substitution, automatically switching to a fallback font when necessary to display characters which are not supported in the current font. Which fonts are used for fallback and the thoroughness of Unicode coverage varies by software and operating system; some software will search for a suitable glyph in all of the installed fonts, others only search within certain fonts. ===.notdef=== If an application does not have access to a glyph for a required codepoint in the specified font (or in the system fallback font), the character should be shown as the glyph, 􏿮 . This often appears as an empty box, ☐ (nicknamed "tofu" based on the shape), a box with an X in it, ☒, a diamond with a question mark, �, or a box with a question mark in it, ⍰. ==Techniques== ===Extended keyboard mapping=== Most operating systems support an 'extended keyboard mapping' system setting, which is a facility to increase the repertoire of characters typically a precomposed character, a typographic symbol or punctuation mark, or other specialist graphemes beyond those enabled by the keyboard and keyboard mapping provided by default with the computer. The most well-known techniques include Alternate graphic ( or key) that gives a third and fourth meaning to every key; Compose key (sometimes called multi key), a key on a computer keyboard that indicates that the following (usually 2 or more) keystrokes trigger the insertion of an alternate character; A dead key, a normal key that is repurposed to affect the behaviour of the next key pressed. It is typically used to attach a specific diacritic to a base letter; or indeed combinations of these. The precise methods depend on which type of type of physical keyboard and (especially) the mapping used with it. === Decimal input (Alt codes) === Some programs running in Microsoft Windows, including recent versions of Word and Notepad, can produce characters from their Unicode code points expressed in decimal and entered on the numeric keypad with the key held down. For example, the Euro sign has 20AC as its hexadecimal code point, which is 8364 in decimal, so will produce the symbol. Decimal code points in the range 160 –255 must be entered with a leading zero (so that the Windows code page is chosen) and furthermore the Windows code page CP1252 must be used. For example, yields a , corresponding to its code point, but the character produced by depends on the , such as Code page 437, and may yield a  . Also through yield the characters assigned in rows 8 and 9 in the CP1252 layout, rather than the C1 control codes that are assigned to those numbers in Unicode. In programs which were not designed to handle Alt codes over 255, the character retrieved usually corresponds to the remainder when the number is divided by 256. The text editor Vim allows characters to be specified by two-character mnemonics referred to as digraphs. The installed set can be augmented by custom mnemonics defined for arbitrary code points, specified in decimal. For example, as decimal 9881 is equal to hexadecimal 2699, associates "Gr" with . See below for use of decimal code points in HTML. s representing the letter in various typefaces and as single- and double-storey; they are allographs of the same grapheme|class=skin-invert-image]] ==Notes==

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