Unicode control characters: Difference between revisions

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The control code ranges 0x00–0x1F ("C0") and 0x7F originate from the 1967 edition of [[US-ASCII]]. The standard [[ISO/IEC 2022]] (ECMA-35) defines extension methods for ASCII, including a secondary "C1" range of 8-bit control codes from 0x80 to 0x9F, equivalent to 7-bit sequences of {{ctrl|ESC}} with the bytes 0x40 through 0x5F. Collectively, codes in these ranges are known as the [[C0 and C1 control codes]]. Although ISO/IEC 2022 allows for the existence of multiple control code sets specifying differing interpretations of these control codes, their most common interpretation is specified in [[ISO/IEC 6429]] (ECMA-48).

The [[ISO/IEC 8859]] series of encodings conforms to [[ISO/IEC 4873]] (ECMA-43) level 1, a subset of ISO/IEC 2022 designed for 8-bit character encodings, and therefore designatesreserves the range 0x80–0x9F for use byas anon-printing codes by C1 control code setsets such as ISO/IEC 6429.<ref>{{citation|mode=cs1 |quotation=This set of coded graphic characters may be regarded as a version of an 8-bit code according to ISO/IEC 2022 or ISO/IEC 4873 at level 1. […] The shaded positions in the code table correspond to bit combinations that do not represent graphic characters. Their use is outside the scope of ISO/IEC 8859; it is specified in other International Standards, for example ISO/IEC 6429. |url=http://www.open-std.org/JTC1/sc2/wg3/docs/n411.pdf |title=Final Text of DIS 8859-1, 8-bit single-byte coded graphic character sets—Part 1: Latin alphabet No.1 |author=ISO/IEC JTC 1/SC 2/WG 3 |author-link=ISO/IEC JTC 1/SC 2 |id=[[ISO]]/[[IEC]] [[International Organization for Standardization#Standardization process|FDIS]] 8859-1:1998; JTC1/SC2/N2988; WG3/N411 |date=1998-02-12}}</ref> Unicode inherits its [[Basic Latin (Unicode block)|first]] and [[Latin-1 Supplement (Unicode block)|second]] blocks (comprising U+0000 through U+00FF) from ASCII and [[ISO/IEC 8859-1]], thus incorporating the C0 and C1 control code ranges (U+0000&ndash;U+001F, U+007F&ndash;U+009F) as general category "Cc". It does not assign normative names to these control codes, though it does assign them normative aliases.<ref name="aliases" />

Category "Cc" control codes can serve a variety of purposes, not limited to format effectors: for example, the default ASCII C0 set includes six format effectors ({{ctrl|BS}}, {{ctrl|HT}}, {{ctrl|LF}}, {{ctrl|VT}}, {{ctrl|FF}} and {{ctrl|CR}}), ten transmission controls, four device controls, four information separators and eight other control codes.<ref name="ir001">{{citation|mode=cs1 |author=ISO/TC 97/SC 2 |author-link=ISO/IEC JTC 1/SC 2#History |title=The set of control characters of the ISO 646 |date=1975 |publisher=ITSCJ/[[Information Processing Society of Japan|IPSJ]] |id=ISO-IR-1 |url=https://www.itscj.ipsj.or.jp/iso-ir/001.pdf}}</ref> Most of these characters play no explicit role in Unicode text handling, and are used only by higher-level protocols such as those used by [[terminal emulator]]s. Certain characters are commonly used for formatting or [[sentinel value|sentinel]] purposes: