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Version | 6.1 |
Authors | Mark Davis (mark.davis@us.ibm.com, home) |
Date | 2000-08-31 |
This Version | http://www.unicode.org/unicode/reports/tr19/tr19-6.1 |
Previous Version | http://www.unicode.org/unicode/reports/tr19/tr19-6.html |
Latest Version | http://www.unicode.org/unicode/reports/tr19 |
This document specifies a Unicode transformation format that provides serializes a Unicode codepoint as a sequence of four bytes. It provides a name that can be used to refer to the subset of ISO/IEC 10646 UCS-4 values that are available Unicode code points, from U+0000 to U+10FFFF.
This document has been reviewed by Unicode members and other interested parties, and has been approved by the Unicode Technical Committee as a Unicode Technical Report. It is a stable document and may be used as reference material or cited as a normative reference from another document.
A Unicode Technical Report (UTR) may contain either informative material or normative specifications, or both. Each UTR may specify a base version of the Unicode Standard. In that case, conformance to the UTR requires conformance to that version or higher.
A list of current Unicode Technical Reports is found on http://www.unicode.org/unicode/reports/.
For more information about versions of the Unicode Standard, see http://www.unicode.org/unicode/standard/versions/
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Please mail corrigenda and other comments to the author(s).
The preferred encoding form for Unicode text is the 16-bit form: UTF-16. There is also an 8-bit encoding form called UTF-8 that can be used to represent Unicode in environments where the 16-bit form is impractical due to compatibility constraints. In addition, some implementations may wish to use a 32-bit form, where each Unicode code point (aka scalar value) corresponds to a single 32-bit unit. Even those applications that do not use this form may want to convert to and from it for interoperability.
The following lists the important features of this encoding form:
ISO/IEC 10646 defines a 4-byte encoding form called UCS-4. Since UTF-32 is simply a subset of UCS-4 characters, it is conformant to ISO/IEC 10646 as well as to the Unicode Standard.
As of the recent publication of the second edition of ISO/IEC 10646-1, UCS-4 still assigns private use codepoints (E0000016..FFFFFF16 and 6000000016..7FFFFFFF16) that are not in the range of valid Unicode codepoints. To promote interoperability among the Unicode encoding forms JTC1/SC2/WG2 has approved a motion removing those private use assignments:
Resolution M38.6 (Restriction of encoding space) [adopted unanimously]
"WG2 accepts the proposal in document N2175 towards removing the provision for Private Use Groups and Planes beyond Plane 16 in ISO/IEC 10646, to ensure internal consistency in the standard between UCS-4, UTF-8 and UTF-16 encoding formats, and instructs its project editor [to] prepare suitable text for processing as a future Technical Corrigendum or an Amendment to 10646-1:2000."
While this resolution must still be turned into a Technical Corrigendum or an Amendment to 10646-1:2000, the Unicode Technical Committee has every expectation that once the text for that Technical Corrigendum or Amendment starts its formal balloting it will proceed smoothly to formal approval and publication as part of that standard.
Until the formal balloting is concluded, the term UTF-32 can be used to refer to the subset of UCS-4 characters that are in the range of valid Unicode code points. After it passes, UTF-32 will then simply be an alias for UCS-4 (with the extra requirement that Unicode semantics are observed).
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