7Network Working Group F. Yergeau
8Request for Comments: 3629 Alis Technologies
11Category: Standards Track
14 UTF-8, a transformation format of ISO 10646
18 This document specifies an Internet standards track protocol for the
19 Internet community, and requests discussion and suggestions for
20 improvements. Please refer to the current edition of the "Internet
21 Official Protocol Standards" (STD 1) for the standardization state
22 and status of this protocol. Distribution of this memo is unlimited.
26 Copyright (C) The Internet Society (2003). All Rights Reserved.
30 ISO/IEC 10646-1 defines a large character set called the Universal
31 Character Set (UCS) which encompasses most of the world's writing
32 systems. The originally proposed encodings of the UCS, however, were
33 not compatible with many current applications and protocols, and this
34 has led to the development of UTF-8, the object of this memo. UTF-8
35 has the characteristic of preserving the full US-ASCII range,
36 providing compatibility with file systems, parsers and other software
37 that rely on US-ASCII values but are transparent to other values.
38 This memo obsoletes and replaces RFC 2279.
42 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
43 2. Notational conventions . . . . . . . . . . . . . . . . . . . . 3
44 3. UTF-8 definition . . . . . . . . . . . . . . . . . . . . . . . 4
45 4. Syntax of UTF-8 Byte Sequences . . . . . . . . . . . . . . . . 5
46 5. Versions of the standards . . . . . . . . . . . . . . . . . . 6
47 6. Byte order mark (BOM) . . . . . . . . . . . . . . . . . . . . 6
48 7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
49 8. MIME registration . . . . . . . . . . . . . . . . . . . . . . 9
50 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
51 10. Security Considerations . . . . . . . . . . . . . . . . . . . 10
52 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
53 12. Changes from RFC 2279 . . . . . . . . . . . . . . . . . . . . 11
54 13. Normative References . . . . . . . . . . . . . . . . . . . . . 12
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60RFC 3629 UTF-8 November 2003
63 14. Informative References . . . . . . . . . . . . . . . . . . . . 12
64 15. URI's . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
65 16. Intellectual Property Statement . . . . . . . . . . . . . . . 13
66 17. Author's Address . . . . . . . . . . . . . . . . . . . . . . . 13
67 18. Full Copyright Statement . . . . . . . . . . . . . . . . . . . 14
71 ISO/IEC 10646 [ISO.10646] defines a large character set called the
72 Universal Character Set (UCS), which encompasses most of the world's
73 writing systems. The same set of characters is defined by the
74 Unicode standard [UNICODE], which further defines additional
75 character properties and other application details of great interest
76 to implementers. Up to the present time, changes in Unicode and
77 amendments and additions to ISO/IEC 10646 have tracked each other, so
78 that the character repertoires and code point assignments have
79 remained in sync. The relevant standardization committees have
80 committed to maintain this very useful synchronism.
82 ISO/IEC 10646 and Unicode define several encoding forms of their
83 common repertoire: UTF-8, UCS-2, UTF-16, UCS-4 and UTF-32. In an
84 encoding form, each character is represented as one or more encoding
85 units. All standard UCS encoding forms except UTF-8 have an encoding
86 unit larger than one octet, making them hard to use in many current
87 applications and protocols that assume 8 or even 7 bit characters.
89 UTF-8, the object of this memo, has a one-octet encoding unit. It
90 uses all bits of an octet, but has the quality of preserving the full
91 US-ASCII [US-ASCII] range: US-ASCII characters are encoded in one
92 octet having the normal US-ASCII value, and any octet with such a
93 value can only stand for a US-ASCII character, and nothing else.
95 UTF-8 encodes UCS characters as a varying number of octets, where the
96 number of octets, and the value of each, depend on the integer value
97 assigned to the character in ISO/IEC 10646 (the character number,
98 a.k.a. code position, code point or Unicode scalar value). This
99 encoding form has the following characteristics (all values are in
102 o Character numbers from U+0000 to U+007F (US-ASCII repertoire)
103 correspond to octets 00 to 7F (7 bit US-ASCII values). A direct
104 consequence is that a plain ASCII string is also a valid UTF-8
114Yergeau Standards Track [Page 2]
116RFC 3629 UTF-8 November 2003
119 o US-ASCII octet values do not appear otherwise in a UTF-8 encoded
120 character stream. This provides compatibility with file systems
121 or other software (e.g., the printf() function in C libraries)
122 that parse based on US-ASCII values but are transparent to other
125 o Round-trip conversion is easy between UTF-8 and other encoding
128 o The first octet of a multi-octet sequence indicates the number of
129 octets in the sequence.
131 o The octet values C0, C1, F5 to FF never appear.
133 o Character boundaries are easily found from anywhere in an octet
136 o The byte-value lexicographic sorting order of UTF-8 strings is the
137 same as if ordered by character numbers. Of course this is of
138 limited interest since a sort order based on character numbers is
139 almost never culturally valid.
141 o The Boyer-Moore fast search algorithm can be used with UTF-8 data.
143 o UTF-8 strings can be fairly reliably recognized as such by a
144 simple algorithm, i.e., the probability that a string of
145 characters in any other encoding appears as valid UTF-8 is low,
146 diminishing with increasing string length.
148 UTF-8 was devised in September 1992 by Ken Thompson, guided by design
149 criteria specified by Rob Pike, with the objective of defining a UCS
150 transformation format usable in the Plan9 operating system in a non-
151 disruptive manner. Thompson's design was stewarded through
152 standardization by the X/Open Joint Internationalization Group XOJIG
153 (see [FSS_UTF]), bearing the names FSS-UTF (variant FSS/UTF), UTF-2
154 and finally UTF-8 along the way.
1562. Notational conventions
158 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
159 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
160 document are to be interpreted as described in [RFC2119].
162 UCS characters are designated by the U+HHHH notation, where HHHH is a
163 string of from 4 to 6 hexadecimal digits representing the character
164 number in ISO/IEC 10646.
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172RFC 3629 UTF-8 November 2003
177 UTF-8 is defined by the Unicode Standard [UNICODE]. Descriptions and
178 formulae can also be found in Annex D of ISO/IEC 10646-1 [ISO.10646]
180 In UTF-8, characters from the U+0000..U+10FFFF range (the UTF-16
181 accessible range) are encoded using sequences of 1 to 4 octets. The
182 only octet of a "sequence" of one has the higher-order bit set to 0,
183 the remaining 7 bits being used to encode the character number. In a
184 sequence of n octets, n>1, the initial octet has the n higher-order
185 bits set to 1, followed by a bit set to 0. The remaining bit(s) of
186 that octet contain bits from the number of the character to be
187 encoded. The following octet(s) all have the higher-order bit set to
188 1 and the following bit set to 0, leaving 6 bits in each to contain
189 bits from the character to be encoded.
191 The table below summarizes the format of these different octet types.
192 The letter x indicates bits available for encoding bits of the
195 Char. number range | UTF-8 octet sequence
196 (hexadecimal) | (binary)
197 --------------------+---------------------------------------------
198 0000 0000-0000 007F | 0xxxxxxx
199 0000 0080-0000 07FF | 110xxxxx 10xxxxxx
200 0000 0800-0000 FFFF | 1110xxxx 10xxxxxx 10xxxxxx
201 0001 0000-0010 FFFF | 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
203 Encoding a character to UTF-8 proceeds as follows:
205 1. Determine the number of octets required from the character number
206 and the first column of the table above. It is important to note
207 that the rows of the table are mutually exclusive, i.e., there is
208 only one valid way to encode a given character.
210 2. Prepare the high-order bits of the octets as per the second
213 3. Fill in the bits marked x from the bits of the character number,
214 expressed in binary. Start by putting the lowest-order bit of
215 the character number in the lowest-order position of the last
216 octet of the sequence, then put the next higher-order bit of the
217 character number in the next higher-order position of that octet,
218 etc. When the x bits of the last octet are filled in, move on to
219 the next to last octet, then to the preceding one, etc. until all
220 x bits are filled in.
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228RFC 3629 UTF-8 November 2003
231 The definition of UTF-8 prohibits encoding character numbers between
232 U+D800 and U+DFFF, which are reserved for use with the UTF-16
233 encoding form (as surrogate pairs) and do not directly represent
234 characters. When encoding in UTF-8 from UTF-16 data, it is necessary
235 to first decode the UTF-16 data to obtain character numbers, which
236 are then encoded in UTF-8 as described above. This contrasts with
237 CESU-8 [CESU-8], which is a UTF-8-like encoding that is not meant for
238 use on the Internet. CESU-8 operates similarly to UTF-8 but encodes
239 the UTF-16 code values (16-bit quantities) instead of the character
240 number (code point). This leads to different results for character
241 numbers above 0xFFFF; the CESU-8 encoding of those characters is NOT
244 Decoding a UTF-8 character proceeds as follows:
246 1. Initialize a binary number with all bits set to 0. Up to 21 bits
249 2. Determine which bits encode the character number from the number
250 of octets in the sequence and the second column of the table
251 above (the bits marked x).
253 3. Distribute the bits from the sequence to the binary number, first
254 the lower-order bits from the last octet of the sequence and
255 proceeding to the left until no x bits are left. The binary
256 number is now equal to the character number.
258 Implementations of the decoding algorithm above MUST protect against
259 decoding invalid sequences. For instance, a naive implementation may
260 decode the overlong UTF-8 sequence C0 80 into the character U+0000,
261 or the surrogate pair ED A1 8C ED BE B4 into U+233B4. Decoding
262 invalid sequences may have security consequences or cause other
263 problems. See Security Considerations (Section 10) below.
2654. Syntax of UTF-8 Byte Sequences
267 For the convenience of implementors using ABNF, a definition of UTF-8
268 in ABNF syntax is given here.
270 A UTF-8 string is a sequence of octets representing a sequence of UCS
271 characters. An octet sequence is valid UTF-8 only if it matches the
272 following syntax, which is derived from the rules for encoding UTF-8
273 and is expressed in the ABNF of [RFC2234].
275 UTF8-octets = *( UTF8-char )
276 UTF8-char = UTF8-1 / UTF8-2 / UTF8-3 / UTF8-4
278 UTF8-2 = %xC2-DF UTF8-tail
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284RFC 3629 UTF-8 November 2003
287 UTF8-3 = %xE0 %xA0-BF UTF8-tail / %xE1-EC 2( UTF8-tail ) /
288 %xED %x80-9F UTF8-tail / %xEE-EF 2( UTF8-tail )
289 UTF8-4 = %xF0 %x90-BF 2( UTF8-tail ) / %xF1-F3 3( UTF8-tail ) /
290 %xF4 %x80-8F 2( UTF8-tail )
293 NOTE -- The authoritative definition of UTF-8 is in [UNICODE]. This
294 grammar is believed to describe the same thing Unicode describes, but
295 does not claim to be authoritative. Implementors are urged to rely
296 on the authoritative source, rather than on this ABNF.
2985. Versions of the standards
300 ISO/IEC 10646 is updated from time to time by publication of
301 amendments and additional parts; similarly, new versions of the
302 Unicode standard are published over time. Each new version obsoletes
303 and replaces the previous one, but implementations, and more
304 significantly data, are not updated instantly.
306 In general, the changes amount to adding new characters, which does
307 not pose particular problems with old data. In 1996, Amendment 5 to
308 the 1993 edition of ISO/IEC 10646 and Unicode 2.0 moved and expanded
309 the Korean Hangul block, thereby making any previous data containing
310 Hangul characters invalid under the new version. Unicode 2.0 has the
311 same difference from Unicode 1.1. The justification for allowing
312 such an incompatible change was that there were no major
313 implementations and no significant amounts of data containing Hangul.
314 The incident has been dubbed the "Korean mess", and the relevant
315 committees have pledged to never, ever again make such an
316 incompatible change (see Unicode Consortium Policies [1]).
318 New versions, and in particular any incompatible changes, have
319 consequences regarding MIME charset labels, to be discussed in MIME
320 registration (Section 8).
3226. Byte order mark (BOM)
324 The UCS character U+FEFF "ZERO WIDTH NO-BREAK SPACE" is also known
325 informally as "BYTE ORDER MARK" (abbreviated "BOM"). This character
326 can be used as a genuine "ZERO WIDTH NO-BREAK SPACE" within text, but
327 the BOM name hints at a second possible usage of the character: to
328 prepend a U+FEFF character to a stream of UCS characters as a
329 "signature". A receiver of such a serialized stream may then use the
330 initial character as a hint that the stream consists of UCS
331 characters and also to recognize which UCS encoding is involved and,
332 with encodings having a multi-octet encoding unit, as a way to
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340RFC 3629 UTF-8 November 2003
343 recognize the serialization order of the octets. UTF-8 having a
344 single-octet encoding unit, this last function is useless and the BOM
345 will always appear as the octet sequence EF BB BF.
347 It is important to understand that the character U+FEFF appearing at
348 any position other than the beginning of a stream MUST be interpreted
349 with the semantics for the zero-width non-breaking space, and MUST
350 NOT be interpreted as a signature. When interpreted as a signature,
351 the Unicode standard suggests than an initial U+FEFF character may be
352 stripped before processing the text. Such stripping is necessary in
353 some cases (e.g., when concatenating two strings, because otherwise
354 the resulting string may contain an unintended "ZERO WIDTH NO-BREAK
355 SPACE" at the connection point), but might affect an external process
356 at a different layer (such as a digital signature or a count of the
357 characters) that is relying on the presence of all characters in the
358 stream. It is therefore RECOMMENDED to avoid stripping an initial
359 U+FEFF interpreted as a signature without a good reason, to ignore it
360 instead of stripping it when appropriate (such as for display) and to
361 strip it only when really necessary.
363 U+FEFF in the first position of a stream MAY be interpreted as a
364 zero-width non-breaking space, and is not always a signature. In an
365 attempt at diminishing this uncertainty, Unicode 3.2 adds a new
366 character, U+2060 "WORD JOINER", with exactly the same semantics and
367 usage as U+FEFF except for the signature function, and strongly
368 recommends its exclusive use for expressing word-joining semantics.
369 Eventually, following this recommendation will make it all but
370 certain that any initial U+FEFF is a signature, not an intended "ZERO
371 WIDTH NO-BREAK SPACE".
373 In the meantime, the uncertainty unfortunately remains and may affect
374 Internet protocols. Protocol specifications MAY restrict usage of
375 U+FEFF as a signature in order to reduce or eliminate the potential
376 ill effects of this uncertainty. In the interest of striking a
377 balance between the advantages (reduction of uncertainty) and
378 drawbacks (loss of the signature function) of such restrictions, it
379 is useful to distinguish a few cases:
381 o A protocol SHOULD forbid use of U+FEFF as a signature for those
382 textual protocol elements that the protocol mandates to be always
383 UTF-8, the signature function being totally useless in those
386 o A protocol SHOULD also forbid use of U+FEFF as a signature for
387 those textual protocol elements for which the protocol provides
388 character encoding identification mechanisms, when it is expected
389 that implementations of the protocol will be in a position to
390 always use the mechanisms properly. This will be the case when
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396RFC 3629 UTF-8 November 2003
399 the protocol elements are maintained tightly under the control of
400 the implementation from the time of their creation to the time of
401 their (properly labeled) transmission.
403 o A protocol SHOULD NOT forbid use of U+FEFF as a signature for
404 those textual protocol elements for which the protocol does not
405 provide character encoding identification mechanisms, when a ban
406 would be unenforceable, or when it is expected that
407 implementations of the protocol will not be in a position to
408 always use the mechanisms properly. The latter two cases are
409 likely to occur with larger protocol elements such as MIME
410 entities, especially when implementations of the protocol will
411 obtain such entities from file systems, from protocols that do not
412 have encoding identification mechanisms for payloads (such as FTP)
413 or from other protocols that do not guarantee proper
414 identification of character encoding (such as HTTP).
416 When a protocol forbids use of U+FEFF as a signature for a certain
417 protocol element, then any initial U+FEFF in that protocol element
418 MUST be interpreted as a "ZERO WIDTH NO-BREAK SPACE". When a
419 protocol does NOT forbid use of U+FEFF as a signature for a certain
420 protocol element, then implementations SHOULD be prepared to handle a
421 signature in that element and react appropriately: using the
422 signature to identify the character encoding as necessary and
423 stripping or ignoring the signature as appropriate.
427 The character sequence U+0041 U+2262 U+0391 U+002E "A<NOT IDENTICAL
428 TO><ALPHA>." is encoded in UTF-8 as follows:
434 The character sequence U+D55C U+AD6D U+C5B4 (Korean "hangugeo",
435 meaning "the Korean language") is encoded in UTF-8 as follows:
437 --------+--------+--------
438 ED 95 9C EA B5 AD EC 96 B4
439 --------+--------+--------
441 The character sequence U+65E5 U+672C U+8A9E (Japanese "nihongo",
442 meaning "the Japanese language") is encoded in UTF-8 as follows:
444 --------+--------+--------
445 E6 97 A5 E6 9C AC E8 AA 9E
446 --------+--------+--------
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452RFC 3629 UTF-8 November 2003
455 The character U+233B4 (a Chinese character meaning 'stump of tree'),
456 prepended with a UTF-8 BOM, is encoded in UTF-8 as follows:
464 This memo serves as the basis for registration of the MIME charset
465 parameter for UTF-8, according to [RFC2978]. The charset parameter
466 value is "UTF-8". This string labels media types containing text
467 consisting of characters from the repertoire of ISO/IEC 10646
468 including all amendments at least up to amendment 5 of the 1993
469 edition (Korean block), encoded to a sequence of octets using the
470 encoding scheme outlined above. UTF-8 is suitable for use in MIME
471 content types under the "text" top-level type.
473 It is noteworthy that the label "UTF-8" does not contain a version
474 identification, referring generically to ISO/IEC 10646. This is
475 intentional, the rationale being as follows:
477 A MIME charset label is designed to give just the information needed
478 to interpret a sequence of bytes received on the wire into a sequence
479 of characters, nothing more (see [RFC2045], section 2.2). As long as
480 a character set standard does not change incompatibly, version
481 numbers serve no purpose, because one gains nothing by learning from
482 the tag that newly assigned characters may be received that one
483 doesn't know about. The tag itself doesn't teach anything about the
484 new characters, which are going to be received anyway.
486 Hence, as long as the standards evolve compatibly, the apparent
487 advantage of having labels that identify the versions is only that,
488 apparent. But there is a disadvantage to such version-dependent
489 labels: when an older application receives data accompanied by a
490 newer, unknown label, it may fail to recognize the label and be
491 completely unable to deal with the data, whereas a generic, known
492 label would have triggered mostly correct processing of the data,
493 which may well not contain any new characters.
495 Now the "Korean mess" (ISO/IEC 10646 amendment 5) is an incompatible
496 change, in principle contradicting the appropriateness of a version
497 independent MIME charset label as described above. But the
498 compatibility problem can only appear with data containing Korean
499 Hangul characters encoded according to Unicode 1.1 (or equivalently
500 ISO/IEC 10646 before amendment 5), and there is arguably no such data
501 to worry about, this being the very reason the incompatible change
502 was deemed acceptable.
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508RFC 3629 UTF-8 November 2003
511 In practice, then, a version-independent label is warranted, provided
512 the label is understood to refer to all versions after Amendment 5,
513 and provided no incompatible change actually occurs. Should
514 incompatible changes occur in a later version of ISO/IEC 10646, the
515 MIME charset label defined here will stay aligned with the previous
516 version until and unless the IETF specifically decides otherwise.
5189. IANA Considerations
520 The entry for UTF-8 in the IANA charset registry has been updated to
52310. Security Considerations
525 Implementers of UTF-8 need to consider the security aspects of how
526 they handle illegal UTF-8 sequences. It is conceivable that in some
527 circumstances an attacker would be able to exploit an incautious
528 UTF-8 parser by sending it an octet sequence that is not permitted by
531 A particularly subtle form of this attack can be carried out against
532 a parser which performs security-critical validity checks against the
533 UTF-8 encoded form of its input, but interprets certain illegal octet
534 sequences as characters. For example, a parser might prohibit the
535 NUL character when encoded as the single-octet sequence 00, but
536 erroneously allow the illegal two-octet sequence C0 80 and interpret
537 it as a NUL character. Another example might be a parser which
538 prohibits the octet sequence 2F 2E 2E 2F ("/../"), yet permits the
539 illegal octet sequence 2F C0 AE 2E 2F. This last exploit has
540 actually been used in a widespread virus attacking Web servers in
541 2001; thus, the security threat is very real.
543 Another security issue occurs when encoding to UTF-8: the ISO/IEC
544 10646 description of UTF-8 allows encoding character numbers up to
545 U+7FFFFFFF, yielding sequences of up to 6 bytes. There is therefore
546 a risk of buffer overflow if the range of character numbers is not
547 explicitly limited to U+10FFFF or if buffer sizing doesn't take into
548 account the possibility of 5- and 6-byte sequences.
550 Security may also be impacted by a characteristic of several
551 character encodings, including UTF-8: the "same thing" (as far as a
552 user can tell) can be represented by several distinct character
553 sequences. For instance, an e with acute accent can be represented
554 by the precomposed U+00E9 E ACUTE character or by the canonically
555 equivalent sequence U+0065 U+0301 (E + COMBINING ACUTE). Even though
556 UTF-8 provides a single byte sequence for each character sequence,
557 the existence of multiple character sequences for "the same thing"
558 may have security consequences whenever string matching, indexing,
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564RFC 3629 UTF-8 November 2003
567 searching, sorting, regular expression matching and selection are
568 involved. An example would be string matching of an identifier
569 appearing in a credential and in access control list entries. This
570 issue is amenable to solutions based on Unicode Normalization Forms,
575 The following have participated in the drafting and discussion of
576 this memo: James E. Agenbroad, Harald Alvestrand, Andries Brouwer,
577 Mark Davis, Martin J. Duerst, Patrick Faltstrom, Ned Freed, David
578 Goldsmith, Tony Hansen, Edwin F. Hart, Paul Hoffman, David Hopwood,
579 Simon Josefsson, Kent Karlsson, Dan Kohn, Markus Kuhn, Michael Kung,
580 Alain LaBonte, Ira McDonald, Alexey Melnikov, MURATA Makoto, John
581 Gardiner Myers, Chris Newman, Dan Oscarsson, Roozbeh Pournader,
582 Murray Sargent, Markus Scherer, Keld Simonsen, Arnold Winkler,
583 Kenneth Whistler and Misha Wolf.
58512. Changes from RFC 2279
587 o Restricted the range of characters to 0000-10FFFF (the UTF-16
590 o Made Unicode the source of the normative definition of UTF-8,
591 keeping ISO/IEC 10646 as the reference for characters.
593 o Straightened out terminology. UTF-8 now described in terms of an
594 encoding form of the character number. UCS-2 and UCS-4 almost
597 o Turned the note warning against decoding of invalid sequences into
598 a normative MUST NOT.
600 o Added a new section about the UTF-8 BOM, with advice for
603 o Removed suggested UNICODE-1-1-UTF-8 MIME charset registration.
605 o Added an ABNF syntax for valid UTF-8 octet sequences
607 o Expanded Security Considerations section, in particular impact of
608 Unicode normalization
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620RFC 3629 UTF-8 November 2003
62313. Normative References
625 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
626 Requirement Levels", BCP 14, RFC 2119, March 1997.
628 [ISO.10646] International Organization for Standardization,
629 "Information Technology - Universal Multiple-octet coded
630 Character Set (UCS)", ISO/IEC Standard 10646, comprised
631 of ISO/IEC 10646-1:2000, "Information technology --
632 Universal Multiple-Octet Coded Character Set (UCS) --
633 Part 1: Architecture and Basic Multilingual Plane",
634 ISO/IEC 10646-2:2001, "Information technology --
635 Universal Multiple-Octet Coded Character Set (UCS) --
636 Part 2: Supplementary Planes" and ISO/IEC 10646-
637 1:2000/Amd 1:2002, "Mathematical symbols and other
640 [UNICODE] The Unicode Consortium, "The Unicode Standard -- Version
641 4.0", defined by The Unicode Standard, Version 4.0
642 (Boston, MA, Addison-Wesley, 2003. ISBN 0-321-18578-1),
643 April 2003, <http://www.unicode.org/unicode/standard/
644 versions/enumeratedversions.html#Unicode_4_0_0>.
64614. Informative References
648 [CESU-8] Phipps, T., "Unicode Technical Report #26: Compatibility
649 Encoding Scheme for UTF-16: 8-Bit (CESU-8)", UTR 26,
651 <http://www.unicode.org/unicode/reports/tr26/>.
653 [FSS_UTF] X/Open Company Ltd., "X/Open Preliminary Specification --
654 File System Safe UCS Transformation Format (FSS-UTF)",
655 May 1993, <http://wwwold.dkuug.dk/jtc1/sc22/wg20/docs/
658 [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
659 Extensions (MIME) Part One: Format of Internet Message
660 Bodies", RFC 2045, November 1996.
662 [RFC2234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
663 Specifications: ABNF", RFC 2234, November 1997.
665 [RFC2978] Freed, N. and J. Postel, "IANA Charset Registration
666 Procedures", BCP 19, RFC 2978, October 2000.
674Yergeau Standards Track [Page 12]
676RFC 3629 UTF-8 November 2003
679 [UAX15] Davis, M. and M. Duerst, "Unicode Standard Annex #15:
680 Unicode Normalization Forms", An integral part of The
681 Unicode Standard, Version 4.0.0, April 2003, <http://
682 www.unicode.org/unicode/reports/tr15>.
684 [US-ASCII] American National Standards Institute, "Coded Character
685 Set - 7-bit American Standard Code for Information
686 Interchange", ANSI X3.4, 1986.
690 [1] <http://www.unicode.org/unicode/standard/policies.html>
69216. Intellectual Property Statement
694 The IETF takes no position regarding the validity or scope of any
695 intellectual property or other rights that might be claimed to
696 pertain to the implementation or use of the technology described in
697 this document or the extent to which any license under such rights
698 might or might not be available; neither does it represent that it
699 has made any effort to identify any such rights. Information on the
700 IETF's procedures with respect to rights in standards-track and
701 standards-related documentation can be found in BCP-11. Copies of
702 claims of rights made available for publication and any assurances of
703 licenses to be made available, or the result of an attempt made to
704 obtain a general license or permission for the use of such
705 proprietary rights by implementors or users of this specification can
706 be obtained from the IETF Secretariat.
708 The IETF invites any interested party to bring to its attention any
709 copyrights, patents or patent applications, or other proprietary
710 rights which may cover technology that may be required to practice
711 this standard. Please address the information to the IETF Executive
718 100, boul. Alexis-Nihon, bureau 600
722 Phone: +1 514 747 2547
724 EMail: fyergeau@alis.com
730Yergeau Standards Track [Page 13]
732RFC 3629 UTF-8 November 2003
73518. Full Copyright Statement
737 Copyright (C) The Internet Society (2003). All Rights Reserved.
739 This document and translations of it may be copied and furnished to
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