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Network Working Group                                        P. HoffmanRequest for Comments: 2781                     Internet Mail ConsortiumCategory: Informational                                      F. Yergeau                                                      Alis Technologies                                                          February 2000UTF-16, an encoding of ISO 10646Status of this Memo   This memo provides information for the Internet community.  It does   not specify an Internet standard of any kind.  Distribution of this   memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2000).  All Rights Reserved.1. Introduction   This document describes the UTF-16 encoding of Unicode/ISO-10646,   addresses the issues of serializing UTF-16 as an octet stream for   transmission over the Internet, discusses MIME charset naming as   described in [CHARSET-REG], and contains the registration for three   MIME charset parameter values: UTF-16BE (big-endian), UTF-16LE   (little-endian), and UTF-16.1.1 Background and motivation   The Unicode Standard [UNICODE] and ISO/IEC 10646 [ISO-10646] jointly   define a coded character set (CCS), hereafter referred to as Unicode,   which encompasses most of the world's writing systems [WORKSHOP].   UTF-16, the object of this specification, is one of the standard ways   of encoding Unicode character data; it has the characteristics of   encoding all currently defined characters (in plane 0, the BMP) in   exactly two octets and of being able to encode all other characters   likely to be defined (the next 16 planes) in exactly four octets.   The Unicode Standard further defines additional character properties   and other application details of great interest to implementors. Up   to the present time, changes in Unicode and amendments to ISO/IEC   10646 have tracked each other, so that the character repertoires and   code point assignments have remained in sync. The relevant   standardization committees have committed to maintain this very   useful synchronism, as well as not to assign characters outside of   the 17 planes accessible to UTF-16.Hoffman & Yergeau            Informational                      [Page 1]

RFC 2781            UTF-16, an encoding of ISO 10646       February 2000   The IETF policy on character sets and languages [CHARPOLICY] says   that IETF protocols MUST be able to use the UTF-8 character encoding   scheme [UTF-8]. Some products and network standards already specify   UTF-16, making it an important encoding for the Internet. This   document is not an update to the [CHARPOLICY] document, only a   description of the UTF-16 encoding.1.2 Terminology   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this   document are to be interpreted as described inRFC 2119 [MUSTSHOULD].   Throughout this document, character values are shown in hexadecimal   notation. For example, "0x013C" is the character whose value is the   character assigned the integer value 316 (decimal) in the CCS.2. UTF-16 definition   UTF-16 is described in the Unicode Standard, version 3.0 [UNICODE].   The definitive reference is Annex Q of ISO/IEC 10646-1 [ISO-10646].   The rest of this section summarizes the definition is simple terms.   In ISO 10646, each character is assigned a number, which Unicode   calls the Unicode scalar value. This number is the same as the UCS-4   value of the character, and this document will refer to it as the   "character value" for brevity. In the UTF-16 encoding, characters are   represented using either one or two unsigned 16-bit integers,   depending on the character value. Serialization of these integers for   transmission as a byte stream is discussed inSection 3.   The rules for how characters are encoded in UTF-16 are:   -  Characters with values less than 0x10000 are represented as a      single 16-bit integer with a value equal to that of the character      number.   -  Characters with values between 0x10000 and 0x10FFFF are      represented by a 16-bit integer with a value between 0xD800 and      0xDBFF (within the so-called high-half zone or high surrogate      area) followed by a 16-bit integer with a value between 0xDC00 and      0xDFFF (within the so-called low-half zone or low surrogate area).   -  Characters with values greater than 0x10FFFF cannot be encoded in      UTF-16.   Note: Values between 0xD800 and 0xDFFF are specifically reserved for   use with UTF-16, and don't have any characters assigned to them.Hoffman & Yergeau            Informational                      [Page 2]

RFC 2781            UTF-16, an encoding of ISO 10646       February 20002.1 Encoding UTF-16   Encoding of a single character from an ISO 10646 character value to   UTF-16 proceeds as follows. Let U be the character number, no greater   than 0x10FFFF.   1) If U < 0x10000, encode U as a 16-bit unsigned integer and      terminate.   2) Let U' = U - 0x10000. Because U is less than or equal to 0x10FFFF,      U' must be less than or equal to 0xFFFFF. That is, U' can be      represented in 20 bits.   3) Initialize two 16-bit unsigned integers, W1 and W2, to 0xD800 and      0xDC00, respectively. These integers each have 10 bits free to      encode the character value, for a total of 20 bits.   4) Assign the 10 high-order bits of the 20-bit U' to the 10 low-order      bits of W1 and the 10 low-order bits of U' to the 10 low-order      bits of W2. Terminate.   Graphically, steps 2 through 4 look like:   U' = yyyyyyyyyyxxxxxxxxxx   W1 = 110110yyyyyyyyyy   W2 = 110111xxxxxxxxxx2.2 Decoding UTF-16   Decoding of a single character from UTF-16 to an ISO 10646 character   value proceeds as follows. Let W1 be the next 16-bit integer in the   sequence of integers representing the text. Let W2 be the (eventual)   next integer following W1.   1) If W1 < 0xD800 or W1 > 0xDFFF, the character value U is the value      of W1. Terminate.   2) Determine if W1 is between 0xD800 and 0xDBFF. If not, the sequence      is in error and no valid character can be obtained using W1.      Terminate.   3) If there is no W2 (that is, the sequence ends with W1), or if W2      is not between 0xDC00 and 0xDFFF, the sequence is in error.      Terminate.   4) Construct a 20-bit unsigned integer U', taking the 10 low-order      bits of W1 as its 10 high-order bits and the 10 low-order bits of      W2 as its 10 low-order bits.Hoffman & Yergeau            Informational                      [Page 3]

RFC 2781            UTF-16, an encoding of ISO 10646       February 2000   5) Add 0x10000 to U' to obtain the character value U. Terminate.   Note that steps 2 and 3 indicate errors. Error recovery is not   specified by this document. When terminating with an error in steps 2   and 3, it may be wise to set U to the value of W1 to help the caller   diagnose the error and not lose information. Also note that a string   decoding algorithm, as opposed to the single-character decoding   described above, need not terminate upon detection of an error, if   proper error reporting and/or recovery is provided.3. Labelling UTF-16 textAppendix A of this specification contains registrations for three   MIME charsets: "UTF-16BE", "UTF-16LE", and "UTF-16". MIME charsets   represent the combination of a CCS (a coded character set) and a CES   (a character encoding scheme). Here the CCS is Unicode/ISO 10646 and   the CES is the same in all three cases, except for the serialization   order of the octets in each character, and the external determination   of which serialization is used.   This section describes which of the three labels to apply to a stream   of text.Section 4 describes how to interpret the labels on a stream   of text.3.1 Definition of big-endian and little-endian   Historically, computer hardware has processed two-octet entities such   as 16-bit integers in one of two ways. So-called "big-endian"   hardware handles two-octet entities with the higher-order octet   first, that is at the lower address in memory; when written out to   disk or to a network interface (serializing), the high-order octet   thus appears first in the data stream. On the other hand, "Little-   endian" hardware handles two-octet entities with the lower-order   octet first. Hardware of both kinds is common today.   For example, the unsigned 16-bit integer that represents the decimal   number 258 is 0x0102. The big-endian serialization of that number is   the octet 0x01 followed by the octet 0x02. The little-endian   serialization of that number is the octet 0x02 followed by the octet   0x01. The following C code fragment demonstrates a way to write 16-   bit quantities to a file in big-endian order, irrespective of the   hardware's native byte order.  void write_be(unsigned short u, FILE f)  /* assume short is 16 bits */  {    putc(u >> 8,   f);                     /* output high-order byte */    putc(u & 0xFF, f);                     /* then low-order */  }Hoffman & Yergeau            Informational                      [Page 4]

RFC 2781            UTF-16, an encoding of ISO 10646       February 2000   The term "network byte order" has been used in many RFCs to indicate   big-endian serialization, although that term has yet to be formally   defined in a standards-track document. Although ISO 10646 prefers   big-endian serialization (section 6.3 of [ISO-10646]), little-endian   order is also sometimes used on the Internet.3.2 Byte order mark (BOM)   The Unicode Standard and ISO 10646 define the character "ZERO WIDTH   NON-BREAKING SPACE" (0xFEFF), which is also known informally as "BYTE   ORDER MARK" (abbreviated "BOM"). The latter name hints at a second   possible usage of the character, in addition to its normal use as a   genuine "ZERO WIDTH NON-BREAKING SPACE" within text. This usage,   suggested by Unicodesection 2.4 and ISO 10646 Annex F (informative),   is to prepend a 0xFEFF character to a stream of Unicode characters as   a "signature"; a receiver of such a serialized stream may then use   the initial character both as a hint that the stream consists of   Unicode characters and as a way to recognize the serialization order.   In serialized UTF-16 prepended with such a signature, the order is   big-endian if the first two octets are 0xFE followed by 0xFF; if they   are 0xFF followed by 0xFE, the order is little-endian. Note that   0xFFFE is not a Unicode character, precisely to preserve the   usefulness of 0xFEFF as a byte-order mark.   It is important to understand that the character 0xFEFF appearing at   any position other than the beginning of a stream MUST be interpreted   with the semantics for the zero-width non-breaking space, and MUST   NOT be interpreted as a byte-order mark. The contrapositive of that   statement is not always true: the character 0xFEFF in the first   position of a stream MAY be interpreted as a zero-width non-breaking   space, and is not always a byte-order mark. For example, if a process   splits a UTF-16 string into many parts, a part might begin with   0xFEFF because there was a zero-width non-breaking space at the   beginning of that substring.   The Unicode standard further suggests than an initial 0xFEFF   character may be stripped before processing the text, the rationale   being that such a character in initial position may be an artifact of   the encoding (an encoding signature), not a genuine intended "ZERO   WIDTH NON-BREAKING SPACE". Note that such stripping might affect an   external process at a different layer (such as a digital signature or   a count of the characters) that is relying on the presence of all   characters in the stream.   In particular, in UTF-16 plain text it is likely, but not certain,   that an initial 0xFEFF is a signature. When concatenating two   strings, it is important to strip out those signatures, because   otherwise the resulting string may contain an unintended "ZERO WIDTHHoffman & Yergeau            Informational                      [Page 5]

RFC 2781            UTF-16, an encoding of ISO 10646       February 2000   NON-BREAKING SPACE" at the connection point. Also, some   specifications mandate an initial 0xFEFF character in objects   labelled as UTF-16 and specify that this signature is not part of the   object.3.3 Choosing a label for UTF-16 text   Any labelling application that uses UTF-16 character encoding, and   explicitly labels the text, and knows the serialization order of the   characters in text, SHOULD label the text as either "UTF-16BE" or   "UTF-16LE", whichever is appropriate based on the endianness of the   text. This allows applications processing the text, but unable to   look inside the text, to know the serialization definitively.   Text in the "UTF-16BE" charset MUST be serialized with the octets   which make up a single 16-bit UTF-16 value in big-endian order.   Systems labelling UTF-16BE text MUST NOT prepend a BOM to the text.   Text in the "UTF-16LE" charset MUST be serialized with the octets   which make up a single 16-bit UTF-16 value in little-endian order.   Systems labelling UTF-16LE text MUST NOT prepend a BOM to the text.   Any labelling application that uses UTF-16 character encoding, and   puts an explicit charset label on the text, and does not know the   serialization order of the characters in text, MUST label the text as   "UTF-16", and SHOULD make sure the text starts with 0xFEFF.   An exception to the "SHOULD" rule of using "UTF-16BE" or "UTF-16LE"   would occur with document formats that mandate a BOM in UTF-16 text,   thereby requiring the use of the "UTF-16" tag only.4. Interpreting text labels   When a program sees text labelled as "UTF-16BE", "UTF-16LE", or   "UTF-16", it can make some assumptions, based on the labelling rules   given in the previous section. These assumptions allow the program to   then process the text.4.1 Interpreting text labelled as UTF-16BE   Text labelled "UTF-16BE" can always be interpreted as being big-   endian.  The detection of an initial BOM does not affect de-   serialization of text labelled as UTF-16BE. Finding 0xFF followed by   0xFE is an error since there is no Unicode character 0xFFFE.Hoffman & Yergeau            Informational                      [Page 6]

RFC 2781            UTF-16, an encoding of ISO 10646       February 20004.2 Interpreting text labelled as UTF-16LE   Text labelled "UTF-16LE" can always be interpreted as being little-   endian. The detection of an initial BOM does not affect de-   serialization of text labelled as UTF-16LE. Finding 0xFE followed by   0xFF is an error since there is no Unicode character 0xFFFE, which   would be the interpretation of those octets under little-endian   order.4.3 Interpreting text labelled as UTF-16   Text labelled with the "UTF-16" charset might be serialized in either   big-endian or little-endian order. If the first two octets of the   text is 0xFE followed by 0xFF, then the text can be interpreted as   being big-endian. If the first two octets of the text is 0xFF   followed by 0xFE, then the text can be interpreted as being little-   endian. If the first two octets of the text is not 0xFE followed by   0xFF, and is not 0xFF followed by 0xFE, then the text SHOULD be   interpreted as being big-endian.   All applications that process text with the "UTF-16" charset label   MUST be able to read at least the first two octets of the text and be   able to process those octets in order to determine the serialization   order of the text. Applications that process text with the "UTF-16"   charset label MUST NOT assume the serialization without first   checking the first two octets to see if they are a big-endian BOM, a   little-endian BOM, or not a BOM. All applications that process text   with the "UTF-16" charset label MUST be able to interpret both big-   endian and little-endian text.5. Examples   For the sake of example, let's suppose that there is a hieroglyphic   character representing the Egyptian god Ra with character value   0x12345 (this character does not exist at present in Unicode).   The examples here all evaluate to the phrase:   *=Ra   where the "*" represents the Ra hieroglyph (0x12345).   Text labelled with UTF-16BE, without a BOM:   D8 08 DF 45 00 3D 00 52 00 61   Text labelled with UTF-16LE, without a BOM:   08 D8 45 DF 3D 00 52 00 61 00Hoffman & Yergeau            Informational                      [Page 7]

RFC 2781            UTF-16, an encoding of ISO 10646       February 2000   Big-endian text labelled with UTF-16, with a BOM:   FE FF D8 08 DF 45 00 3D 00 52 00 61   Little-endian text labelled with UTF-16, with a BOM:   FF FE 08 D8 45 DF 3D 00 52 00 61 006. Versions of the standards   ISO/IEC 10646 is updated from time to time by published amendments;   similarly, different versions of the Unicode standard exist: 1.0,   1.1, 2.0, 2.1, and 3.0 as of this writing. Each new version replaces   the previous one, but implementations, and more significantly data,   are not updated instantly.   In general, the changes amount to adding new characters, which does   not pose particular problems with old data. Amendment 5 to ISO/IEC   10646, however, has moved and expanded the Korean Hangul block,   thereby making any previous data containing Hangul characters invalid   under the new version. Unicode 2.0 has the same difference from   Unicode 1.1. The official justification for allowing such an   incompatible change was that no significant implementations and data   containing Hangul existed, a statement that is likely to be true but   remains unprovable. The incident has been dubbed the "Korean mess",   and the relevant committees have pledged to never, ever again make   such an incompatible change.   New versions, and in particular any incompatible changes, have   consequences regarding MIME character encoding labels, to be   discussed inAppendix A.7. IANA Considerations   IANA is to register the character sets found in Appendixes A.1, A.2,   and A.3 according toRFC 2278, using registration templates found in   those appendixes.8. Security Considerations   UTF-16 is based on the ISO 10646 character set, which is frequently   being added to, as described inSection 6 andAppendix A of this   document. Processors must be able to handle characters that are not   defined at the time that the processor was created in such a way as   to not allow an attacker to harm a recipient by including unknown   characters.   Processors that handle any type of text, including text encoded as   UTF-16, must be vigilant in checking for control characters that   might reprogram a display terminal or keyboard. Similarly, processorsHoffman & Yergeau            Informational                      [Page 8]

RFC 2781            UTF-16, an encoding of ISO 10646       February 2000   that interpret text entities (such as looking for embedded   programming code), must be careful not to execute the code without   first alerting the recipient.   Text in UTF-16 may contain special characters, such as the OBJECT   REPLACEMENT CHARACTER (0xFFFC), that might cause external processing,   depending on the interpretation of the processing program and the   availability of an external data stream that would be executed. This   external processing may have side-effects that allow the sender of a   message to attack the receiving system.   Implementors of UTF-16 need to consider the security aspects of how   they handle illegal UTF-16 sequences (that is, sequences involving   surrogate pairs that have illegal values or unpaired surrogates). It   is conceivable that in some circumstances an attacker would be able   to exploit an incautious UTF-16 parser by sending it an octet   sequence that is not permitted by the UTF-16 syntax, causing it to   behave in some anomalous fashion.9. References   [CHARPOLICY]  Alvestrand, H., "IETF Policy on Character Sets and                 Languages",BCP 18,RFC 2277, January 1998.   [CHARSET-REG] Freed, N. and J. Postel, "IANA Charset Registration                 Procedures",BCP 19,RFC 2278, January 1998.   [HTTP-1.1]    Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,                 Masinter, L., Leach, P. and T. Berners-Lee, "Hypertext                 Transfer Protocol -- HTTP/1.1",RFC 2616, June 1999.   [ISO-10646]   ISO/IEC 10646-1:1993. International Standard --                 Information technology -- Universal Multiple-Octet                 Coded Character Set (UCS) -- Part 1: Architecture and                 Basic Multilingual Plane. 22 amendments and two                 technical corrigenda have been published up to now.                 UTF-16 is described in Annex Q, published as Amendment                 1. Many other amendments are currently at various                 stages of standardization. A second edition is in                 preparation, probably to be published in 2000; in this                 new edition, UTF-16 will probably be described in Annex                 C.   [MUSTSHOULD]  Bradner, S., "Key words for use in RFCs to Indicate                 Requirement Levels",BCP 14,RFC 2119, March 1997.   [UNICODE]     The Unicode Consortium, "The Unicode Standard --                 Version 3.0", ISBN 0-201-61633-5. Described atHoffman & Yergeau            Informational                      [Page 9]

RFC 2781            UTF-16, an encoding of ISO 10646       February 2000   <http://www.unicode.org/unicode/standard/versions/Unicode3.0.html>.   [UTF-8]       Yergeau, F., "UTF-8, a transformation format of ISO                 10646",RFC 2279, January 1998.   [WORKSHOP]    Weider, C., Preston, C., Simonsen, K., Alvestrand, H.,                 Atkinson, R., Crispin., M. and P. Svanberg, "Report of                 the IAB Character Set Workshop",RFC 2130, April 1997.10. Acknowledgments   Deborah Goldsmith wrote a great deal of the initial wording for this   specification. Martin Duerst proposed numerous significant changes.   Other significant contributors include:   Mati Allouche   Walt Daniels   Mark Davis   Ned Freed   Asmus Freytag   Lloyd Honomichl   Dan Kegel   Murata Makoto   Larry Masinter   Markus Scherer   Keld Simonsen   Ken Whistler   Some of the text in this specification was copied from [UTF-8], and   that document was worked on by many people. Please see the   acknowledgments section in that document for more people who may have   contributed indirectly to this document.Hoffman & Yergeau            Informational                     [Page 10]

RFC 2781            UTF-16, an encoding of ISO 10646       February 2000A. Charset registrations   This memo is meant to serve as the basis for registration of three   MIME charsets [CHARSET-REG]. The proposed charsets are "UTF-16BE",   "UTF-16LE", and "UTF-16". These strings label objects containing text   consisting of characters from the repertoire of ISO/IEC 10646   including all amendments at least up to amendment 5 (Korean block),   encoded to a sequence of octets using the encoding and serialization   schemes outlined above.   Note that "UTF-16BE", "UTF-16LE", and "UTF-16" are NOT suitable for   use in media types under the "text" top-level type, because they do   not encode line endings in the way required for MIME "text" media   types. An exception to this is HTTP, which uses a MIME-like   mechanism, but is exempt from the restrictions on the text top-level   type (seesection 19.4.2 of HTTP 1.1 [HTTP-1.1]).   It is noteworthy that the labels described here do not contain a   version identification, referring generically to ISO/IEC 10646. This   is intentional, the rationale being as follows:   A MIME charset is designed to give just the information needed to   interpret a sequence of bytes received on the wire into a sequence of   characters, nothing more (seeRFC 2045, section 2.2, in [MIME]). As   long as a character set standard does not change incompatibly,   version numbers serve no purpose, because one gains nothing by   learning from the tag that newly assigned characters may be received   that one doesn't know about. The tag itself doesn't teach anything   about the new characters, which are going to be received anyway.   Hence, as long as the standards evolve compatibly, the apparent   advantage of having labels that identify the versions is only that,   apparent. But there is a disadvantage to such version-dependent   labels: when an older application receives data accompanied by a   newer, unknown label, it may fail to recognize the label and be   completely unable to deal with the data, whereas a generic, known   label would have triggered mostly correct processing of the data,   which may well not contain any new characters.   The "Korean mess" (ISO/IEC 10646 amendment 5) is an incompatible   change, in principle contradicting the appropriateness of a version   independent MIME charset as described above. But the compatibility   problem can only appear with data containing Korean Hangul characters   encoded according to Unicode 1.1 (or equivalently ISO/IEC 10646   before amendment 5), and there is arguably no such data to worry   about, this being the very reason the incompatible change was deemed   acceptable.Hoffman & Yergeau            Informational                     [Page 11]

RFC 2781            UTF-16, an encoding of ISO 10646       February 2000   In practice, then, a version-independent label is warranted, provided   the label is understood to refer to all versions after Amendment 5,   and provided no incompatible change actually occurs. Should   incompatible changes occur in a later version of ISO/IEC 10646, the   MIME charsets defined here will stay aligned with the previous   version until and unless the IETF specifically decides otherwise.A.1 Registration for UTF-16BE   To: ietf-charsets@iana.org   Subject: Registration of new charset   Charset name(s): UTF-16BE   Published specification(s): This specification   Suitable for use in MIME content types under the   "text" top-level type: No   Person & email address to contact for further information:   Paul Hoffman <phoffman@imc.org>   Francois Yergeau <fyergeau@alis.com>A.2 Registration for UTF-16LE   To: ietf-charsets@iana.org   Subject: Registration of new charset   Charset name(s): UTF-16LE   Published specification(s): This specification   Suitable for use in MIME content types under the   "text" top-level type: No   Person & email address to contact for further information:   Paul Hoffman <phoffman@imc.org>   Francois Yergeau <fyergeau@alis.com>A.3 Registration for UTF-16   To: ietf-charsets@iana.org   Subject: Registration of new charset   Charset name(s): UTF-16   Published specification(s): This specificationHoffman & Yergeau            Informational                     [Page 12]

RFC 2781            UTF-16, an encoding of ISO 10646       February 2000   Suitable for use in MIME content types under the   "text" top-level type: No   Person & email address to contact for further information:   Paul Hoffman <phoffman@imc.org>   Francois Yergeau <fyergeau@alis.com>Authors' Addresses   Paul Hoffman   Internet Mail Consortium   127 Segre Place   Santa Cruz, CA  95060 USA   EMail: phoffman@imc.org   Francois Yergeau   Alis Technologies   100, boul. Alexis-Nihon, Suite 600   Montreal  QC  H4M 2P2 Canada   EMail: fyergeau@alis.comHoffman & Yergeau            Informational                     [Page 13]

RFC 2781            UTF-16, an encoding of ISO 10646       February 2000Full Copyright Statement   Copyright (C) The Internet Society (2000).  All Rights Reserved.   This document and translations of it may be copied and furnished to   others, and derivative works that comment on or otherwise explain it   or assist in its implementation may be prepared, copied, published   and distributed, in whole or in part, without restriction of any   kind, provided that the above copyright notice and this paragraph are   included on all such copies and derivative works.  However, this   document itself may not be modified in any way, such as by removing   the copyright notice or references to the Internet Society or other   Internet organizations, except as needed for the purpose of   developing Internet standards in which case the procedures for   copyrights defined in the Internet Standards process must be   followed, or as required to translate it into languages other than   English.   The limited permissions granted above are perpetual and will not be   revoked by the Internet Society or its successors or assigns.   This document and the information contained herein is provided on an   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Hoffman & Yergeau            Informational                     [Page 14]