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Versions: 00 rfc2047                                                    
Network Working Group                                           K. Moore
Internet-Draft                                   University of Tennessee
Expires: 1 December 1996                                     1 June 1996

        MIME (Multipurpose Internet Mail Extensions) Part Three:
              Message Header Extensions for Non-ASCII Text


                          Status of this Memo

   This document is an Internet Draft.  Internet Drafts are working
   documents of the Internet Engineering Task Force (IETF), its Areas,
   and its Working Groups.  Note that other groups may also distribute
   working documents as Internet Drafts.

   Internet-Drafts are draft documents valid for a maximum of six
   months. Internet-Drafts may be updated, replaced, or obsoleted by
   other documents at any time.  It is not appropriate to use an
   Internet-Draft as reference material or to cite one other than as a
   "working draft" or "work in progress".

   To learn the current status of any Internet-Draft, please check the
   1id-abstracts.txt listing contained in the Internet-Drafts Shadow
   Directories on ds.internic.net (US East Coast), nic.nordu.net
   (Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific

   This document is a revision of RFC 1522.  If approved by the IETF
   message format extensions working group, it will be submitted to the
   IESG as a candidate for Draft Standard status.  Distribution of this
   memo is unlimited.  Please send comments to


   STD 11, RFC 822, defines a message representation protocol specifying
   considerable detail about US-ASCII message headers, and leaves the
   message content, or message body, as flat US-ASCII text.  This set of
   documents, collectively called the Multipurpose Internet Mail
   Extensions, or MIME, redefines the format of messages to allow for

   (1) textual message bodies in character sets other than US-ASCII,

   (2) an extensible set of different formats for non-textual message

   (3) multi-part message bodies, and

   (4) textual header information in character sets other than US-ASCII.

   These documents are based on earlier work documented in RFC 934, STD

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   11, and RFC 1049, but extends and revises them.  Because RFC 822 said
   so little about message bodies, these documents are largely
   orthogonal to (rather than a revision of) RFC 822.

   This particular document is the third document in the series.  It
   describes extensions to RFC 822 to allow non-US-ASCII text data in
   Internet mail header fields.

   Other documents in this series include:

   + RFC MIME-IMB, which specifies the various headers used to describe
     the structure of MIME messages.

   + RFC MIME-IMT, which defines the general structure of the MIME media
     typing system and defines an initial set of media types,

   + RFC MIME-REG, which specifies various IANA registration procedures
     for MIME-related facilities, and

   + RFC MIME-CONF, which describes MIME conformance criteria and
     provides some illustrative examples of MIME message formats,
     acknowledgements, and the bibliography.

   These documents are revisions of RFCs 1521, 1522, and 1590, which
   themselves were revisions of RFCs 1341 and 1342.  An appendix in RFC
   MIME-CONF describes differences and changes from previous versions.

1. Introduction

   RFC MIME-IMB describes a mechanism for denoting textual body parts
   which are coded in various character sets, as well as methods for
   encoding such body parts as sequences of printable US-ASCII
   characters.  This memo describes similar techniques to allow the
   encoding of non-ASCII text in various portions of a RFC 822 [2]
   message header, in a manner which is unlikely to confuse existing
   message handling software.

   Like the encoding techniques described in RFC MIME-IMB, the
   techniques outlined here were designed to allow the use of non-ASCII
   characters in message headers in a way which is unlikely to be
   disturbed by the quirks of existing Internet mail handling programs.
   In particular, some mail relaying programs are known to (a) delete
   some message header fields while retaining others, (b) rearrange the
   order of addresses in To or Cc fields, (c) rearrange the (vertical)
   order of header fields, and/or (d) "wrap" message headers at
   different places than those in the original message.  In addition,
   some mail reading programs are known to have difficulty correctly
   parsing message headers which, while legal according to RFC 822, make
   use of backslash-quoting to "hide" special characters such as "<",
   ",", or ":", or which exploit other infrequently-used features of

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   that specification.

   While it is unfortunate that these programs do not correctly
   interpret RFC 822 headers, to "break" these programs would cause
   severe operational problems for the Internet mail system.  The
   extensions described in this memo therefore do not rely on little-
   used features of RFC 822.

   Instead, certain sequences of "ordinary" printable ASCII characters
   (known as "encoded-words") are reserved for use as encoded data.  The
   syntax of encoded-words is such that they are unlikely to
   "accidentally" appear as normal text in message headers.
   Furthermore, the characters used in encoded-words are restricted to
   those which do not have special meanings in the context in which the
   encoded-word appears.

   Generally, an "encoded-word" is a sequence of printable ASCII
   characters that begins with "=?", ends with "?=", and has two "?"s in
   between.  It specifies a character set and an encoding method, and
   also includes the original text encoded as graphic ASCII characters,
   according to the rules for that encoding method.

   A mail composer that implements this specification will provide a
   means of inputting non-ASCII text in header fields, but will
   translate these fields (or appropriate portions of these fields) into
   encoded-words before inserting them into the message header.

   A mail reader that implements this specification will recognize
   encoded-words when they appear in certain portions of the message
   header.  Instead of displaying the encoded-word "as is", it will
   reverse the encoding and display the original text in the designated
   character set.


   This memo relies heavily on notation and terms defined RFC 822 and
   RFC MIME-IMB.  In particular, the syntax for the ABNF used in this
   memo is defined in RFC 822, as well as many of the terminal or
   nonterminal symbols from RFC 822 are used in the grammar for the
   header extensions defined here.  Among the symbols defined in RFC 822
   and referenced in this memo are: 'addr-spec', 'atom', 'CHAR',
   'comment', 'CTLs', 'ctext', 'linear-white-space', 'phrase',
   'quoted-pair', 'quoted-string', 'SPACE', and 'word'.  Successful
   implementation of this protocol extension requires careful attention
   to the RFC 822 definitions of these terms.

   When the term "ASCII" appears in this memo, it refers to the "7-Bit
   American Standard Code for Information Interchange", ANSI X3.4-1986.
   The MIME charset name for this character set is "US-ASCII".  When not
   specifically referring to the MIME charset name, this document uses

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   the term "ASCII", both for brevity and for consistency with RFC 822.
   However, implementors are warned that the character set name must be
   spelled "US-ASCII" in MIME message and body part headers.

   This memo specifies a protocol for the representation of non-ASCII
   text in message headers.  It specifically DOES NOT define any
   translation between "8-bit headers" and pure ASCII headers, nor is
   any such translation assumed to be possible.

2. Syntax of encoded-words

   An 'encoded-word' is defined by the following ABNF grammar.  The
   notation of RFC 822 is used, with the exception that white space
   characters MUST NOT appear between components of an 'encoded-word'.

   encoded-word = "=?" charset "?" encoding "?" encoded-text "?="

   charset = token    ; see section 3

   encoding = token   ; see section 4

   token = 1*<Any CHAR except SPACE, CTLs, and especials>

   especials = "(" / ")" / "<" / ">" / "@" / "," / ";" / ":" / "\" /
               <"> / "/" / "[" / "]" / "?" / "." / "="

   encoded-text = 1*<Any printable ASCII character other than "?"
                     or SPACE>
                  ; (but see "Use of encoded-words in message
                  ; headers", section 5)

   Both 'encoding' and 'charset' names are case-independent.  Thus the
   charset name "ISO-8859-1" is equivalent to "iso-8859-1", and the
   encoding named "Q" may be spelled either "Q" or "q".

   An 'encoded-word' may not be more than 75 characters long, including
   'charset', 'encoding', 'encoded-text', and delimiters.  If it is
   desirable to encode more text than will fit in an 'encoded-word' of
   75 characters, multiple 'encoded-word's (separated by CRLF SPACE) may
   be used.

   While there is no limit to the length of a multiple-line header
   field, each line of a header field that contains one or more
   'encoded-word's is limited to 76 characters.

   The length restrictions are included both to ease interoperability
   through internetwork mail gateways, and to impose a limit on the
   amount of lookahead a header parser must employ (while looking for a
   final ?= delimiter) before it can decide whether a token is an
   'encoded-word' or something else.

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   IMPORTANT: 'encoded-word's are designed to be recognized as 'atom's
   by an RFC 822 parser.  As a consequence, unencoded white space
   characters (such as SPACE and HTAB) are FORBIDDEN within an
   'encoded-word'.  For example, the character sequence

      =?iso-8859-1?q?this is some text?=

   would be parsed as four 'atom's, rather than as a single 'atom' (by
   an RFC 822 parser) or 'encoded-word' (by a parser which understands
   'encoded-words').  The correct way to encode the string "this is some
   text" is to encode the SPACE characters as well, e.g.


   The characters which may appear in 'encoded-text' are further
   restricted by the rules in section 5.

3. Character sets

   The 'charset' portion of an 'encoded-word' specifies the character
   set associated with the unencoded text.  A 'charset' can be any of
   the character set names allowed in an MIME "charset" parameter of a
   "text/plain" body part, or any character set name registered with
   IANA for use with the MIME text/plain content-type.  (See [RFC
   CHARSET] for information about the MIME charset registry.)

   Some character sets use code-switching techniques to switch between
   "ASCII mode" and other modes.  If unencoded text in an 'encoded-word'
   contains a sequence which causes the charset interpreter to switch
   out of ASCII mode, it MUST contain additional control codes such that
   ASCII mode is again selected at the end of the 'encoded-word'.  (This
   rule applies separately to each 'encoded-word', including adjacent
   'encoded-word's within a single header field.)

   When there is a possibility of using more than one character set to
   represent the text in an 'encoded-word', and in the absence of
   private agreements between sender and recipients of a message, it is
   recommended that members of the ISO-8859-* series be used in
   preference to other character sets.

4. Encodings

   Initially, the legal values for "encoding" are "Q" and "B".  These
   encodings are described below.  The "Q" encoding is recommended for
   use when most of the characters to be encoded are in the ASCII
   character set; otherwise, the "B" encoding should be used.
   Nevertheless, a mail reader which claims to recognize 'encoded-word's
   MUST be able to accept either encoding for any character set which it

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   Only a subset of the printable ASCII characters may be used in
   'encoded-text'.  Space and tab characters are not allowed, so that
   the beginning and end of an 'encoded-word' are obvious.  The "?"
   character is used within an 'encoded-word' to separate the various
   portions of the 'encoded-word' from one another, and thus cannot
   appear in the 'encoded-text' portion.  Other characters are also
   illegal in certain contexts.  For example, an 'encoded-word' in a
   'phrase' preceding an address in a From header field may not contain
   any of the "specials" defined in RFC 822.  Finally, certain other
   characters are disallowed in some contexts, to ensure reliability for
   messages that pass through internetwork mail gateways.

   The "B" encoding automatically meets these requirements.  The "Q"
   encoding allows a wide range of printable characters to be used in
   non-critical locations in the message header (e.g., Subject), with
   fewer characters available for use in other locations.

   4.1. The "B" encoding

   The "B" encoding is identical to the "BASE64" encoding defined by RFC

   4.2. The "Q" encoding

   The "Q" encoding is similar to the "Quoted-Printable" content-
   transfer-encoding defined in RFC MIME-IMB.  It is designed to allow
   text containing mostly ASCII characters to be decipherable on an
   ASCII terminal without decoding.

   (1) Any 8-bit value may be represented by a "=" followed by two
       hexadecimal digits.  For example, if the character set in use
       were ISO-8859-1, the "=" character would thus be encoded as
       "=3D", and a SPACE by "=20".  (Upper case should be used for
       hexadecimal digits "A" through "F".)

   (2) The 8-bit hexadecimal value 20 (e.g., ISO-8859-1 SPACE) may be
       represented as "_" (underscore, ASCII 95.).  (This character may
       not pass through some internetwork mail gateways, but its use
       will greatly enhance readability of "Q" encoded data with mail
       readers that do not support this encoding.)  Note that the "_"
       always represents hexadecimal 20, even if the SPACE character
       occupies a different code position in the character set in use.

   (3) 8-bit values which correspond to printable ASCII characters other
       than "=", "?", and "_" (underscore), MAY be represented as those
       characters.  (But see section 5 for restrictions.)  In
       particular, SPACE and TAB MUST NOT be represented as themselves
       within encoded words.

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5. Use of encoded-words in message headers

   An 'encoded-word' may appear in a message header or body part header
   according to the following rules:

   (1) An 'encoded-word' may replace a 'text' token (as defined by RFC 822)
       in any Subject or Comments header field, any extension message
       header field, or any MIME body part field for which the field body
       is defined as '*text'.  An 'encoded-word' may also appear in any
       user-defined ("X-") message or body part header field.

       Ordinary ASCII text and 'encoded-word's may appear together in the
       same header field.  However, an 'encoded-word' that appears in a
       header field defined as '*text' MUST be separated from any adjacent
       'encoded-word' or 'text' by 'linear-white-space'.

   (2) An 'encoded-word' may appear within a 'comment' delimited by "(" and
       ")", i.e., wherever a 'ctext' is allowed.  More precisely, the RFC
       822 ABNF definition for 'comment' is amended as follows:

       comment = "(" *(ctext / quoted-pair / comment / encoded-word) ")"

       A "Q"-encoded 'encoded-word' which appears in a 'comment' MUST NOT
       contain the characters "(", ")" or "\".  In addition, an
       'encoded-word' that appears in a 'comment' MUST be separated from
       any adjacent 'encoded-word' or 'ctext' by 'linear-white-space'.

       It is important to note that 'comment's are only recognized inside
       "structured" field bodies.  In fields whose bodies are defined as
       '*text', "(" and ")" are treated as ordinary characters rather than
       comment delimiters, and rule (1) of this section applies.  (See RFC
       822, sections 3.1.2 and 3.1.3)

       NOTE IN DRAFT: It has been suggested that these rules be relaxed,
       and that any RFC 822 'special' character be allowed to appear
       adjacent to 'encoded-word's in either unstructured and structured
       field bodies.  This would create a slight incompatibility with RFC
       1522, but it may be that mail readers that understand RFC 1522 do
       not treat structured fields differently from unstructured fields

   (3) As a replacement for a 'word' entity within a 'phrase', for example,
       one that precedes an address in a From, To, or Cc header.  The ABNF
       definition for 'phrase' from RFC 822 thus becomes:

       phrase = 1*( encoded-word / word )

       In this case the set of characters that may be used in a "Q"-encoded
       'encoded-word' is restricted to: <upper and lower case ASCII
       letters, decimal digits, "!", "*", "+", "-", "/", "=", and "_"
       (underscore, ASCII 95.)>.  An 'encoded-word' that appears within a

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       'phrase' MUST be separated from any adjacent 'word', 'text' or
       'special' by 'linear-white-space'.

   These are the ONLY locations where an 'encoded-word' may appear.  In

   + An 'encoded-word' MUST NOT appear in any portion of an 'addr-spec'.

   + An 'encoded-word' MUST NOT appear within a 'quoted-string'.

   + An 'encoded-word' MUST NOT be used in a Received header field.

   + An 'encoded-word' MUST NOT be used in parameter of a MIME Content-Type
     or Content-Disposition field, or in any structured field body except
     within a 'comment' or 'phrase'.  (NOTE IN DRAFT: A means of encoding
     non-ASCII strings in MIME parameters has been proposed, and an
     internet-draft describing it is expected shortly.)

   The 'encoded-text' in an 'encoded-word' must be self-contained;
   'encoded-text' MUST NOT be continued from one 'encoded-word' to another.
   This implies that the 'encoded-text' portion of a "B" 'encoded-word'
   will be a multiple of 4 characters long; for a "Q" 'encoded-word', any
   "=" character that appears in the 'encoded-text' portion will be
   followed by two hexadecimal characters.

   Each 'encoded-word' MUST encode an integral number of octets.  The
   'encoded-text' in each 'encoded-word' must be well-formed according to
   the encoding specified; the 'encoded-text' may not be continued in the
   next 'encoded-word'.  (For example, "=?charset?Q?=?= =?charset?Q?AB?="
   would be illegal, because the two hex digits "AB" must follow the "=" in
   the same 'encoded-word'.)

   Each 'encoded-word' MUST represent an integral number of characters. A
   multi-octet character may not be split across adjacent 'encoded-word's.

   Only printable and white space character data should be encoded using
   this scheme.  However, since these encoding schemes allow the encoding
   of arbitrary octet values, mail readers that implement this decoding
   should also ensure that display of the decoded data on the recipient's
   terminal will not cause unwanted side-effects.

   Use of these methods to encode non-textual data (e.g., pictures or
   sounds) is not defined by this memo.  Use of 'encoded-word's to
   represent strings of purely ASCII characters is allowed, but
   discouraged.  In rare cases it may be necessary to encode ordinary text
   that looks like an 'encoded-word'.

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6. Support of 'encoded-word's by mail readers

   6.1. Recognition of 'encoded-word's in message headers

      A mail reader must parse the message and body part headers according
      to the rules in RFC 822 to correctly recognize 'encoded-word's.

      'encoded-word's are to be recognized as follows:

      (1) Any message or body part header field defined as '*text', or any
          user-defined header field, should be parsed as follows: Beginning
          at the start of the field-body and immediately following each
          occurrence of 'linear-white-space', each sequence of up to 75
          printable characters (not containing any 'linear-white-space')
          should be examined to see if it is an 'encoded-word' according to
          the syntax rules in section 2.  Any other sequence of printable
          characters should be treated as ordinary ASCII text.

      (2) Any header field not defined as '*text' should be parsed
          according to the syntax rules for that header field.  However,
          any 'word' that appears within a 'phrase' should be treated as an
          'encoded-word' if it meets the syntax rules in section 2.
          Otherwise it should be treated as an ordinary 'word'.

      (3) Within a 'comment', any sequence of up to 75 printable characters
          (not containing 'linear-white-space'), that meets the syntax
          rules in section 2, should be treated as an 'encoded-word'.
          Otherwise it should be treated as normal comment text.

      (4) A MIME-Version header field is NOT required to be present for
          'encoded-word's to be interpreted according to this
          specification.  One reason for this is that the mail reader is
          not expected to parse the entire message header before displaying
          lines that may contain 'encoded-word's.

   6.2. Display of 'encoded-word's

      Any 'encoded-word's so recognized are decoded, and if possible, the
      resulting unencoded text is displayed in the original character set.

      NOTE: Decoding and display of encoded-words occurs *after* a
      structured field body is parsed into tokens.  It is therefore
      possible to hide 'special' characters in encoded-words which, when
      displayed, will be indistinguishable from 'special' characters in the
      surrounding text.  For this and other reasons, it is NOT generally
      possible to translate a message header containing 'encoded-word's to
      an unencoded form which can be parsed by an RFC 822 mail reader.

      When displaying a particular header field that contains multiple
      'encoded-word's, any 'linear-white-space' that separates a pair of
      adjacent 'encoded-word's is ignored.  (This is to allow the use of

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      multiple 'encoded-word's to represent long strings of unencoded text,
      without having to separate 'encoded-word's where spaces occur in the
      unencoded text.)

      In the event other encodings are defined in the future, and the mail
      reader does not support the encoding used, it may either (a) display
      the 'encoded-word' as ordinary text, or (b) substitute an appropriate
      message indicating that the text could not be decoded.

      If the mail reader does not support the character set used, it may
      (a) display the 'encoded-word' as ordinary text (i.e., as it appears
      in the header), (b) make a "best effort" to display using such
      characters as are available, or (c) substitute an appropriate message
      indicating that the decoded text could not be displayed.

      If the character set being used employs code-switching techniques,
      display of the encoded text implicitly begins in "ASCII mode".  In
      addition, the mail reader must ensure that the output device is once
      again in "ASCII mode" after the 'encoded-word' is displayed.

   6.3. Mail reader handling of incorrectly formed 'encoded-word's

      It is possible that an 'encoded-word' that is legal according to the
      syntax defined in section 2, is incorrectly formed according to the
      rules for the encoding being used.   For example:

      (1) An 'encoded-word' which contains characters which are not legal
          for a particular encoding (for example, a "-" in the "B"
          encoding, or a SPACE or HTAB in either the "B" or "Q" encoding),
          is incorrectly formed.

      (2) Any 'encoded-word' which encodes a non-integral number of
          characters or octets is incorrectly formed.

      A mail reader need not attempt to display the text associated with an
      'encoded-word' that is incorrectly formed.  However, a mail reader
      MUST NOT prevent the display or handling of a message because an
      'encoded-word' is incorrectly formed.

7. Conformance

   A mail composing program claiming compliance with this specification
   MUST ensure that any string of non-white-space printable ASCII
   characters within a '*text' or '*ctext' that begins with "=?" and ends
   with "?=" be a valid 'encoded-word'.  ("begins" means: at the start of
   the field-body, immediately following 'linear-white-space', or
   immediately following a "(" for an 'encoded-word' within '*ctext';
   "ends" means: at the end of the field-body, immediately preceding
   'linear-white-space', or immediately preceding a ")" for an
   'encoded-word' within '*ctext'.)  In addition, any 'word' within a

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   'phrase' that begins with "=?" and ends with "?=" must be a valid

   A mail reading program claiming compliance with this specification must
   be able to distinguish 'encoded-word's from 'text', 'ctext', or 'word's,
   according to the rules in section 6, anytime they appear in appropriate
   places in message headers.  It must support both the "B" and "Q"
   encodings for any character set which it supports.  The program must be
   able to display the unencoded text if the character set is "US-ASCII".
   For the ISO-8859-* character sets, the mail reading program must at
   least be able to display the characters which are also in the ASCII set.

8. Examples

   The following are examples of message headers containing

   From: =?US-ASCII?Q?Keith_Moore?= <moore@cs.utk.edu>
   To: =?ISO-8859-1?Q?Keld_J=F8rn_Simonsen?= <keld@dkuug.dk>
   CC: =?ISO-8859-1?Q?Andr=E9?= Pirard <PIRARD@vm1.ulg.ac.be>
   Subject: =?ISO-8859-1?B?SWYgeW91IGNhbiByZWFkIHRoaXMgeW8=?=

      Note: In the first 'encoded-word' of the Subject field above, the
      last "=" at the end of the 'encoded-text' is necessary because each
      'encoded-word' must be self-contained (the "=" character completes a
      group of 4 base64 characters representing 2 octets).  An additional
      octet could have been encoded in the first 'encoded-word' (so that
      the encoded-word would contain an exact multiple of 3 encoded
      octets), except that the second 'encoded-word' uses a different
      'charset' than the first one.

   From: =?ISO-8859-1?Q?Olle_J=E4rnefors?= <ojarnef@admin.kth.se>
   To: ietf-822@dimacs.rutgers.edu, ojarnef@admin.kth.se
   Subject: Time for ISO 10646?

   To: Dave Crocker <dcrocker@mordor.stanford.edu>
   Cc: ietf-822@dimacs.rutgers.edu, paf@comsol.se
   From: =?ISO-8859-1?Q?Patrik_F=E4ltstr=F6m?= <paf@nada.kth.se>
   Subject: Re: RFC-HDR care and feeding

   From: Nathaniel Borenstein <nsb@thumper.bellcore.com>
   To: Greg Vaudreuil <gvaudre@NRI.Reston.VA.US>, Ned Freed
      <ned@innosoft.com>, Keith Moore <moore@cs.utk.edu>
   Subject: Test of new header generator
   MIME-Version: 1.0
   Content-type: text/plain; charset=ISO-8859-1

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   The following examples illustrate how text containing 'encoded-word's
   which appear in a structured field body.  The rules are slightly
   different for fields defined as '*text' because "(" and ")" are not
   recognized as 'comment' delimiters.  [Section 5, paragraph (1)].

   In each of the following examples, if the same sequence were to occur in
   a '*text' field, the "displayed as" form would NOT be treated as encoded
   words, but be identical to the "encoded form".  This is because each of
   the encoded-words in the following examples is adjacent to a "(" or ")"

   encoded form                                displayed as
   (=?ISO-8859-1?Q?a?=)                        (a)

   (=?ISO-8859-1?Q?a?= b)                      (a b)

           Within a 'comment', white space MUST appear between an
           'encoded-word' and surrounding text.  [Section 5,
           paragraph (2)].  However, white space is not needed between
           the initial "(" that begins the 'comment', and the

   (=?ISO-8859-1?Q?a?= =?ISO-8859-1?Q?b?=)     (ab)

           White space between adjacent 'encoded-word's is not

   (=?ISO-8859-1?Q?a?=  =?ISO-8859-1?Q?b?=)    (ab)

        Even multiple SPACEs between 'encoded-word's are ignored
        for the purpose of display.

   (=?ISO-8859-1?Q?a?=                         (ab)

           Any amount of linear-space-white between 'encoded-word's, even
           if it includes a CRLF followed by one or more SPACEs, is
           ignored for the purposes of display.

   (=?ISO-8859-1?Q?a_b?=)                      (a b)

           In order to cause a SPACE to be displayed within a portion
           of encoded text, the SPACE MUST be encoded as part of the

   (=?ISO-8859-1?Q?a?= =?ISO-8859-2?Q?_b?=)    (a b)

           In order to cause a SPACE to be displayed between two strings
           of encoded text, the SPACE MAY be encoded as part of one of the

K. Moore                                                       [Page 12]

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9. References

   [RFC 822] Crocker, D., "Standard for the Format of ARPA Internet Text
       Messages", RFC 822, UDEL, August 1982.
   [RFC CHARSET] N. Freed and J. Postel, "IANA Character Set Registration
       Procedures", Internet-Draft draft-freed-charset-reg-00.txt, 29 April
   [RFC MIME-CONF] N. Borenstein and N. Freed, "Multipurpose Internet Mail
       Extensions (MIME) Part Five: Conformance Criteria and Examples".
       Internet-Draft draft-ietf-822ext-mime-conf-05.txt, 13 March 1996.
   [RFC MIME-IMB] N. Borenstein and N. Freed, "Multipurpose Internet Mail
       Extensions (MIME) Part One: Format of Internet Message Bodies".
       Internet-Draft draft-ietf-822ext-mime-imb-06.txt, 13 March 1996.
   [RFC MIME-IMT] N. Borenstein and N. Freed, "Multipurpose Internet Mail
       Extensions (MIME) Part Two: Media Types". Internet-Draft draft-
       ietf-822ext-mime-imt-04.txt, 13 March 1996.
   [RFC MIME-REG] N. Freed, J. Klensin, and J. Postel.  "Multipurpose
       Internet Mail Extensions (MIME) Part Four: Registration Procedures",
       Internet-Draft draft-ietf-822ext-mime-reg-03.txt, 14 March 1996.

10. Security Considerations

   Security issues are not discussed in this memo.

11. Acknowledgements

   The author wishes to thank Nathaniel Borenstein, Issac Chan, Lutz
   Donnerhacke, Paul Eggert, Ned Freed, Andreas M. Kirchwitz, Olle
   Jarnefors, Mike Rosin, Yutaka Sato, Bart Schaefer, and Kazuhiko
   Yamamoto, for their helpful advice, insightful comments, and
   illuminating questions in response to earlier versions of this

12. Author's Address

   Keith Moore
   University of Tennessee
   107 Ayres Hall
   Knoxville TN 37996-1301

   EMail: moore@cs.utk.edu

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   Appendix - changes since RFC 1522 (in no particular order)

   + explicitly state that the MIME-Version is not requried to use

   + add explicit note that SPACEs and TABs are not allowed within
     'encoded-word's, explaining that an 'encoded-word' must look like an
     'atom' to an RFC822 parser.values, to be precise).

   + add examples from Olle Jarnefors (thanks!) which illustrate how
     encoded-words with adjacent linear-white-space are displayed.

   + explicitly list terms defined in RFC822 and referenced in this memo

   + fix transcription typos that caused one or two lines and a couple of
     characters to disappear in the resulting text, due to nroff quirks.

   + clarify that encoded-words are allowed in '*text' fields in both
     RFC822 headers and MIME body part headers, but NOT as parameter

   + clarify the requirement to switch back to ASCII within the encoded
     portion of an 'encoded-word', for any charset that uses code switching

   + add a note about 'encoded-word's being delimited by "(" and ")"
     within a comment, but not in a *text (how bizarre!).

   + fix the Andre Pirard example to get rid of the trailing "_" after
     the =E9.  (no longer needed post-1342).

   + clarification: an 'encoded-word' may appear immediately following
     the initial "(" or immediately before the final ")" that delimits a
     comment, not just adjacent to "(" and ")" *within* *ctext.

   + add a note to explain that a "B" 'encoded-word' will always have a
     multiple of 4 characters in the 'encoded-text' portion.

   + add note about the "=" in the examples

   + note that processing of 'encoded-word's occurs *after* parsing, and
     some of the implications thereof.

   + explicitly state that you can't expect to translate between
     1522 and either vanilla 822 or so-called "8-bit headers".

   + explicitly state that 'encoded-word's are not valid within a

K. Moore                                                       [Page 14]