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   'phrase' that begins with "=?" and ends with "?=" must be a valid   'encoded-word'.   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 'encoded-   word's:   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=?=    =?ISO-8859-2?B?dSB1bmRlcnN0YW5kIHRoZSBleGFtcGxlLg==?=      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 feedingMoore                       Standards Track                    [Page 11]RFC 2047               Message Header Extensions           November 1996   From: Nathaniel Borenstein <nsb@thumper.bellcore.com>         (=?iso-8859-8?b?7eXs+SDv4SDp7Oj08A==?=)   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   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 ")" character.   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           'encoded-word'.   (=?ISO-8859-1?Q?a?= =?ISO-8859-1?Q?b?=)     (ab)           White space between adjacent 'encoded-word's is not           displayed.   (=?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)       =?ISO-8859-1?Q?b?=)           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.Moore                       Standards Track                    [Page 12]RFC 2047               Message Header Extensions           November 1996   (=?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           'encoded-word'.   (=?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 'encoded-word's.9. References   [RFC 822] Crocker, D., "Standard for the Format of ARPA Internet Text       Messages", STD 11, RFC 822, UDEL, August 1982.   [RFC 2049] Borenstein, N., and N. Freed, "Multipurpose Internet Mail       Extensions (MIME) Part Five: Conformance Criteria and Examples",       RFC 2049, November 1996.   [RFC 2045] Borenstein, N., and N. Freed, "Multipurpose Internet Mail       Extensions (MIME) Part One: Format of Internet Message Bodies",       RFC 2045, November 1996.   [RFC 2046] Borenstein N., and N. Freed, "Multipurpose Internet Mail       Extensions (MIME) Part Two: Media Types", RFC 2046,       November 1996.   [RFC 2048] Freed, N., Klensin, J., and J. Postel, "Multipurpose       Internet Mail Extensions (MIME) Part Four: Registration       Procedures", RFC 2048, November 1996.Moore                       Standards Track                    [Page 13]RFC 2047               Message Header Extensions           November 199610. 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   specification.12. Author's Address   Keith Moore   University of Tennessee   107 Ayres Hall   Knoxville TN 37996-1301   EMail: moore@cs.utk.eduMoore                       Standards Track                    [Page 14]RFC 2047               Message Header Extensions           November 1996Appendix - changes since RFC 1522 (in no particular order)   + explicitly state that the MIME-Version is not requried to use     'encoded-word's.   + 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     values.   + clarify the requirement to switch back to ASCII within the encoded     portion of an 'encoded-word', for any charset that uses code switching     sequences.   + 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     'quoted-string'.Moore                       Standards Track                    [Page 15]