rfc2047.txt

一个基于html的【pop客户端程序

   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?= <[e-mail]>
   To: =?ISO-8859-1?Q?Keld_J=F8rn_Simonsen?= <[e-mail]>
   CC: =?ISO-8859-1?Q?Andr=E9?= Pirard <[e-mail]>
   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?= <[e-mail]>
   To: [e-mail], [e-mail]
   Subject: Time for ISO 10646?

   To: Dave Crocker <[e-mail]>
   Cc: [e-mail], [e-mail]
   From: =?ISO-8859-1?Q?Patrik_F=E4ltstr=F6m?= <[e-mail]>
   Subject: Re: RFC-HDR care and feeding





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RFC 2047               Message Header Extensions           November 1996


   From: Nathaniel Borenstein <[e-mail]>
         (=?iso-8859-8?b?7eXs+SDv4SDp7Oj08A==?=)
   To: Greg Vaudreuil <[e-mail]>, Ned Freed
      <[e-mail]>, Keith Moore <[e-mail]>
   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.



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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.



















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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
   specification.

12. Author's Address

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

   EMail: [e-mail]






























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RFC 2047               Message Header Extensions           November 1996


Appendix - 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'.



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