rfc2822 April 2001

4.3. Obsolete Date and Time

   The syntax for the obsolete date format allows a 2 digit year in the
   date field and allows for a list of alphabetic time zone
   specifications that were used in earlier versions of this standard.
   It also permits comments and folding white space between many of the
   tokens.

obs-day-of-week =       [CFWS] day-name [CFWS]

obs-year        =       [CFWS] 2*DIGIT [CFWS]

obs-month       =       CFWS month-name CFWS

obs-day         =       [CFWS] 1*2DIGIT [CFWS]

obs-hour        =       [CFWS] 2DIGIT [CFWS]

obs-minute      =       [CFWS] 2DIGIT [CFWS]

obs-second      =       [CFWS] 2DIGIT [CFWS]

obs-zone        =       "UT" / "GMT" /          ; Universal Time
                                      ; North American UT
                                      ; offsets
              "EST" / "EDT" /         ; Eastern:  - 5/ - 4
              "CST" / "CDT" /         ; Central:  - 6/ - 5
              "MST" / "MDT" /         ; Mountain: - 7/ - 6
              "PST" / "PDT" /         ; Pacific:  - 8/ - 7

              %d65-73 /               ; Military zones - "A"
              %d75-90 /               ; through "I" and "K"
              %d97-105 /              ; through "Z", both
              %d107-122               ; upper and lower case

   Where a two or three digit year occurs in a date, the year is to be
   interpreted as follows: If a two digit year is encountered whose
   value is between 00 and 49, the year is interpreted by adding 2000,
   ending up with a value between 2000 and 2049.  If a two digit year is
   encountered with a value between 50 and 99, or any three digit year
   is encountered, the year is interpreted by adding 1900.

   In the obsolete time zone, "UT" and "GMT" are indications of
   "Universal Time" and "Greenwich Mean Time" respectively and are both
   semantically identical to "+0000".

   The remaining three character zones are the US time zones.  The first
   letter, "E", "C", "M", or "P" stands for "Eastern", "Central",
   "Mountain" and "Pacific".  The second letter is either "S" for
   "Standard" time, or "D" for "Daylight" (or summer) time.  Their
   interpretations are as follows:

   EDT is semantically equivalent to -0400
   EST is semantically equivalent to -0500
   CDT is semantically equivalent to -0500
   CST is semantically equivalent to -0600
   MDT is semantically equivalent to -0600
   MST is semantically equivalent to -0700
   PDT is semantically equivalent to -0700
   PST is semantically equivalent to -0800

   The 1 character military time zones were defined in a non-standard
   way in [RFC822] and are therefore unpredictable in their meaning.
   The original definitions of the military zones "A" through "I" are
   equivalent to "+0100" through "+0900" respectively; "K", "L", and "M"
   are equivalent to  "+1000", "+1100", and "+1200" respectively; "N"
   through "Y" are equivalent to "-0100" through "-1200" respectively;
   and "Z" is equivalent to "+0000".  However, because of the error in
   [RFC822], they SHOULD all be considered equivalent to "-0000" unless
   there is out-of-band information confirming their meaning.
   Other multi-character (usually between 3 and 5) alphabetic time zones
   have been used in Internet messages.  Any such time zone whose
   meaning is not known SHOULD be considered equivalent to "-0000"
   unless there is out-of-band information confirming their meaning.