rfc2822 April 2001

3.3. Date and Time Specification

   Date and time occur in several header fields.  This section specifies
   the syntax for a full date and time specification.  Though folding
   white space is permitted throughout the date-time specification, it
   is RECOMMENDED that a single space be used in each place that FWS
   appears (whether it is required or optional); some older
   implementations may not interpret other occurrences of folding white
   space correctly.

date-time       =       [ day-of-week "," ] date FWS time [CFWS]

day-of-week     =       ([FWS] day-name) / obs-day-of-week

day-name        =       "Mon" / "Tue" / "Wed" / "Thu" /
              "Fri" / "Sat" / "Sun"

date            =       day month year

year            =       4*DIGIT / obs-year

month           =       (FWS month-name FWS) / obs-month

month-name      =       "Jan" / "Feb" / "Mar" / "Apr" /
              "May" / "Jun" / "Jul" / "Aug" /
              "Sep" / "Oct" / "Nov" / "Dec"

day             =       ([FWS] 1*2DIGIT) / obs-day

time            =       time-of-day FWS zone

time-of-day     =       hour ":" minute [ ":" second ]

hour            =       2DIGIT / obs-hour

minute          =       2DIGIT / obs-minute

second          =       2DIGIT / obs-second

zone            =       (( "+" / "-" ) 4DIGIT) / obs-zone
   The day is the numeric day of the month.  The year is any numeric
   year 1900 or later.

   The time-of-day specifies the number of hours, minutes, and
   optionally seconds since midnight of the date indicated.

   The date and time-of-day SHOULD express local time.

   The zone specifies the offset from Coordinated Universal Time (UTC,
   formerly referred to as "Greenwich Mean Time") that the date and
   time-of-day represent.  The "+" or "-" indicates whether the
   time-of-day is ahead of (i.e., east of) or behind (i.e., west of)
   Universal Time.  The first two digits indicate the number of hours
   difference from Universal Time, and the last two digits indicate the
   number of minutes difference from Universal Time.  (Hence, +hhmm
   means +(hh * 60 + mm) minutes, and -hhmm means -(hh * 60 + mm)
   minutes).  The form "+0000" SHOULD be used to indicate a time zone at
   Universal Time.  Though "-0000" also indicates Universal Time, it is
   used to indicate that the time was generated on a system that may be
   in a local time zone other than Universal Time and therefore
   indicates that the date-time contains no information about the local
   time zone.

   A date-time specification MUST be semantically valid.  That is, the
   day-of-the-week (if included) MUST be the day implied by the date,
   the numeric day-of-month MUST be between 1 and the number of days
   allowed for the specified month (in the specified year), the
   time-of-day MUST be in the range 00:00:00 through 23:59:60 (the
   number of seconds allowing for a leap second; see [STD12]), and the
   zone MUST be within the range -9959 through +9959.