+{-# LANGUAGE
+ UnicodeSyntax
+ #-}
+-- |This module provides functions to parse and format HTTP\/1.1 date
+-- and time formats.
+--
+-- The HTTP\/1.1 specification (RFC 2616) says that HTTP\/1.1 clients
+-- and servers which parse the date value MUST accept all the
+-- following formats, though they MUST only generate the RFC 1123
+-- format for representing HTTP-date values in header fields:
+--
+-- > Sun, 06 Nov 1994 08:49:37 GMT ; RFC 822, updated by RFC 1123
+-- > Sunday, 06-Nov-94 08:49:37 GMT ; RFC 850, obsoleted by RFC 1036
+-- > Sun Nov 6 08:49:37 1994 ; ANSI C's asctime() format
+--
+-- It also says that all HTTP date\/time stamps MUST be represented in
+-- Greenwich Mean Time (GMT), without exception. For the purposes of
+-- HTTP, GMT is exactly equal to UTC (Coordinated Universal
+-- Time). This is indicated in the first two formats by the inclusion
+-- of @\"GMT\"@ as the three-letter abbreviation for time zone, and
+-- MUST be assumed when reading the asctime format.
+--
+-- > HTTP-date = rfc1123-date | rfc850-date | asctime-date
+-- > rfc1123-date = wkday "," SP date1 SP time SP "GMT"
+-- > rfc850-date = weekday "," SP date2 SP time SP "GMT"
+-- > asctime-date = wkday SP date3 SP time SP 4DIGIT
+-- > date1 = 2DIGIT SP month SP 4DIGIT
+-- > ; day month year (e.g., 02 Jun 1982)
+-- > date2 = 2DIGIT "-" month "-" 2DIGIT
+-- > ; day-month-year (e.g., 02-Jun-82)
+-- > date3 = month SP ( 2DIGIT | ( SP 1DIGIT ))
+-- > ; month day (e.g., Jun 2)
+-- > time = 2DIGIT ":" 2DIGIT ":" 2DIGIT
+-- > ; 00:00:00 - 23:59:59
+-- > wkday = "Mon" | "Tue" | "Wed"
+-- > | "Thu" | "Fri" | "Sat" | "Sun"
+-- > weekday = "Monday" | "Tuesday" | "Wednesday"
+-- > | "Thursday" | "Friday" | "Saturday" | "Sunday"
+-- > month = "Jan" | "Feb" | "Mar" | "Apr"
+-- > | "May" | "Jun" | "Jul" | "Aug"
+-- > | "Sep" | "Oct" | "Nov" | "Dec"