11 
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Date
例:
              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

Content-Type
Content-Type = "Content-Type"  ":"  media-type
media-type = type "/" subtype *( ";" parameter )
例:
              text/html; charset=ISO-8859-4