<META HTTP-EQUIV="EXPIRES" CONTENT="Mon, 22 Jul 2002 11:12:01 GMT">

The date and time after which the document should be considered expired. An illegal EXPIRES date, e.g. "0", is interpreted as "now". Setting EXPIRES to 0 may thus be used to force a modification check at each visit.
Web robots may delete expired documents from a search engine, or schedule a revisit.

HTTP 1.1 (RFC 2068) specifies that all HTTP date/time stamps MUST be generated in Greenwich Mean Time (GMT) and in RFC 1123 format.
RFC 1123 format = wkday "," SP date SP time SP "GMT"

wkday = (Mon, Tue, Wed, Thu, Fri, Sat, Sun)
date = 2DIGIT SP month SP 4DIGIT ; day month year (e.g., 02 Jun 1982)
time = 2DIGIT ":" 2DIGIT ":" 2DIGIT ; 00:00:00 - 23:59:59
month = (Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec)

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