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Created attachment 1534 [details] Fix some confusions involving Universal Time and old time stamps. The HTML5 spec requires UT1 for pre-UTC time stamps, but in practice UT2 was the basis of civil timekeeping just before UTC was inaugurated, and UT0 is a better choice than UT1 if you go back far enough. But the main point is that the HTML standard shouldn't try to impose a "must" time standard here (UT1 vs UT2 vs whatever) when this doesn't correspond to common practice. Instead, the standard should simply call out Universal Time as a general term. A proposed patch is attached. Some other minor changes for this edit: * Change a couple of "must"s to "should"s when "must" is too strong. * Mention that UT is mean solar time, not solar time. * Don't require actual observations at Greenwich for old time stamps -- if you go back far enough, nobody was at Greenwich to observe anything. My source for UT2 being the basis of civil timekeeping just before UTC is the following email from Steve Allen of UCO/Lick Observatory: http://mm.icann.org/pipermail/tz/2014-November/021867.html He cites the Bulletin Horaire of the Bureau International de l'Heure, March-April 1960, which is archived here: https://plus.google.com/photos/112320138481375234766/albums/6078225731350227361
HTML5.1 Bugzilla Bug Triage: Fixed, The term "must" is necessary in order to get a consistent conversion across browsers with a consistent format. I see no need to change this. However, I have added "mean" solar time and clarified that the Greenwich is the location of Greenwich not specifically the city but the "location". https://github.com/w3c/html/pull/275 If this resolution is not satisfactory, please copy the relevant bug details/proposal into a new issue at the W3C HTML5 Issue tracker: https://github.com/w3c/html/issues/new where it will be re-triaged. Thanks!