hixie: Change what was non-normatively implied to be proleptic UTC to explicitly and normatively be proleptic UT1. (whatwg r5913)

hixie: Change what was non-normatively implied to be proleptic UTC to
explicitly and normatively be proleptic UT1. (whatwg r5913)

http://dev.w3.org/cvsweb/html5/spec/Overview.html?r1=1.4752&r2=1.4753&f=h
http://html5.org/tools/web-apps-tracker?from=5912&to=5913

===================================================================
RCS file: /sources/public/html5/spec/Overview.html,v
retrieving revision 1.4752
retrieving revision 1.4753
diff -u -d -r1.4752 -r1.4753
--- Overview.html 25 Feb 2011 07:13:13 -0000 1.4752
+++ Overview.html 25 Feb 2011 07:53:04 -0000 1.4753
@@ -4479,16 +4479,23 @@
   </ol><p class="note">This format allows for time-zone offsets from -23:59
   to +23:59. In practice, however, the range of offsets of actual time
   zones is -12:00 to +14:00, and the minutes component of offsets of
-  actual time zones is always either 00, 30, or 45.<div class="example">
+  actual time zones is always either 00, 30, or 45.<p>Times in dates before the formation of UTC in the mid twentieth
+  century must be expressed and interpreted in terms of UT1
+  (contemporary Earth solar time at the 0&deg; longitude), not UTC
+  (the approximation of UT1 that ticks in SI seconds). Time before the
+  formation of time zones must be expressed and interpeted as UT1
+  times with explicit time zones that approximate the contemporary
+  difference between the appropriate local time and the time observed
+  at the location of Greenwich, London.<div class="example">
 
    <p>The following are some examples of dates written as <a href="#valid-global-date-and-time-string" title="valid global date and time string">valid global date and
    time strings</a>.</p>
 
    <dl><dt>"<code>0037-12-13T00:00Z</code>"</dt>
 
-    <dd>Midnight UTC on the birthday of Nero (the Roman Emperor). See
-    below for further discussion on which date this actually
-    corresponds to.</dd>
+    <dd>Midnight in areas using London time on the birthday of Nero
+    (the Roman Emperor). See below for further discussion on which
+    date this actually corresponds to.</dd>
 
     <dt>"<code>1979-10-14T12:00:00.001-04:00</code>"</dt>
 
@@ -4509,21 +4516,27 @@
     zero-padded. The date "37-12-13" would not be a valid date.</li>
 
     <li>To unambiguously identify a moment in time prior to the
-    introduction of the Gregorian calendar, the date has to be first
-    converted to the Gregorian calendar from the calendar in use at
-    the time (e.g. from the Julian calendar). The date of Nero's birth
-    is the 15th of December 37, in the Julian Calendar, which is the
-    13th of December 37 in the proleptic Gregorian Calendar.</li> <!--
-    This might not be true. I can't find a reference that gives his
-    birthday with an explicit statement about the calendar being
-    used. However, it seems unlikely that it would be given in the
-    Gregorian calendar, so I assume sites use the Julian one. -->
+    introduction of the Gregorian calendar (insofar as moments in time
+    before the formation of UTC can be unambiguously identified), the
+    date has to be first converted to the Gregorian calendar from the
+    calendar in use at the time (e.g. from the Julian calendar). The
+    date of Nero's birth is the 15th of December 37, in the Julian
+    Calendar, which is the 13th of December 37 in the proleptic
+    Gregorian Calendar.</li> <!-- This might not be true. I can't find
+    a reference that gives his birthday with an explicit statement
+    about the calendar being used. However, it seems unlikely that it
+    would be given in the Gregorian calendar, so I assume sites use
+    the Julian one. -->
 
     <li>The time and time-zone offset components are not optional.</li>
 
     <li>Dates before the year one can't be represented as a datetime
     in this version of HTML.</li>
 
+    <li>Times of specific events in ancient times are, at best,
+    approximations, since time was not well coordinated or measured
+    until relatively recent decades.</li>
+
     <li>Time-zone offsets differ based on daylight savings time.</li>
 
    </ul></div><div class="impl">

Received on Friday, 25 February 2011 07:55:15 UTC