Revert "[S32::Temporal] Expand valid ISO 8601 formats."

ISO 8601 is a good thing, but that does not mean *all* of it is
a good thing. Specifiacally, allowing week specifications in the
DateTime core will make the logic even more complicated than it
already is, with extremely little benefit.

This reverts commit 97c5bc4.

S32-setting-library/Temporal.pod

@@ -101,38 +101,21 @@ from UTC. The default time zone is C<0> (i.e., UTC).
 The system's local time zone is available as C<$*TZ>.
 
 A shorter way to send in date and time information is to provide a
-single string with a valid ISO 8601 date and time. The example from above
+single string with a full ISO 8601 date and time. The example from above
 would then be
 
     my $moonlanding = DateTime.new( '1969-07-16T20:17:00Z' ); # UTC time
 
-The general form is C<[date]T[time][offset]>, with C<[date]> and C<[time]>
-required, and C<[offset]> optional. All fields require leading zeros to pad to
-the correct number of digits.
-
-The C<[date]> portion may be given in any of the forms C<YYYY-MM-DD>,
-C<YYYY-MM>, C<YYYY-Www>, C<YYYY-Www-D>, or C<YYYY-DDD>. Omitted values are set
-to their defaults as listed in the named arguments form above. Note that
-C<DateTime> does not support year numbers requiring more than four digits with
-this constructor.
-
-The C<[time]> portion may be given in any of C<hh:mm:ss>, C<hh:mm>, or
-C<hh>. Omitted values are set to their defaults.
-
-Fractional values are only kept for the seconds field. Fractions in the hour and
-minute fields are converted to integer combinations of it and more granular
-fields before storing the values. Fractions may only occurs in the
-smallest-occuring time unit.
-
-The C<[offset]> portion may be any of C<Z>, C<±hh:mm>, C<±hhmm>, or C<±hh>. C<Z>
-is considered a shorthand for C<+0000>, UTC time. An offset, if provided, is set
-as the timezone of the C<DateTime> object. If you leave out the offset in the
-string, you can use the C<:timezone> named argument alongside it. If no timezone
-information is given, the object is set to UTC by default.
-
-The date and time forms may optionally omit the separators, either the hyphens
-in the date, or the colons in the time. The notable exception is the C<YYYY-MM>
-form of date, which must retain its hyphen.
+The general form is C<[date]T[time][offset]>, with C<[date]> given as
+C<YYYY-MM-DD> and C<[time]> given as C<hh:mm:ss>. The final C<Z> is a short
+form for C<+0000>, meaning UTC. (Note that while this form of C<new>
+accepts all of C<+0000>, C<-0000>, and C<Z>, the default formatter for
+C<DateTime> always expresses UTC as C<Z>.) The general notation for the
+C<[offset]> is C<+hhmm> or C<-hhmm>. The time zone of the new object is
+assumed to be a static offset equal to the C<[offset]>. The C<[offset]> is
+optional; if omitted, a C<:timezone> argument is permitted; if this too is
+omitted, UTC is assumed. Finally, the constructor also accepts a
+C<:formatter> argument.
 
 With all the above constructors, if you attempt to pass in values that
 are outside of the ranges specified in the list above, you'll get an
@@ -251,9 +234,6 @@ Days, Months and days of week are 1-based.
     Date.new(2010, 12, 24).truncated-to(week);
     Date.new(2010, 12, 24).delta(10, weeks);
 
-All ISO-8601 date formats are acceptable, with any time portion ignored
-(possibly with a warning.)
-
 The constructors die with a helpful error message if month or day are out of
 range.