Date and Timezone: draft text

Here's draft text to clarify that timezone is NOT recorded
in the formula work; comments?  I intend to put this in the section
on Date and Datetime subtypes.  This will (hopefully) resolve the issue,
as discussed in the last TC teleconference.

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The Date and Datetime subtypes (number of days since the
beginning of the epoch) do not include a mechanism for recording the
time zone.  Instead, these subtypes only presume that all
date or datetime values use the same unspecified time zone.
Document creators CAN use formulas to do time zone
translations using formulas, and CAN decide on a particular single time zone
such as UTC (Coordinated Universal Time) when developing a particular document.
Similarly, the Date and Datetime subtypes do not include a mechanism
for distinguishing the value of a leap second and the following second,
and presume that every day is exactly 24 hours long.

--- David A. Wheeler