1 January 1970, 00:00 UTC.  Note that the count of seconds does not
include any leap seconds; seconds are counted as if each UTC day has
exactly 86400 seconds.  Tcl responds to leap seconds by speeding or
slowing its clock by a tiny fraction for some minutes until it is
back in sync with UTC; its data model does not represent minutes that
have 59 or 61 seconds.
.TP
\fI\-now\fR
Instead of \fItimeVal\fR a non-integer option \fI\-now\fR can be used as
replacement for today, which is simply interpolated to the runt-time as value
of \fBclock seconds\fR. For example:
.sp
\fBclock format -now -f %a; # current day of the week\fR
.sp
\fBclock add -now 1 month; # next month\fR
.TP
\fIunit\fR
One of the words, \fBseconds\fR, \fBminutes\fR, \fBhours\fR,
\fBdays\fR, \fBweekdays\fR, \fBweeks\fR, \fBmonths\fR, or \fByears\fR.
Used in conjunction with \fIcount\fR to identify an interval of time,
for example, \fI3 seconds\fR or \fI1 year\fR.
.SS "OPTIONS"
.TP

string of the same meaning in the locale, to indicate whether \fB%Y\fR refers
to years before or after Year 1 of the Common Era.  On input, accepts
the string \fBB.C.E.\fR, \fBB.C.\fR, \fBC.E.\fR, \fBA.D.\fR, or the
abbreviation appropriate to the current locale, and uses it to fix
whether \fB%Y\fR refers to years before or after Year 1 of the
Common Era.
.TP
\fB%Es\fR
This affects similar to \fB%s\fR, but in opposition to \fB%s\fR it parses
or formats local seconds (not the posix seconds).
Because \fB%s\fR has the same precedence as \fB%s\fR (uniquely determines 
a point in time), it overrides all other input formats.
.TP
\fB%Ex\fR
On output, produces a locale-dependent representation of the date
in the locale's alternative calendar.  On input, matches
whatever \fB%Ex\fR produces.  The locale's alternative calendar need not
be the Gregorian calendar.
.TP
\fB%EX\fR

that \fB%Y\fR does not yield a year appropriate for use with the ISO8601
week number \fB%V\fR; programs should use \fB%G\fR for that purpose.
.TP
\fB%z\fR
On output, produces the current time zone, expressed in hours and
minutes east (+hhmm) or west (\-hhmm) of Greenwich. On input, accepts a
time zone specifier (see \fBTIME ZONES\fR below) that will be used to
determine the time zone.
determine the time zone (this token is optionally applicable on input, 
so the value is not mandatory and can be missing in input).
.TP
\fB%Z\fR
On output, produces the current time zone's name, possibly
translated to the given locale. On input, accepts a time zone
specifier (see \fBTIME ZONES\fR below) that will be used to determine the
time zone (token is also like \fB%z\fR optionally applicable on input).
time zone. This option should, in general, be used on input only when
This option should, in general, be used on input only when
parsing RFC822 dates. Other uses are fraught with ambiguity; for
instance, the string \fBBST\fR may represent British Summer Time or
Brazilian Standard Time. It is recommended that date/time strings for
use by computers use numeric time zones instead.
.TP
\fB%%\fR
On output, produces a literal

Using that time as the base, day-of-week specifications are added.
Next, relative specifications are used.  If a date or day is
specified, and no absolute or relative time is given, midnight is
used.  Finally, a correction is applied so that the correct hour of
the day is produced after allowing for daylight savings time
differences and the correct date is given when going from the end
of a long month to a short month.
.PP
The precedence of the applying of single tokens resp. which sequence will be
used by calculating of the time is complex, e. g. heavily dependent on the
precision of type of the token.
.sp
In example below the second date-string contains "next January", therefore
it results in next year but in January. And third date-string besides "January"
contains also additionally "Fri", so it results in the nearest Friday.
Thus both win before "385 days" resp. make it more precise, because of higher 
precision of this token types.
.CS
% clock format [clock scan "5 years 18 months 385 days" -base 0 -gmt 1] -gmt 1
Thu Jul 21 00:00:00 GMT 1977
% clock format [clock scan "5 years 18 months 385 days next January" -base 0 -gmt 1] -gmt 1
Sat Jan 21 00:00:00 GMT 1978
% clock format [clock scan "5 years 18 months 385 days next January Fri" -base 0 -gmt 1] -gmt 1
Fri Jan 27 00:00:00 GMT 1978
.CE
.SH "SEE ALSO"
msgcat(n)
.SH KEYWORDS
clock, date, time
.SH "COPYRIGHT"
Copyright (c) 2004 Kevin B. Kenny <kennykb@acm.org>. All rights reserved.
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