       convertclock dateString ?GMT|{}? ?baseClock?
              Convert  dateString  to an integer clock value (see
              getclock).  This command can parse and convert vir-
              tually  any standard date and/or time string, which
              can include standard time zone mnemonics.  If  only
              a  time  is specified, the current date is assumed.
              If  the  string  does  not  contain  a  time   zone
              mnemonic,  the  local  time zone is assumed, unless
              the GMT argument is specified, in  which  case  the
              clock  value is calculated assuming that the speci-
              fied time is relative to Greenwich Mean Time.

              If baseClock is specified,  it  should  contain  an
              integer  clock  value.  Only the date in this value
              is used, not the time.  This is useful  for  deter-
              mining  the  time  on a specific day or doing other
              date-relative conversions.

              The character string consists of zero or more spec-
              ifications of the following form:

              time  -  A  time  of  day,  which  is  of  the form
              hh[:mm[:ss]] [meridian] [zone] or  hhmm  [meridian]
              [zone].   If no meridian is specified, hh is inter-
              preted on a 24-hour clock.

              date - A specific month and day with optional year.
              The  acceptable formats are mm/dd[/yy], yyyy/mm/dd,
              monthname dd[, yy], dd monthname [yy], and day,  dd
              monthname  yy.   The  default  year  is the current
              year.  If the year is less then 100, then  1900  is
              added to it.

              relative  time  -  A  specification relative to the
              current time.  The format is number  unit;  accept-
              able  units  are year, fortnight, month, week, day,
              hour, minute (or min), and second  (or  sec).   The
              unit  can  be specified as a singular or plural, as
              in 3 weeks.  These modifiers may also be specified:
              tomorrow,  yesterday, today, now, last, this, next,
              ago.

              The actual date is calculated according to the fol-
              lowing steps.  First, any absolute date and/or time
              is processed and converted.  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 pro-
              duced after allowing for daylight savings time dif-
              ferences.

              convertclock  ignores  case when parsing all words.
              The names of the months and days of the week can be
              abbreviated  to  their  first  three  letters, with
              optional trailing period.  Periods are  ignored  in
              any timezone or meridian values.

              Note  that convertclock will convert symbolic time-
              zone names, but  these  are  not  standardized  and
              there  are  conflicts  with  various  parts  of the
              world.  Use GMT when trying to produce  a  portable
              time  that  can then be converted back to a numeric
              value.

              The only dates in the range 1902 and  2037  may  be
              converted.  Some examples are:

                  convertclock "14 Feb 92"
                  convertclock "Feb 14, 1992 12:20 PM PST"
                  convertclock "12:20 PM Feb 14, 1992"

              This command is provided by Extended Tcl.
