[Remind-Fans] Access to the FROM/SCANFROM, UNTIL/THROUGH, and AT/DURATION in a reminder?

[Tim Chase]

Is there any way for an expression or substitution to access the
values supplied in a FROM/SCANFROM and UNTIL/THROUGH (or the times
provided by the AT & DURATION clauses, or the TAG value)?

I can currently do something like

  REM Mon Tue Wed Thu Fri \
    FROM Dec 21 2019 \
    UNTIL Jan 5 2020 \
    MSG %"Kids on school break%"%
  REM Jan 16 2020 \
    AT 10:00 \
    DURATION 1:30 \
    MSG %"Dr. appointment%"%

which puts the MSG on the appropriate weekdays, but was hoping for
some sort of way to reference those dates, something like the
imaginary syntax

  # ...
  MSF %"Kids on school break from [$From] through [$Until] %"%
  # ...
  MSF %"Dr. appointment from [time($At)] to [$At + $Duration]%"%

such that

  $ rem 2019-12-23

(right in the middle of that range) would produce output something
like

  Reminders for Monday, 23rd December, 2019:
  Kids on school break from 2019-12-21 through 2020-01-05
  Dr. appointment from 10:00am to 11:30am

The only way I've been able to come up with a DRY(ish) solution is
still pretty verbose/ugly, something like

  SET WinterBreak2019Start date(2019,12,21)
  SET WinterBreak2019End   date(2020,1,5)
  REM Mon Tue Wed Thu Fri \
    FROM [WinterBreak2019Start] \
    UNTIL [WinterBreak2019End] \
    MSF %"Kids on school break [WinterBreak2019Start] through [WinterBreak2019End]%"%

which quickly becomes a royal pain.

Is this some existing functionality I've missed?  Or if it doesn't
exist, would it be a worthwhile sort of addition to propose for
consideration?

Thanks!

-tim