Local vs. UTC Dates and times

1/ Conversion from UTC to local time

Provide an option to display local dates and times using the UTC -> local
time DST conversion rule in effect at the instant specified in UTC instead
of what is in effect at the time of command execution. For those commands
and functions which accept the subcode U for UTC an alternate subcode L
(short for Legal) could be used with 100% backward compatibility.

2/ Conversion from local time to UTC

Provide an option to indicate how to process DST - use the DST state in
effect at the time of command execution (default, which ignores the state of
DST at the time instant specified) or to use its state at the specified
instant - the new option. Existing aliases and batch files would not have
the new option, thus would execute as before - 100% backward compatibility.