JdeBPIn contrast to : for comments which is an abuse of label syntax in command scripts, the REM command in Microsoft's/IBM's COMMAND and CMD is indeed exactly that, a bona fide command.
So it has the twist that REM /? is not actually a comment line. It's a request for the on-line help of the REM command.
It's more special cased in #TakeCommand than in #CMD, interestingly, in that redirections are not parsed.
https://jpsoft.com/help/rem.htm
https://learn.microsoft.com/en-gb/windows-server/administration/windows-commands/rem