See: Fn 3700H (query switch character)

Fn 3701H (set switch character)

These two functions are  Undocumented  and  Obsolete .

They were intended as part of a system that would enable DOS users to
select a character other than slash (/) as the lead character for command
options.  See the obsolete SWITCHAR= CONFIG.SYS command.

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DOS Fn 37H: Set or Query Switch Character