Apologies. enter (send) before typing.
on FreeBSD 13.1
fc [delimchar [padchar]] Define a delimiting and a padding
character for fields. Currently unsupported.
Also, fc is not recognised in mdoc as far as I can tell. A different
mechanism might be needed no matter what. in which case, dropping
use of fc and retaining man might work, but that said, this comment
from the man 7 man on OSX:
DESCRIPTION
The man language was the standard formatting language for AT&T
UNIX manual pages from 1979 to 1989. Do not use it to write
new manual pages: it is a purely presentational language and
lacks support for semantic markup. Use the mdoc(7) language,
instead.
-G