The forthcoming groff 1.24 has a new diagnostic that detects ill-formed
numeric expressions. It has found one here.
I'm not positive what was intended here, but it may have been an attempt
to force interpretation of the first macro argument as a number. This
change employs a more idiomatic (but still old-school) technique.
The salient fact is that, in *roff, you can't affix a scaling unit after
a closing parenthesis (or another scaling unit).
In GNU troff the `\B` escape sequence, an extension, permits the testing
of putative numeric expressions for validity.
troff:./doc/Guidebook.mn:268: warning: expected end of line or an
auto-increment argument in register definition request; got character
'v'
See <https://savannah.gnu.org/bugs/?64240>.
cbff67b0d6