Hi!

I'm attaching a manual that reproduces this; in short:
  .Bl -tag -compact -offset 4n -width ".Sy \e\e , \ea , \eb , \et"
works, but
  .Bl -tag -offset 4n -width ".Sy [\& Ns Ar c Ns Sy *] , [\& Ns Ar c Ns Sy * Ns Ar len Ns Sy \&]"
doesn't.

Wherein "doesn't" is defined as "I think it's just taking the literal
width of the string", which means mandoc really struggles to set this:
-- >8 --
OOPPTTIIOONNSS
   SSEETT EEXXPPAANNSSIIOONN
     In all places where an arbitrary character is allowed, it can instead be
     one of the following escapes:
         \\\\, \\aa, \\bb, \\tt
         \\nn, \\vv, \\ff, \\rr         The backslash, bell, backspace, tab, line
                                feed, vertical tab, form feed, and carriage
                                return characters, respectively.
         \\_O[_O[_O]]               Octal byte of value.
         \\_c                     Literal _c, without considering any other
                                sequences.

     Additionally, the following expansions are recognised:

         _f--_t                                                           Inclusive
                                                                       range
                                                                       of all
                                                                       &c.

         [[::_c_l_a_s_s::]]                                                     Where
                                                                       _c_l_a_s_s
                                                                       may be
                                                                       any of
                                                                         aallnnuumm       alphanumeric
                                                                                     characters
                                                                         aallpphhaa       letters
                                                                         bbllaannkk       blanks
-- >8 --

This is on a fresh (like, 20 minutes old) CVS checkout,
and also affects 1.14.5-1 off Debian.

groff processes this fine in both [nt]roff modes.

Best,
наб