commit 2a22ee31ebdaeab02a58825b3c4450c7bb70beee
Author: G. Branden Robinson <g.branden.robinson@gmail.com>
Date:   Fri Aug 4 09:28:55 2023 -0500

    [man]: Deprecate `SB` macro.

    It is a SunOS 4.0 (1988) extension that in most contexts, does nothing
    you can't achieve with `SM` and `B` together (in either order).

    Study of the SunOS 4 man page corpus suggests a reason for its
    introduction of this macro: use of `SB` immediately after `TP` was
    common (610 out of 2,111 occurrences).  The problem with `TP` and the
    mechanism suggested above is that input traps in troff normally ignore
    the `\c` escape sequence, the use of which would be necessary to get the
    desired effect.  In groff since 1.22.4, the man(7) `TP` macro uses GNU
    troff's `itc` request, which _does_ respect `\c`.  (mandoc(1) behaves
    compatibly with groff man >= 1.22.4.)  Solaris 11 switched to groff as
    its troff implementation, so there is no reason for newly written or
    currently maintained man pages to employ `SB`.

    * tmac/an.tmac (SB): Throw deprecation warning.

    * tmac/groff_man.7.man.in (Description): Move macro from table to
      deprecation list.

      (Font style macros): Move description from here...
      (Deprecated features): ...to here.

      (Portability): Drop mention, since we don't encourage people to
      use it at all.

    Fixes <https://savannah.gnu.org/bugs/?64515>.