[bug #68597] doc/ms.ms.in: document does not render correctly

Follow-up Comment #9, bug #68597 (group groff):

[comment #7 comment #7:]
> You were right. A stray s.tmac had somehow found its way into the root of my
> home dircetory and which I had completely forgotten about, so you may close
> this as invalid. Still, I wonder why groff doesn't always look first in
> ${prefix}//share/groff/current/tmac

It's not straightforward for me to trace the history of this arrangement back
before 2014, when Bertrand ported _groff_'s build system to Automake.

But here's how the macro ("tmac") search path is constructed.


$ nl -ba Makefile.am | sed -n 142,161p
   142  # 'tmacdir' says where to install macros.
   143  tmacdir=$(datasubdir)/tmac
   144
   145  # 'systemtmacdir' says where to install platform-dependent macros.
   146  systemtmacdir=$(libprogramdir)/site-tmac
   147
   148  # 'localtmacdir' says where local files will be installed.
   149  localtmacdir=$(dataprogramdir)/site-tmac
   150
   151  # 'appdefdir' says where to install the application defaults file for
   152  # gxditview.
   153
   154  # glilypond_dir
   155  # gpinyin_dir
   156
   157  # 'tmacpath' says where to look for macro files.  The current
directory
   158  # is prepended at run time in unsafe mode only; the user's home
   159  # directory is always added.  "troffrc" and "troffrc-end" (and
"eqnrc")
   160  # are sought neither in the current nor in the home directory.
   161  tmacpath=$(systemtmacdir)$(RT_SEP)$(localtmacdir)$(RT_SEP)$(tmacdir)


Our _troff_(1) man page says a bit more:


     GROFF_TMAC_PATH
            A list of directories in which to search for macro files.
            troff will scan directories given as arguments to any
            specified -M options before these, then the current
            directory (only if in unsafe mode), the user’s home
            directory, a site‐specific directory (/home/branden/
            groff-HEAD/share/groff/site-tmac), and a standard location
            (/home/branden/groff-HEAD/share/groff/1.25.0/tmac) after
            them.


(These exact paths correspond, as you may guess, to my crazily bleeding-edge
working copy.  Yours will differ.)

_Why_ is the search path organized the way it is?  To be sure, we must ask
former _groff_ maintainers.

But my surmise is for user convenience in overriding or replacing system macro
files, by analogy to the long-standing Unix tradition of organizing the
command search path.

Here's a pattern you'll often see there.


PATH="$HOME"/bin:/usr/local/bin:/usr/bin:/bin


(In days of yore, "/usr" tended to be stored on a large disk drive distinct
from the smaller "boot" disk housing the root partition used to bring up the
system.  Among other frustrations, _fsck_(8) took forever in early days--to
say nothing of pre-_fsck_ days when you'd have to use inscrutable
Thompsonesque tools like _dcheck_ and _clri_.  System downtime was minimized
for administrators--and sometimes consequently users--by getting the "base"
system up and potentially into a limited multiuser environment ASAP after a
crash.  Multiple operators--or the same operator using multiple
terminals--could sign in and then run _fsck_ concurrently by hand on multiple
volumes that needed _fsck_ing.)

On some System V-ish systems, you might have found "/opt/bin" immediately
before or after "/usr/local/bin".

I suspect similar reasoning was applied here.  Observe the sequencing:

* `-M` macro directory arguments specified on the command line
* "." (unsafe mode only): whatever's sitting "right here" relative to the
document
* $HOME: user's customized macro package extensions or replacements
* /usr/share/groff/site-tmac: site-local macro package extensions or
replacements
* /usr/share/groff/1.25.0/tmac: stock macro packages as shipped by GNU

One can observe a pattern of the more specific preceding the more general.


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