[bug #61055] [me] Explain how -me documents can use groff's unlimited number of environments

[Dave]

URL:
  <https://savannah.gnu.org/bugs/?61055>

                 Summary: [me] Explain how -me documents can use groff's
unlimited number of environments
                 Project: GNU troff
            Submitted by: barx
            Submitted on: Wed 18 Aug 2021 08:04:37 AM CDT
                Category: Macro - me
                Severity: 1 - Wish
              Item Group: Documentation
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: None

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Details:

In olden days, when the -me macro set was written, troff offered only three
environments (.ev request), numbered 0, 1, and 2.  In its implementation, the
-me macro set uses these historical environments internally for things such as
page headers and footers and footnotes.  This meant that in historical troff,
environments were unavailable to end users of -me.

Groff changed this situation by expanding the number of environments from
three to infinity.  The -me documentation was never updated to reflect this
new situation.

This might be OK.  A number of things that troff itself associates with an
environment (such as type size and line spacing), -me stores in registers,
which are always global across environments.  Many -me macros (such as the
various paragraph macros: .pp, .lp, .ip, etc.) set these attributes based on
the respective registers every time they're invoked.  So properties that are
per-environment in troff tend to be global under normal -me usage.  (See
http://lists.gnu.org/archive/html/groff/2012-03/msg00005.html for more about
this.)

Conversely, it might make sense to go ahead and document the expanded
environment functionality now available to -me users, even though it won't act
precisely as in generic troff.

----

If it is decided that the documentation should be so updated, new text would
need to explain the use of environments in -me, and how to avoid colliding
with -me's internal use of environments.  Additionally:

* "environments" would need to be added to the -Me Reference Manual's opening
paragraph telling what general troff knowledge the manual presumes
* the .ev and .evc requests should be added to the manual's index, which
includes, in addition to all the macros -me defines, "selected troff
requests... [that] can generally be used with impunity."

(This issue was tangentially mentioned in comment 6 of bug #55060.)




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