master
[build]: Add/update .gitignore files.
Reform terminology: hyphenation "flags" -> "mode".
[troff]: Trivially refactor.
[troff]: Trivially refactor for semantic clarity.
[troff]: Fix Savannah #68583.
[troff]: Slightly refactor.
[troff]: Tighten symbol visibility.
[libgroff,troff]: Refactor nonreturning functions.
[troff]: Fix Savannah #68555.
src/roff/troff/env.h: Fix cosmetic code nit.
[troff]: Cosmetically revise authorship notices.
src/roff/troff/input.cpp: Fix comment.
[troff]: Move external decl to header file. (1/2)
Rationalize header file inclusions.
[tmac,troff]: Fix Savannah #68345.
[troff]: Recast error diagnostic.
src/roff/troff/reg.cpp: Slightly refactor.
src/roff/troff/reg.h: Revise copyright notice.
[troff]: Unabbreviate member variables (1/2).
[troff]: Slightly expand internal API.
[doc,man]: Clarify warning category meanings.
Simplify handling of ".version" file.
[troff]: Rename `WARN_INVALID` enum constant.