[docs]: Reduce use of term "entity".

Doug McIlroy noted this vague term, which groff employs for multiple
purposes.  Eliminate its application to input processing.  There is now
no longer such a thing as an "entity" in the groff language.

* doc/groff.texi (Character Translations): Do it.  Also clarify
  "nothing" as "the dummy character".

  (Using Symbols): Do it.  Also recast explanation of difference between
  characters and glyphs.  Explicitly state that spaces aren't glyphs.
  Document that `rchar` request can't remove definitions supplied by
  font description files.

  (Ligatures and Kerning): Speak of "special characters", not
  "entities".

  (Other Differences): Recast discussion of character-to-glyph
  transformation.  Stop qualifying characters as "input".  Recast
  discussion of example.

* font/devutf8/NOTES: Revise use of terminology.  Perform a Kemper
  notectomy.  Wrap long lines.

* man/groff.7.man (Request short reference) <char>: Speak of a "special
  character", not an "entity".

  <rchar>: Document that request can't remove definitions supplied by
  font description files.

* man/groff_diff.7.man (Implementation differences): Sync with our
  Texinfo manual.

The use of "entity" to describe how a glyph gets mapped back to a
character (sequence) for the HTML and terminal output devices is
retained.  That usage is restricted to discussion of output drivers
(code comments and function names notwithstanding).

2 files changed, 55 insertions, 40 deletions

diff --git a/man/groff.7.man b/man/groff.7.man
index 07944567d..af1ebbbb2 100644
--- a/man/groff.7.man
+++ b/man/groff.7.man
@@ -1254,8 +1254,11 @@ containing them is surrounded by parentheses.
 .\" ====================================================================
 .
 .\" BEGIN Keep (roughly) parallel with groff.texi node "Identifiers".
-An identifier is a label for an object of syntactical importance:
-a register,
+An
+.I identifier
+labels a GNU
+.I troff \" GNU
+datum such as a register,
 name
 (macro,
 string,
@@ -2581,7 +2584,7 @@ Reset no-break control character to
 .REQ .c2 "o"
 Recognize ordinary character
 .I o
-as the no-break control character.
+as no-break control character.
 .
 .TPx
 .REQ .cc
@@ -2646,7 +2649,7 @@ by moving its location to
 .
 .TPx
 .REQ .char "c contents"
-Define entity
+Define ordinary or special character
 .I c
 as
 .IR contents .
@@ -3800,11 +3803,16 @@ Change post-vertical line spacing according to
 .scaleindicator p ).
 .
 .TPx
-.REQ .rchar "c1 c2 \fR\&.\|.\|.\&\fP"
-Remove the definitions of entities
+.REQ .rchar "c1 c2 \fR.\|.\|.\&\fP"
+Remove definition of each ordinary or special character
 .IR c1 ,
 .IR c2 ,
-\&.\|.\|.\&
+\&.\|.\|.\& defined by a
+.request .char ,
+.request .fchar ,
+or
+.request .schar
+request.
 .
 .TPx
 .REQ .rd "prompt"
diff --git a/man/groff_diff.7.man b/man/groff_diff.7.man
index e1a17c598..56770f0ef 100644
--- a/man/groff_diff.7.man
+++ b/man/groff_diff.7.man
@@ -5453,45 +5453,48 @@ each rounded down to the nearest multiple of\~12.
 .
 .
 .P
-In
-.IR groff ,
-there is a fundamental difference between unformatted input
-characters, and formatted output characters (glyphs).
+In GNU
+.I troff \" GNU
+there is a fundamental difference between (unformatted) characters and
+(formatted) glyphs.
 .
-Everything that affects how a glyph is output is stored with the glyph;
-once a glyph has been constructed,
+Everything that affects how a glyph is output is stored with the glyph
+node;
+once a glyph node has been constructed,
 it is unaffected by any subsequent requests that are executed,
-including the
-.BR .bd ,
-.BR .cs ,
-.BR .tkf ,
-.BR .tr ,
+including
+.BR bd ,
+.BR cs ,
+.BR tkf ,
+.BR tr ,
 or
-.B .fp
+.B fp
 requests.
 .
 Normally,
-glyphs are constructed from input characters immediately before the
-glyph is added to the current output line.
+glyphs are constructed from characters immediately before the glyph is
+added to an output line.
 .
 Macros,
 diversions,
 and strings are all,
 in fact,
 the same type of object;
-they contain lists of input characters and glyphs in any combination.
+they contain a sequence of intermixed character and glyph nodes.
 .
-Special characters can be both: before being added to the output,
-they act as input entities;
-afterwards,
-they denote glyphs.
+Special characters transform from one to the other:
+before being added to the output,
+they behave as characters;
+afterward,
+they are glyphs.
 .
-A glyph does not behave like an input character for the purposes of
-macro processing;
-it does not inherit any of the special properties that the input
-character from which it was constructed might have had.
+A glyph node does not behave like a character node when it is processed
+by a macro:
+it does not inherit any of the special properties that the character
+from which it was constructed might have had.
 .
-Consider the following example.
+For example,
+the input
 .
 .RS
 .EX
@@ -5503,17 +5506,21 @@ Consider the following example.
 .EE
 .RE
 .
-It prints
+produces
 .RB \[lq] \[rs]\[rs] \[rq]
-in
-.IR groff ;
-each pair of input backslashes is turned into one output backslash and
-the resulting output backslashes are not interpreted as escape
-characters when they are reread.
+in GNU
+.IR troff . \" GNU
+Each pair of backslashes becomes one backslash
+.I glyph;
+the resulting backslashes are thus not interpreted as escape
+.I characters
+when they are reread as the diversion is output.
 .
-.RI AT&T\~ troff
-would interpret them as escape characters when they were reread and
-would end up printing one
+AT&T
+.I troff \" AT&T
+.I would
+interpret them as escape characters when rereading them and end up
+printing one
 .RB \[lq] \[rs] \[rq].
 .
 .