Why are tmac/tty-char.tmac and tmac/tty.tmac separate files? They both seem to serve essentially the same purpose: providing fallback character sequences for characters that may not exist in the terminal environment's encoding (especially the limited sets available to ASCII and Latin-1).
But they are called from different places: grotty's man page specifies that troffrc loads tty.tmac automatically for any terminal device; thus, these two commands, using a character defined in tty.tmac, both produce the same output: $ echo '\[lh]' | nroff | cat -s $ echo '\[lh]' | groff -Tascii | cat -s But, as its man page says, the nroff script specifies tty-char.tmac, which means that whether this file is loaded depends on which command is used. This example uses a character defined in tty-char.tmac: $ echo '\[dg]' | nroff | cat -s <*> $ echo '\[dg]' | groff -Tascii | cat -s troff: <standard input>:1: warning: can't find special character 'dg' $ There may be a valid reason for this separation, but I'm not sure what it is. What are the use cases where a user wants one set of definitions but not the other? A comment in tty-char.tmac (reiterated on the nroff man page) gives some small hint: "the optical appearance of the definitions contained in this file is inferior... to those of the replacement characters defined in the file tty.tmac." But this must be a statement in general terms, as only one character is defined in both files: $ egrep -h '^\.(f|tty-)char ' tmac/tty*.tmac | cut -f2 -d\ > /tmp/sym $ diff <(sort /tmp/sym) <(sort -u /tmp/sym) 232d231 < \[sd] $ rm /tmp/sym $ fgrep '\[sd]' tmac/tty* tmac/tty-char.tmac:.tty-char \[sd] '' tmac/tty.tmac:.fchar \[sd] \[dq] (And in this case, which fallback definition of the arc-second sign is "superior" is a judgment call, but whichever one it is ought to be used across the board. Both are pure ASCII; \[dq] is ASCII 34, the straight double-quote character.) So the upshot isn't that using only tty.tmac gives "better" results; the upshot is that using only tty.tmac leaves some character escapes undefined for terminals, provoking warnings and omitting information from the output. And in a couple of cases, tty.tmac (the file that's always loaded) seems to presume the loading of tty-char.tmac (the file that's NOT always loaded): tty.tmac defines two glyphs in terms of \[rn], but \[rn] is defined for terminal devices in tty-char.tmac. Does these files being separate serve some purpose, or is it an evolutionary accident?
