This is my attempt to revise the figure by working _with_ tbl(1)
and nroff(1)/troff(1) features instead of fighting them or enduring
suffering and significant maintenance challenges.
* Stop using mn(7) display macros; the other two figures didn't and they
don't appear to be buying much.
* Use `tr` character translation feature to temporarily remap characters
for clarity of input. It's convenient to input ordinary characters
here since the table's contents are (mostly) character-cell art.
Remap `-` to minus sign and `@` to the "reverse solidus" special
character. (`\` is the default *roff escape character. It can be
changed, but attempting that seems hopeless inside a tbl(1) table.)
Revert the translations after the table. (There's nothing special
about `@`; you could choose any other character that isn't otherwise
needed in the table.)
* Use `box` region option as with Figures 1 and 2. Perhaps this wasn't
done because those are meant to depict a terminal window, but Figure 2
depicts only part of one, so its top border is a fib.
* Use `expand` region option to obtain roughly the same spread-out
effect that the table was laboriously using empty columns and the `e`
column modifier for.
* Consequently, reduce the column count to 2; both have real content.
* Annotate both keycap diagrams--in part for clarity, but also to make
it more obvious that the columns will balance in width.
These changes don't require GNU extensions to *roff or tbl except,
arguably, the \(rs special character. But support for that special
character identifier is easily added to any device-independent troff;
see §23.2 of CSTR #54 (Kernighan 1992 revision) or groff_font(5). Or I
can prepare a patch--just ask me. But given that no one seems to have
complained about the disaster that AT&T tbl/nroff must have been making
of Figures 1 and 2 for decades, I'm guessing this isn't a practical
concern. Any if it _is_ a problem, `\e` can be used instead of `\(rs`.
(I didn't use it because what is wanted is the backslash glyph
specifically [to mirror `/`], not "the escape character". But given the
constraints imposed by use of tbl(1), it's an academic point.)
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