* On 2021 11 Aug 20:30 -0500, Dave Kemper wrote: > On 8/9/21, G. Branden Robinson <g.branden.robin...@gmail.com> wrote: > > > > \v'-.5'\s-4\&2\s0\v'.5' > > > > The use of \&, unnecessary here as far as I know, suggests to me that > > someone got burned by the magic syntax of the \s escape sequence. > > The \& is unnecessary for correct machine parsing, but it surely aids > human eyes, which could otherwise potentially misread \s-42. A > handful of users may have memorized the cutoffs for \s's magic, but > others would have to consult another manual to check. The \& makes it > immediately clear the "2" is not part of the "\s" escape.
In perusing CSTR #54 [1] in section 11.1 "Local Motions." the last
paragraph gives this example:
As an example, E2 could be generated by the
sequence E\s–2\v’–0.4m’2\v’0.4m’\s+2; note that the 0.4 em
vertical motions are at the smaller size.
In this way the author apparently intends to disambiguate the magic of
\s by following it immediately with \v, As the parameters to \v must be
quoted, the 2 becomes visually isolated and no need for \&. As noted,
the roff user must be careful to understand that \v now computes from
the smaller point size set by \s.
As I understand it, with macros the escapes would be "hidden" and the
ambiguity of the \s magic would not be evident to the roff author, e.g.
E\*[SUPER_START]2\*[SUPER_END], etc.
- Nate
[1] https://www.troff.org/54.pdf
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