Re: [Groff] : ASCII Minus Sign in man Pages

[Ingo Schwarze]

Hi Doug,

Doug McIlroy wrote on Mon, May 01, 2017 at 06:55:19PM -0400:
> Ingo Schwarze wrote:

>>  If you want a real minus sign (in particular in mathematical
>> formular as opposed to in programming language source code),
>> \- is not a good choise.

> This statement baffles me. That is exactly what \- is supposed
> to mean: the mathematical minus sign. In particular it is supposed
> to match + in width and weight. Are you saying that it no longer
> has that property and something else does?

Exactly.  Rendering of \- varies depending on software suite,
software version, macro set, and output device.

For example, in manual pages on -Tutf8 and -Tpdf output devices 
with modern groff, it renders as U+002D HYPHEN-MINUS, not as
U+2212 MINUS SIGN.

The character escape sequence \(mi always renders as U+2212 MINUS
SIGN on all implementations i'm aware of, as long as the selected
output device supports it; otherwise, it might of course fall back
to whatever the device provides.

In classical typesetting, it only mattered how the output looked.
Today, it also matters which Unicode codepoints you get.  Semantics
may differ even if the glyphs are almost indistinguishable.  U+002D
HYPHEN-MINUS and U+2212 MINUS SIGN will look very similar in many
fonts, but they are distinct characters.

Yours,
  Ingo