Re: End-of-sentence spacing

[G. Branden Robinson]

At 2020-12-21T17:07:10-0600, Dave Kemper wrote:
> On 12/20/20, Peter Schaffter <peter@schaffter.ca> wrote:
> > Perhaps I should have been more verbose and written: According
> > to the info(1) manual, initially both the WORD_SPACE_SIZE and
> > SENTENCE_SPACE_SIZE are 12; since this prevents SS from being larger
> > than WS, it effectively disables sentence spacing.
> 
> Unfortunately, the info manual uses the term "sentence space" not in
> its conventional meaning of "the amount of space between sentences"
> but as "the amount of space to *add* to the word space between
> sentences."  The info manual does spell out this meaning, so there's
> technically no ambiguity, but "sentence space" having a different
> meaning from normal typographic usage seems needlessly confusing.

I thought you and I worked to fix this earlier this year?

Hmm, yes, I see there are some straggling cases remaining, including one
in my recent rewrite of section 5.1.  Sigh.

For the sake of the lurkers and those unfortunate souls who don't run
groff straight out of git HEAD, here's the current discussion of this
topic in the info(1) manual.

I urge anyone who finds the following insufficiently clear to go out in
groff 1.23.0 to speak up.

 -- Request: .ss word-space-size [sentence-space-size]
 -- Register: \n[.ss]
 -- Register: \n[.sss]
     Set the sizes of spaces between words and sentences.  Their units
     are twelfths of the space width parameter of the current font.
     Initially both the WORD-SPACE-SIZE and SENTENCE-SPACE-SIZE are 12.
     Negative values are not permitted.  The request is ignored if there
     are no arguments.

     The first argument, the inter-word space size, is a minimum; if
     automatically adjusted, it may increase.

     The optional second argument sets the amount of additional space
     separating sentences on the same output line in fill mode.  If the
     second argument is omitted, SENTENCE-SPACE-SIZE is set to
     WORD-SPACE-SIZE.

     The read-only registers '.ss' and '.sss' hold the values of minimal
     inter-word space and additional inter-sentence space, respectively.
     These parameters are associated with the current environment (*note
     Environments::), and rounded down to the nearest multiple of 12 on
     terminal output devices.

     Additional inter-sentence spacing is used only in fill mode, and
     only if the output line is not full when the end of a sentence
     occurs in the input.  If a sentence ends at the end of an input
     line, then both an inter-word space and an inter-sentence space are
     added to the output; if two spaces follow the end of a sentence in
     the middle of an input line, then the second space becomes an
     inter-sentence space in the output.  Additional inter-sentence
     space is not adjusted, but the inter-word space that always
     precedes it may be.  Further input spaces after the second, if
     present, are adjusted as normal.

     If a second argument is never given to the 'ss' request, GNU
     'troff' separates sentences as AT&T 'troff' does.  In input to GNU
     'troff', as with AT&T 'troff', a sentence should always be followed
     by either a newline or two spaces.

     A related application of the 'ss' request is to insert discardable
     horizontal space; i.e., space that is discarded at a line break.
     For example, some footnote styles collect the notes into a single
     paragraph with large spaces between each.

          .ie n .ll 50n
          .el   .ll 2.75i
          .ss 12 48
          1. J. Fict. Ch. Soc. 6 (2020), 3\[en]14.
          2. Better known for other work.

     The result has obvious inter-sentence spacing.

          1. J. Fict. Ch. Soc. 6 (2020), 3-14.     2. Better
          known for other work.

     If _undiscardable_ space is required, use the '\h' escape.

Regards,
Branden

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