[bug #62593] clarify description of end-of-sentence detection

[G. Branden Robinson]

Follow-up Comment #16, bug #62593 (project groff):


[comment #12 comment #12:]
> [comment #7 comment #7:]
> > A "space" as I'm proposing to use it can always be discarded
> > at a break and a horizontal motion cannot be.
> 
> True but slightly misleading: most of the things groff now deems horizontal
motions are not breakpoints, so groff would only break there if there were
_also_ a space (or a \:) adjacent to it, which will rarely be the case.

That's true, but as far as my testing so far shows, motions always end up in
device-independent output, and spaces--including the non-breaking space
\~--don't, necessarily (they can be discarded).

See attachments.  They are four nearly identical files: one uses a trailing
space on a line, one \h, one \~, and one "\ " (a.k.a. \SP, \space).  Format
them with "groff -Z", and diff the outputs.


$ diff -u space.grout motion.grout && echo no difference
--- space.grout 2022-06-18 18:08:55.097349267 -0500
+++ motion.grout        2022-06-18 18:09:04.009294632 -0500
@@ -19,6 +19,7 @@
 Cfl
 h5560
 te.
+h10000
 n12000 0
 x trailer
 V792000
$ diff -u space.grout nbspace.grout && echo no difference
no difference
$ diff -u space.grout fixedspace.grout && echo no difference
--- space.grout 2022-06-18 18:08:55.097349267 -0500
+++ fixedspace.grout    2022-06-18 19:00:17.675332923 -0500
@@ -19,6 +19,7 @@
 Cfl
 h5560
 te.
+h2500
 n12000 0
 x trailer
 V792000


> So drawing a distinction that doesn't have much real-world application seems
like it maybe doesn't serve readers best,

Whether a motion command gets sent to device-independent output matters for
things like the output comparison operator.

> and also might imply a breakability that these characters don't have.

I don't think I understand your point here.  Can you rephrase?

> Further, terms like "figure space" are well known outside groff, and it
serves readers knowledgeable about typography to use the terms standard in the
art.

I have no problem making reference to these as descriptive material when
documenting the escape sequences; I already started down that road with "thin
space" and "hair space".

Within the domain of *roff operation, however, there is a tangible, measurable
difference between spaces and horizontal motions, as I tried to illustrate
above.
 
> Essentially moot, since I get your point, but I don't understand this
example: with adjusting turned off, whether there is "space" at the end of an
output line is invisible.  And this snippet's terminal output has no lines
with trailing space characters.

Yes, I recognize that it didn't clearly enough communicate the point I was
trying to get across.  See if you find the foregoing (and attached) more
illuminating.

Regards,
Branden

(file #53316, file #53317, file #53318, file #53319)

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Additional Item Attachment:

File name: 62593-space.roff               Size:0 KB
    <https://file.savannah.gnu.org/file/62593-space.roff?file_id=53316>

File name: 62593-nbspace.roff             Size:0 KB
    <https://file.savannah.gnu.org/file/62593-nbspace.roff?file_id=53317>

File name: 62593-motion.roff              Size:0 KB
    <https://file.savannah.gnu.org/file/62593-motion.roff?file_id=53318>

File name: 62593-fixedspace.roff          Size:0 KB
    <https://file.savannah.gnu.org/file/62593-fixedspace.roff?file_id=53319>



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