Re: Differences in `ne` and `bp` line-breaking behavior

[G. Branden Robinson]

Hi Steve,

At 2024-12-04T13:28:48-0500, Steve Izma wrote:
> On Wed, Dec 04, 2024 at 12:00:52PM -0500, Douglas McIlroy wrote:
> > Subject: Re: Differences in `ne` and `bp` line-breaking behavior
> > 
> > I don't see this wording as an improvement:
> > 
> > >   .ne d    Advance drawing position to the next vertical
> > >            position trap and spring the trap, if it is
> > >            nearer than distance d (default scaling unit v).
> > 
> > The proposal uses nonstandard terminology ("drawing position"),
> > and is ambiguously worded. It is easy to misread "if" as applying
> > only to the "spring" clause rather than to the compound of
> > "advance" and "spring".
> 
> I'm not sure about "drawing position",

It's my term; folks can blame me.

> but simply recasting the sentence clarifies or corrects the logic,
> e.g.:
> 
> .ne d   If the next vertical position trap is nearer than
>       distance d (default scaling unit v), advance drawing
>       position to it and spring the trap.
>       
> Maybe "advance the current vertical position to it", since I
> believe that \n[.d] becomes equal to the trap position once it's
> sprung.

Not inside a diversion trap, oddly.  See the example I posted earlier in
this thread.  Nevertheless the claim seems otherwise consistent with
user experience.

> > Also .ne is effective in the absence of traps, a fact that groff(7)
> > misses, too.
> 
> This is news to me. Does it mean that the default page length
> automatically creates a trap? Or does .ne have a side effect?

As far as I know, Doug is referring only to what I have christened the
"implicit page trap".

If something more is going on, I would like to know, so I can experiment
on it and document it.

> The most erroneous stories are those we think we know best – and
> therefore never scrutinize or question.
>     -- Stephen Jay Gould, *Full House: The Spread of Excellence
>        from Plato to Darwin*, 1996

Excellent choice of quote for this discussion.

Regards,
Branden

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