Re: nroff mode paging inconsistencies

[G. Branden Robinson]

Hi Chuck,

At 2024-05-10T13:17:28-0500, Chuck Jungmann wrote:
> A macro I wrote exhibited rare misaligned formatting. While debugging
> it, I discovered some inconsistencies with page dimensions and offsets
> that I didn't expect from nroff output to a pager.
> 
> The alleged (maybe I don't understand something) inconsistencies
> pertain to values of various registers.  The register for page offset
> (\n[.o]) always reports a 0 value, as one would expect for an unpaged
> document.

I may not be understanding your report, but it sounds to me like you
expect the "page offset" to be a vertical measurement (perhaps distance
to the page bottom).

But it is not.  The page offset is a horizontal measurement, and indeed
for nroff output in GNU troff it is always zero by default.

Here's how our manual documents it.

--snip--
5.15 Line Layout

The following drawing shows the dimensions that gtroff uses for placing
a line of output onto the page. They are labeled with the request that
manipulates each dimension.

     -->| in |<--
        |<-----------ll------------>|
   +----+----+----------------------+----+
   |    :    :                      :    |
   +----+----+----------------------+----+
-->| po |<--
   |<--------paper width---------------->|

These dimensions are:

po
    Page offset—this is the leftmost position of text on the final
    output, defining the left margin.

in
    Indentation—this is the distance from the left margin where text is
    printed.

ll
    Line length—this is the distance from the left margin to right
    margin.
--end snip--

You can find the foregoing at this URL.

https://www.gnu.org/software/groff/manual/groff.html.node/Line-Layout.html

Does this help any?

Regards,
Branden

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