Hi Tadziu, At 2024-07-24T22:27:31+0200, Tadziu Hoffmann wrote: > > > a "margin" measures an extent of whitespace (or "negative space"), > > > whereas the `sp` request positions the _text baseline_, > > The first is correct and the second incorrect for [g]troff.
I will defend my formulation. `sp` _does_ position the text baseline, period. Where, exactly, it puts it sometimes overturns the user's intuition. > In troff (and nroff), if you say > > .sp |0 > > then this does not mean "put the baseline at the top of the page" > but rather "leave zero space above the text", and correspondingly Agreed. > .sp |50p > > means "leave 50 pt of space above the text", as you would expect > for margins. Thus, troff's model somewhat follows the concepts > of metal typesetting. Yes. Equally `.sp 1v` (which is really the same as `.sp`) leaves 1v of space above the next output line. $ nroff <<EOF foo .br bar .sp 1v baz .pl \n(nlu EOF foo bar baz The baselines of "foo" and "bar" are 1v apart, but those of "bar" and "baz" are 1v+1v=2v apart. Where I, and apparently sometimes others, usually screw this up is when computing distances from the page _bottom_. Hence this bit of diff-business that I committed to my working copy today: .de fo \" page footer -' sp .5i +' sp .5i-1v . tl ''%'' . bp .. [...] .wh -1i fo \" trap 1 inch from bottom If you want the footer title to sit half an inch from the bottom of a page, you have to adjust it by 1v as shown. > Of course, troff simplifies this a bit, in the first case by putting > the baseline at 1 vee below the top of the page, and in the second > case at 50 pt + 1 vee. Yes. To Peter Schaffter's grief. https://savannah.gnu.org/bugs/?61507 [snip] I have no gripe with your example; I simply think you inferred something different from my claim than I was intending. Collectively, our best efforts at explanation are in the groff Texinfo manual, groff(7), and roff(7). If those could use improvement, I'm listening. Regards, Branden
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