[log entry:] > It was probably unnecessary to hedge against future changes in standard > typographical vertical spacing. The 120% ratio convention is older than > I am and I expect it to long survive me. ... [added text:] > +In ordinary circumstances, this quantity is 120% of the type size. The
This sentence feels a little misleading. As your commit log entry points out, this is the *typographic* convention. But this sentence appears in groff documentation, and nothing in groff makes this 120% "ordinary": the user must explicitly specify a .vs value that is 120% of her .ps value in order to make this true in troff. Just as likely, the user will specify both of these values as integers (e.g., 12p and 14p), which works out to close to but not precisely 120%. (As noted in the http://savannah.gnu.org/bugs/?61710 discussion, groff itself and many full-service macro packages lack a built-in mechanism to set the line spacing as a given percentage of the type size; -me and -mom are two exceptions that do enable this.) The ratio of the startup values of these two quantities is 120%, but I don't think "by default" and "in ordinary circumstances" are synonymous; the latter phrase can be construed as saying that groff, in at least some circumstances, maintains this percentage after a change to the type size. One alternate way to phrase this (if you're not happy with reverting to the original wording) could be, "Traditionally, typesetters have set this quantity to 120% of the type size." This acknowledges both the typographical precedent you cite in the commit log, and the fact that the user must explicitly make it happen in groff.
