At 2020-11-11T16:34:15+0100, Alejandro Colomar (man-pages) wrote: > Thanks, Branden! > > And [+4n] is because you can also indent negatively? > But I guess I can omit [+] safely always. Yes. The unary plus is redundant for both .RS and .in. I see it used much more frequently with .in requests, though. I think it has to do with the greater awareness of formatter state one has to maintain when writing in "raw" roff requests. People include the plus as a form of documentation. You can indent negatively, and even to an absolute horizontal page position (with the '|' prefix). I don't see this done in real world man pages and I sure don't encourage it before the question of how well non-roff man page renderers (like mandoc) handle it. Here's how RS is defined in V7 Unix's tmac.an: ' # increase relative indent .de RS .nr ]\\n+()p \\n()I .nr )\\n()p \\n()R .ie !"\\$1"" .nr )R +\\$1n .el .nr )R +\\n()I .nr )I .5i .}E .. And here's groff's definition of the same macro, which hasn't changed in 20 years[2]. .de1 RS . nr an-saved-margin\\n[an-level] \\n[an-margin] . nr an-saved-prevailing-indent\\n[an-level] \\n[an-prevailing-indent] . ie \\n[.$] .nr an-margin +(n;\\$1) . el .nr an-margin +\\n[an-prevailing-indent] . in \\n[an-margin]u . nr an-prevailing-indent \\n[IN] . nr an-level +1 .. The leading plus sign when the macro argument $1 is interpolated ensures that if the caller doesn't supply a sign, the value will be interpreted as an increment when updating the register value. This is part of general register management syntax rather than anything to do with indentations or page formatting. An example with very simple register settings may help elucidate this. $ nroff .nr A 2 .nr B 3 .nr A +5 .nr B 5 .tm \nA 7 .tm \nB 5 (I'm sort of making nroff work like a REPL here--an underrated approach to learning it, in my opinion. I typed the requests, and nroff [really groff] wrote the "7" and "5" to standard error.) The interesting thing to me is that .RS in V7 doesn't do any indentation itself; instead it uses registers a bit differently. And the register names are limited to a two-character name length. For the attached document I get identical output[3] from groff and Heirloom Doctools troff, which is a direct descendant of the AT&T implementation. Regards, Branden [1] https://minnie.tuhs.org/cgi-bin/utree.pl?file=V7/usr/lib/tmac/tmac.an [2] 19 years for the very first line, because groff introduced the 'de1' request at that time. [3] modulus groff's use of SGR escapes instead of overstriking to achieve bold output; see grotty(1).
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