> Rare? Maybe. But not so rare that a macro package need not > be prepared for it.
I think leaders are meant to be used in conjunction with diversions. When they are used in already formatted text, all required dimensions are known, allowing n/troff to compute the number of leader character repetitions plus any possibly required additional space. See the attached example. Note that "\t" has one backslash, so it is evaluated as a tab while the diversion is being set up (the input is the "input line"), but "\\a" has two backslashes, so the leaders are applied when the diversion is output to the page (the formatted content of the diversion is the "input line").
.\" .\" ---------------------------------------------------------------- .ll 16c .po 2.5c .char \(LC .\h'1m' .lc \(LC .\" ---------------------------------------------------------------- .de CH .ll -10n .in 6n .ti -6n .ta 6n .fi \\$1.\t\c .di XX .. .\" ---------------------------------------------------------------- .de PG \\a\\$1 .br .di .in .ll .nf .ta \\n(.luR .XX .. .\" ---------------------------------------------------------------- .sp 2c \D'l \n(.lu 0' .br .CH 14 The Laureate Is Exposed to Two Assassinations of Character, a Piracy, a Near-Deflowering, a Near-Mutiny, a Murder, and an Appalling Colloquy Between Captains of the Sea, All Within the Space of a Few Pages .PG 222
