Sometimes it is desirable to fill a tab stop with a given glyph,
but also use tab stops normally on the same output line. An example is
a table of contents entry that uses dots to bridge the entry name with
its page number, which is itself aligned between tab stops. The
roff language provides leaders for this
A leader character (ISO and EBCDIC code point 1, also known as SOH or “start of heading”), behaves similarly to a tab character: it moves to the next tab stop. The difference is that for this movement, the default fill character is a period ‘.’.
Interpolate a leader in copy mode; see Copy Mode.
Set the leader repetition character to the ordinary or special character
c. Recall Tabs and Leaders: when encountering a leader
character in the input, the formatter writes as many dots ‘.’ as
are necessary until
reaching the next tab stop; this is the leader definition
character. Omitting c unsets the leader
character. With no argument, GNU
troff treats leaders the same
as tabs. The leader repetition character is associated with the
environment (see Environments). Only a single c is
recognized; any excess is ignored.
A table of contents, for example, may define tab stops after a section number, a title, and a gap to be filled with leader dots. The page number follows the leader, after a right-aligned final tab stop wide enough to house the largest page number occurring in the document.
.ds entry1 19.\tThe Prophet\a\t98 .ds entry2 20.\tAll Astir\a\t101 .ta .5i 4.5i +.5iR .nf \*[entry1] \*[entry2] ⇒ 19. The Prophet............................. 98 ⇒ 20. All Astir............................... 101