Path: utzoo!attcan!uunet!husc6!cmcl2!nrl-cmf!ames!pasteur!ucbvax!hplabs!hpda!hpcupt1!hpsal2!morrell
From: morrell@hpsal2.HP.COM (Michael Morrell)
Newsgroups: comp.text
Subject: Re: troff magic
Message-ID: <2610012@hpsal2.HP.COM>
Date: 2 Sep 88 22:46:29 GMT
References: <597@intvax.UUCP>
Organization: HP System Architecture Lab, Cupertino
Lines: 34

/ hpsal2:comp.text / wnp@dcs.UUCP (Wolf N. Paul) / 10:01 pm  Sep  1, 1988 /

As far as I can tell, this assumes that you are at the beginning of
an output line. It prints the argument ( $1 ), then draws a line from the
current print position (i.e. immediately after the argument) to absolute
horizontal position 0 (i.e., back to the beginning of the line. It also
leaves the current print position to be at the beginning of the line --
thus it makes a good example, but is of little practical value. 

The syntax is explained in section 3.1.3 of the Nroff/Troff Users Manual,
entitled "Numerical Parameter Input":

  The absolut position indicator (|) may be prepended to a numer N
  to generate the distance to the vertical or horizontal place N.

Thus, |0 is the absolute zero position; since the line drawing function
takes a horizontal measurement, it is here the absolute horizontal zero.

-- 
Wolf N. Paul * 3387 Sam Rayburn Run * Carrollton TX 75007 * (214) 306-9101
UUCP:     killer!dcs!wnp                 ESL: 62832882
DOMAIN:   dcs!wnp@killer.dallas.tx.us    TLX: 910-380-0585 EES PLANO UD
----------

Try reading later in the same paragraph:

  For all other requests and functions [including \l], |N becomes the distance
  from the current horizontal place on the INPUT line to the horizontal place
  N.

This macro always works since the argument is at the beginning of its input
line.

   Michael