Path: utzoo!attcan!uunet!lll-winken!lll-tis!helios.ee.lbl.gov!pasteur!ucbvax!ucsd!rutgers!mit-eddie!killer!dcs!wnp
From: wnp@dcs.UUCP (Wolf N. Paul)
Newsgroups: comp.text
Subject: Re: troff magic
Message-ID: <191@dcs.UUCP>
Date: 2 Sep 88 05:01:55 GMT
References: <597@intvax.UUCP>
Reply-To: wnp@dcs.UUCP (Wolf N. Paul)
Organization: DCS, Dallas, Texas
Lines: 35

In article <597@intvax.UUCP> davidson@intvax.UUCP (William M. Davidson) writes:
>I noticed an example in the Troff Reference Manual that looks strange
>and I have no idea how it works.
>
>In chapter 11, the following macro example was given to draw a line under
>a string:
>
>.de us
>\\$1\l'|0\\(ul'
>..
>
>I understand everything except the "|0".  I assume it is the
>N argument for the line drawing function, \l'Nc'.
>
>It does work so it is not a typo in the manual.

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
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