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From: kim@enea.UUCP
Newsgroups: net.unix-wizards
Subject: Re: nroff - help wanted - (nf)
Message-ID: <419@enea.UUCP>
Date: Thu, 28-Jun-84 22:00:15 EDT
Article-I.D.: enea.419
Posted: Thu Jun 28 22:00:15 1984
Date-Received: Thu, 28-Jun-84 04:08:58 EDT
Sender: notes@enea.UUCP
Organization: ENEA DATA, Sweden
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#R:kvvax4:-40700:enea:600007:000:1338
enea!kim    Jun 21 15:34:00 1984

>>	According to the [nt]roff manual, the \! mechanism should
>>	enable you to put anything in the outputfile (par 10.7),
>>	so why not a formfeed???

Sorry, that does not work.
A \! at the beginning of a line simply means that the rest of 
the line is read in 'copy mode' and transparently output without the \!.

But all control characters except STX, ETX, ENQ, ACK, and BEL are
ignored already on input (par 10.1 in Ossanna's manual Oct 11, 1976).
In System V, SI, SO, and ESC are also accepted, but this is undocumented.

In 4.xBSD, the control characters that are not ingnored on input
still have to be translated to some printable character by the
.tr command in order to appear in the output.
In System V, however, BEL, SI, SO, and ESC are transferred directly to
the output if not translated by .tr, but STX, ETX, ENQ, ACK disappear.
This is also undocumented.

If one wishes to extend the list of control characters that may be
output by nroff, the tables to modify are in the routines
getch0() in n1.c, and ptout1() in n10.c.
Warning: since nroff assumes that getch0() cannot return all values
in the interval 001-033, it uses some of them for internal purposes.
For example, to accept escape characters in 4.xBSD nroff,
the value of the symbol ESC in tdef.hd must be changed.

				Kim Walden
				{decvax,philabs}!mcvax!enea!kim