Re: [Groff] groff_char(7): Combination of characters vs. single unicode character

[Ted Harding]

On 15-Dec-2014 19:23:00 Carsten Kunze wrote:
> Hello,
> 
> when there is a unicode character for e.g. "not equal" (U+2260)
> why there is a combination of characters in groff_char(7) instead
> of unicode?  Is it intended for ASCII output?
> 
> Carsten

I presume you are referring (e.g.) to the item

 ?        \[!=]   notequal

(where the "?" displays in my xterm as an "=" with a "/" through it
-- not available in my mail agent) in the list of "Mathematical Symbols"
displayed by 'man groff_char'.

This notation "\[!=]" is intended for ASCII *input*; what happens
on output depends on the resources available for the output device,
and on what groff can access when formatting for a given output
device.

This kind of notation for characters goes back to close to the
origins of troff (though extended for groff), and enables the
designation of (essentially) arbitrary symbols/characters/objects
while using a text editor that does not necessarily extend beyond
ASCII. It is still very useful!!! You can set up something which
has no code whatever in any coding system (even unicode) and call
it something like "\[mychar]". I often do this (e.g. defining the
arbitrary glyph using PostScript code).

Example (not using PostScript in the definition, but depending
on PostScript metrics in the output; the "\[rs]" represents "\"
in the ouput to avoid escape-character complications):
===================

.char \[mychar] \Z'\h'0.1m'='\Z'\v'-0.265m'/'\Z'\v'0.415m'\[rs]'\
\Z'\h'0.5m'\v'-0.265m'\[rs]'\Z'\h'0.5m'\v'0.415m'/'\
\h'0.5m+\w'/'u'

The character \[mychar] doesn't represent anything!

===================

Best wishes to all,
Ted.

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E-Mail: (Ted Harding) <address@hidden>
Date: 15-Dec-2014  Time: 20:26:06
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