groff: Preprocessors in man pages
4.1.6 Preprocessors in 'man' pages
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If a preprocessor like 'gtbl' or 'geqn' is needed, it has become common
usage to make the first line of the man page look like this:
'\" WORD
Note the single space character after the double quote. WORD consists
of letters for the needed preprocessors: 'e' for 'geqn', 'r' for
'grefer', 't' for 'gtbl'. Modern implementations of the 'man' program
read this first line and automatically call the right preprocessor(s).