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).