Wring Manpages
Where to find useful documentation for writing manpages.
Linux man-pages project
man-pages(7) - conventions for writing Linux manpages. Which sections go where, etc
man(7), mdoc(7) - man-pages ' description of the relevant Groff macro packages
Groff
man Macro Package from the Groff manual
groff_man(7) - same as the above, in manpage format
groff_mdoc(7) - Groff's documentation for their mdoc macro package.