dh_undocumented is a debhelper program that is responsible for making symlinks to undocumented(7) for man pages that are not present in your package.
The program takes a list of man pages that should be symlinked to undocumented(7). It examines the extension to see what section the man page belongs in. After figuring this out, it generates the necessary symlinks.
The lists of man pages that need symlinks can be specified in two ways. Any man page names specified as parameters will be set up in the first package dh_undocumented is told to act on. By default, this is the first binary package in debian/control, but if you use -p, -i, or -a flags, it will be the first package specified by those flags.
Install undocumented man page symlinks for any man pages specified by command line parameters in ALL packages acted on. I doubt anyone will find this useful, it's here for consitency with other debhelper programs.
Install undocumented man page symlinks for each of these man pages into the first package acted on. (Or in all packages acted on if -A is specified.)