where do dnf plugins go?

[Tom Horsley]

The DNF documentation desperately attempts to avoid actually
saying anything :-(. For pluginpath it says:

List of directories that are searched for plugins to load. Plugins found in any of the directories in this configuration option are used. The default contains a Python version-specific path.

The installed /etc/dnf/dnf.conf file doesn't explicitly say anything
about pluginpath, so it must be hard coded somewhere.

So what the heck is the actual contents of this pluginpath config
setting on fedora 22? Where do I install a .py module if I'm
trying to write my own plugin?