Libxss provides an x window system client interface to the mit-screen-saver extension to the x protocol.

the screen saver extension allows clients behaving as screen savers to register themselves with the x server, to better integrate themselves with the running session.

more information about x.org can be found at:

this module can be found at git://anongit.freedesktop.org/git/xorg/lib/libscrnsaver