If I do xset dpms 600 3600 7200 , it blanks my screen after 10 minutes of inactivity. Questions How does X11 know how long I've been idle, and how can I access this idle time programatically? I couldn't get xprintidle to install, perhaps because X11 no longer has an XIDLE extension? Googling suggested looking at "man xscreensaver", but I couldn't find anything useful there.

How does X11 xscreensaver know how long I've been idle (xprintidle unhelpful)

If I do xset dpms 600 3600 7200, it blanks my screen after 10 minutes of inactivity.

How does X11 know how long I've been idle, and how can I access this idle time programatically?
I couldn't get xprintidle to install, perhaps because X11 no longer has an XIDLE extension?

Googling suggested looking at "man xscreensaver", but I couldn't find anything useful there.