when is the /etc/kde4/kdm/Xreset script automatically executed?

On a system running the K Display Manager, when is the /etc/kde4/kdm/Xreset script automatically executed?

A.
When KDM starts

B.
When a users x session exits

C.
When KDM crashes

D.
When x is restarted

E.
When x crashes

Explanation:
From the man pages:
/etc/kde4/kdm/Xreset script to run as root after session exits