current-idle-timecurrent-idle-time is a built-in function in `
C source code'.
Return the current length of Emacs idleness, or nil.
The value when Emacs is idle is a list of four integers (HIGH LOW USEC PSEC)
in the same style as (current-time).
The value when Emacs is not idle is nil.
PSEC is a multiple of the system clock resolution.