on [<modes>]window_kill [<serial#>] [-|^]<match> { <action> }

This hook is triggered after a window has been killed. By the time that this is triggered, the window has been irrevocably destroyed, and cannot be used. You can use this hook to clean up after your own data that may be keyed on the window's refnum.

If it's necessary to know that a window is being killed before it is destroyed, use ON WINDOW_BEFOREKILL.

ON WINDOW_KILL already existed in ircII2.1.5g. The current semantics (with two params) first appeared in EPIC4-1.1.11.