It's useCapture:
If true, useCapture indicates that the user wishes to
initiate capture. After initiating
capture, all events of the specified
type will be dispatched to the
registered listener before being
dispatched to any EventTargets beneath
it in the DOM tree. Events which are
bubbling upward through the tree will
not trigger a listener designated to
use capture. See DOM Level 3 Events
for a detailed explanation.
