ChildMouseExit Event
The ChildMouseExit event occurs when the mouse cursor leaves a field, or when the mouse is captured. If the ChildMouseExit event occurs because the mouse is captured, the associated ReasonCode is RC_MOUSECAPTURED.
on ChildMouseExit [compositefieldname]
compositefieldname is optional if you specify the event in a field script for a composite field, or if the composite field is the frame's top form.