The MouseEnter event occurs when the mouse cursor enters an ActiveField. A corresponding MouseExit event occurs when the mouse cursor leaves the field.

MouseEnter events do not occur when the mouse is captured (that is, during a drag-and-drop operation). If a MouseEnter event occurs and the corresponding MouseExit event has not occurred when the mouse is captured, a MouseExit event will be generated when the mouse becomes captured. Thus, every MouseEnter event is followed by a matching MouseExit event. When a MouseExit event is generated because the mouse becomes captured, the associated ReasonCode is RC_MOUSECAPTURED.