Initiates when a field or subform gains keyboard focus, whether caused by a form filler action (tabbing into a field or clicking in it) or by a script programmatically setting the focus.
You can use this event to provide help text or other messages to a form filler while entering the current field or subform. For example, if a field requires a value in a specific format, or if filling a field requires special instructions, you can use this event to provide a message to the form filler indicating the special needs.
See also 

enter event