Per Acrobat JavaScript Reference Manual Field versus widget attributes for a listing of which action apply to the field and which are only available to the widget. Note: The setAction method can apply at the field or widget level, depending on the event. The Keystroke, Validate, Calculate, and Format events apply to fields. The MouseUp, MouseDown, MouseEnter, MouseExit, OnFocus, and OnBlur events apply to widgets. The checkThisBox, defaultIsChecked, isBoxChecked, and isDefaultChecked methods take a widget index, nWidget, as a parameter. If you invoke these methods on a Field object f that represents one specific widget, the nWidget parameter is optional (and is ignored if passed) and the method acts on the specific widget encapsulated by f.
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