A sub-field shape used inside an object's fields or an array's of —
lighter than FieldEntry: no initialValue/editable/required,
since a sub-field's value comes from the parent. An object kind requires
non-empty fields and no of; an array kind requires non-empty of and
no fields; every other kind requires neither — enforced at parse, not
visible in this type.
A sub-field shape used inside an
object'sfieldsor anarray'sof— lighter than FieldEntry: noinitialValue/editable/required, since a sub-field's value comes from the parent. Anobjectkind requires non-emptyfieldsand noof; anarraykind requires non-emptyofand nofields; every other kind requires neither — enforced at parse, not visible in this type.