For information on converting to InterSystems IRIS, see the
InterSystems IRIS Adoption Guide
and the InterSystems IRIS In-Place Conversion Guide,
both available on the WRC Distributions page (login required).
Ensures %ValidateObject() is called for this node and all its nested
This works depth-first, so all nested elements are validated before the nesting element
itself gets validated. Therefore, %OnValidateObject() methods may assume
nested elements are fully validated.