Returns a list of nodes contained within this subform (inclusive)
that have a failed validation test.
Generates a list of all the invalid container objects, such as
afield, exclusion group, or subform, contained within descendants
of that subform. If the subform that this script method is called
on is itself invalid, that subform is included in the returned list.
The list is only generated on demand by recursively traversing the subform.
The returned list is in document order.
method does not return
the list of mandatory fields until after the submit has fired. If
the list of mandatory fields is required, the
be called first.
list of invalid container objects in the order they exist on the