docs: public void checkConstraints(String checkLevel) throws ConstraintException
      {
          // now checking constraints
          FieldDescriptorConstraints      fieldConstraints = new FieldDescriptorConstraints();
          ReferenceDescriptorConstraints  refConstraints   = new ReferenceDescriptorConstraints();
          CollectionDescriptorConstraints collConstraints  = new CollectionDescriptorConstraints();
  
          for (Iterator it = getFields(); it.hasNext();)
          {
              fieldConstraints.check((FieldDescriptorDef)it.next(), checkLevel);
          }
          for (Iterator it = getReferences(); it.hasNext();)
          {
              refConstraints.check((ReferenceDescriptorDef)it.next(), checkLevel);
          }
          for (Iterator it = getCollections(); it.hasNext();)
          {
              collConstraints.check((CollectionDescriptorDef)it.next(), checkLevel);
          }
          new ClassDescriptorConstraints().check(this, checkLevel);
      }