def _referenced_object_ids
      ids = []
      _all_attributes.each do |attr|
        value = instance_variable_get(('@' + attr.to_s).to_sym)
        ids << value.id if value && value.respond_to?(:is_poxreference?)
      end
      ids
    end
def _referenced_object_ids
      ids = []
      _all_attributes.each do |attr|
        value = instance_variable_get(('@' + attr.to_s).to_sym)
        ids << value.id if value && value.respond_to?(:is_poxreference?)
      end
      ids
    end
Return a list of all object IDs that the attributes of this instance are
 referencing.
 @return [Array of Integer] IDs of referenced objects