def duplicate_child_info(child_ref)
      @title ||= child_ref.title
      @type ||= child_ref.subset_operators
      @definition ||= child_ref.definition
      @status ||= child_ref.status
      @code_list_id ||= child_ref.code_list_id
      @temporal_references = child_ref.temporal_references if @temporal_references.empty?
      @subset_operators ||= child_ref.subset_operators
      @variable ||= child_ref.variable
      @value ||= child_ref.value
    end
def duplicate_child_info(child_ref)
      @title ||= child_ref.title
      @type ||= child_ref.subset_operators
      @definition ||= child_ref.definition
      @status ||= child_ref.status
      @code_list_id ||= child_ref.code_list_id
      @temporal_references = child_ref.temporal_references if @temporal_references.empty?
      @subset_operators ||= child_ref.subset_operators
      @variable ||= child_ref.variable
      @value ||= child_ref.value
    end
Duplicates information from a child element to this data criteria if none exits.
 If the duplication requires that come values should be overwritten, do so only in the function calling this.