code: def add_missing_children(required_children, element_children):
      
      element_tags = [element.tag for element in element_children]
      # Loop through the elements that should be in the form.
      for contained_element in required_children:
          # If the element doesn't exist in the form,
          # add the element to the children.
          if contained_element not in element_tags:
              try:
                  added_child = PYUNTL_DISPATCH[contained_element](content='')
              except:
                  added_child = PYUNTL_DISPATCH[contained_element]()
              element_children.append(added_child)
      return element_children
docs: Determine if there are elements not in the children
      that need to be included as blank elements in the form.