docs: def _make_attr_element_from_resourceattr(parent, resource_attr_i):
      """
          General function to add an attribute element to a resource element.
      """
  
      attr = _make_attr_element(parent, resource_attr_i.attr)
  
      attr_is_var    = etree.SubElement(attr, 'is_var')
      attr_is_var.text = resource_attr_i.attr_is_var
  
      return attr