docs: def format_diff_xml(a_xml, b_xml):
      """Create a diff between two XML documents.
  
      Args:
        a_xml: str
        b_xml: str
  
      Returns:
        str : `Differ`-style delta
  
      """
      return '\n'.join(
          difflib.ndiff(
              reformat_to_pretty_xml(a_xml).splitlines(),
              reformat_to_pretty_xml(b_xml).splitlines(),
          )
      )