Docstring of the enumeration, formatted for documentation page.

def _intro_text(self):
        """Docstring of the enumeration, formatted for documentation page."""
        try:
            cls_docstring = self._clsdict['__doc__']
        except KeyError:
            cls_docstring = ''

        if cls_docstring is None:
            return ''

        return textwrap.dedent(cls_docstring).strip()