def _extended(self):
        """
        The extension data of a multipart body part are in the following order:

          1. body parameter parenthesized list
               A parenthesized list of attribute/value pairs [e.g., ("foo"
               "bar" "baz" "rag") where "bar" is the value of "foo", and
               "rag" is the value of "baz"] as defined in [MIME-IMB].

          2. body disposition
               A parenthesized list, consisting of a disposition type
               string, followed by a parenthesized list of disposition
               attribute/value pairs as defined in [DISPOSITION].

          3. body language
               A string or parenthesized list giving the body language
               value as defined in [LANGUAGE-TAGS].

          4. body location
               A string list giving the body content URI as defined in
               [LOCATION].
        """
        result = []
        headers = self.message.getHeaders(
            False, 'content-language', 'content-location',
            'content-disposition')

        result.append(self._unquotedAttrs())
        result.append(self._disposition(headers.get('content-disposition')))
        result.append(headers.get('content-language', None))
        result.append(headers.get('content-location', None))

        return result

        The extension data of a multipart body part are in the following order:

          1. body parameter parenthesized list
               A parenthesized list of attribute/value pairs [e.g., ("foo"
               "bar" "baz" "rag") where "bar" is the value of "foo", and
               "rag" is the value of "baz"] as defined in [MIME-IMB].

          2. body disposition
               A parenthesized list, consisting of a disposition type
               string, followed by a parenthesized list of disposition
               attribute/value pairs as defined in [DISPOSITION].

          3. body language
               A string or parenthesized list giving the body language
               value as defined in [LANGUAGE-TAGS].

          4. body location
               A string list giving the body content URI as defined in
               [LOCATION].
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/mail/imap4.py