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

          1. body MD5

             A string giving the body MD5 value as defined in [MD5].

          2. body disposition

             A parenthesized list with the same content and function as
             the body disposition for a multipart body part.

          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-md5', 'content-disposition',
            'content-language', 'content-language')

        result.append(headers.get('content-md5'))
        result.append(self._disposition(headers.get('content-disposition')))
        result.append(headers.get('content-language'))
        result.append(headers.get('content-location'))

        return result

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

          1. body MD5

             A string giving the body MD5 value as defined in [MD5].

          2. body disposition

             A parenthesized list with the same content and function as
             the body disposition for a multipart body part.

          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