def set_ctype(self, ctype, orig_ctype=None):
        """
        Set the selected content type.  Will not override the value of
        the content type if that has already been determined.

        :param ctype: The content type string to set.

        :param orig_ctype: The original content type, as found in the
                           configuration.
        """

        if self.ctype is None:
            self.ctype = ctype
            self.orig_ctype = orig_ctype