def _write_superbox(self, fptr, box_id):
<EOL>orig_pos = fptr.tell()<EOL>fptr.write(struct.pack('<STR_LIT>', <NUM_LIT:0>, box_id))<EOL>for box in self.box:<EOL><INDENT>box.write(fptr)<EOL><DEDENT>end_pos = fptr.tell()<EOL>fptr.seek(orig_pos)<EOL>fptr.write(struct.pack('<STR_LIT>', end_pos - orig_pos))<EOL>fptr.seek(end_pos)<EOL>
Write a superbox.

        Parameters
        ----------
        fptr : file or file object
            Superbox (box of boxes) to be written to this file.
        box_id : bytes
            4-byte sequence that identifies the superbox.