def save(self, filename=None):
        """Save changes to a file.

        If no filename is given, the one most recently loaded is used.

        Tags are always written at the end of the file, and include
        a header and a footer.
        """

        filename = filename or self.filename
        try:
            fileobj = open(filename, "r+b")
        except IOError:
            fileobj = open(filename, "w+b")
        data = _APEv2Data(fileobj)

        if data.is_at_start:
            delete_bytes(fileobj, data.end - data.start, data.start)
        elif data.start is not None:
            fileobj.seek(data.start)
            # Delete an ID3v1 tag if present, too.
            fileobj.truncate()
        fileobj.seek(0, 2)

        # "APE tags items should be sorted ascending by size... This is
        # not a MUST, but STRONGLY recommended. Actually the items should
        # be sorted by importance/byte, but this is not feasible."
        tags = sorted((v._internal(k) for k, v in self.items()), key=len)
        num_tags = len(tags)
        tags = b"".join(tags)

        header = bytearray(b"APETAGEX")
        # version, tag size, item count, flags
        header += struct.pack("<4I", 2000, len(tags) + 32, num_tags,
                              HAS_HEADER | IS_HEADER)
        header += b"\0" * 8
        fileobj.write(header)

        fileobj.write(tags)

        footer = bytearray(b"APETAGEX")
        footer += struct.pack("<4I", 2000, len(tags) + 32, num_tags,
                              HAS_HEADER)
        footer += b"\0" * 8

        fileobj.write(footer)
        fileobj.close()