'Write information about uncrossable breaks (non linear items in
the spine.'

def write_uncrossable_breaks(self):

    if (not WRITE_UNCROSSABLE_BREAKS):
        return
    breaks = self.serializer.breaks
    for i in xrange(1, (self.last_text_record_idx + 1)):
        offset = (i * RECORD_SIZE)
        pbreak = 0
        running = offset
        buf = StringIO()
        while (breaks and ((breaks[0] - offset) < RECORD_SIZE)):
            pbreak = ((breaks.pop(0) - running) >> 3)
            encoded = encint(pbreak)
            buf.write(encoded)
            running += (pbreak << 3)
        encoded = encode_trailing_data(buf.getvalue())
        self.records[i] += encoded
