The movement implementation uses a key-frame approach. The user indicates where an instance is at a number of given times. DIRSIG then linearly interpolates between the supplied times to generate any additional positioning information needed.
More specifically, the user supplies an initial position and time. Separately in the same file, the user then specifies a series of delta offsets (time, translation, scale, rotation). By using deltas, it becomes easy to shift the absolute time at which a movement occurs.