Display lists contain zero or more segments.
A segment is an ordered list of zero or more elements.
An element is the stored representation of a Starbase primitive,
attribute or control function or a Starbase Display List function.
There is a one-to-one correspondence between the Starbase function
used to create an element and the element itself.
As mentioned above, the segments of a display list can "call"
other segments; that is, they can be organized in a hierarchical
structure. This multi-level structuring scheme allows construction
of a network of segments that can closely parallel the application
models they represent. You can modify the structure of a segment
network and inquire about many aspects of a segment network.