Primitives
The lowest level of the object hierarchy contains the primitive objects. Individual
curves or polygons are never stored at the same level as surfaces (i.e. directly under "elements").
Instead, they are always stored at the lowest level in one of the curve sets, either a
projection or cross-section curve set. The curves are usually created with a command such
CURVEÞDesign:Input.
Surfaces also have their basic primitive control curves stored at this level. However, they are
never manipulated directly from the object window. They are only ever manipulated with higher-level
commands without directly dealing with the primitives themselves.