Following is a structure definition for law extension feature data.
It includes all the input elements to create a law controlled extension
surface.

Minimum four parameters are required to be specified. The base curve, one
of the options in direction reference, length law and angle law are required
for creation of the feature. The law parameters, length_law_parms and
angle_law_parms may be defined using UF_MODL_create_law ( ).

The specification of spine is optional and can be specified at following
three places.
1. Feature spine
2. Length law spine
3. Angle law spine
It is necessary that spine should be unique where ever specified. Only feature
can have spine specified but only law(s) cannot have spine specified.