The return is a status or error string, which may be null.
The following keywords can be specified:
Conductor
Routing
GroundPlane
GroundPlaneDark
GroundPlaneClear
TermDefault
Contact
Via
DarkField
Thickness
Rho
Sigma
Rsh
EpsRel
Capacitance
Lambda
Tline
Antenna
The functions in this section provide an interface to the extraction system. This interface is by no means complete, but it allows many common operations to be performed and allows traversal and information retrieval.