This .NET class wraps the ObjectARX enum AcGiVisualStyleProperties.DisplayShadowType. 

It describes the type of shadow to enable.

Public Enum VSDisplayShadowType
  None
  GroundPlane
  Full
  FullAndGround
End Enum

public enum VSDisplayShadowType {
  None,
  GroundPlane,
  Full,
  FullAndGround
}