Background { 
      eventIn      SFBool   set_bind
      exposedField MFFloat  groundAngle  []            # [0,/2]
      exposedfield MFColor  groundColor  []            # [0,1]
      exposedField MFString backUrl      []
      exposedField MFString bottomUrl    []
      exposedField MFString frontUrl     []
      exposedField MFString leftUrl      []
      exposedField MFString rightUrl     []
      exposedField MFString topUrl       []
      exposedField MFFloat  skyAngle     []            # [0,]
      exposedField MFColor  skyColor     [ 0 0 0 ]     # [0,1]
      eventOut     SFBool   isBound
    }