Billboard {
  eventIn      MFNode   addChildren
  eventIn      MFNode   removeChildren
  exposedField SFVec3f  axisOfRotation  0 1 0
  exposedField MFNode   children        []
  field        SFVec3f  bboxCenter      0 0 0
  field        SFVec3f  bboxSize        -1 -1 -1
}