Group { 
      eventIn      MFNode  addChildren
      eventIn      MFNode  removeChildren
      exposedField MFNode  children       []
      field        SFVec3f bboxCenter     0 0 0     # (-,)
      field        SFVec3f bboxSize       -1 -1 -1  # (0,) or -1,-1,-1
    }