Anchor

   Anchor { 
      eventIn      MFNode   addChildren
      eventIn      MFNode   removeChildren
      exposedField MFNode   children        []
      exposedField SFString description     "" 
      exposedField MFString parameter       []
      exposedField MFString url             []
      field        SFVec3f  bboxCenter      0 0 0     # (-,)
      field        SFVec3f  bboxSize        -1 -1 -1  # (0,) or -1,-1,-1
    }