{HEAD ~ A matrix} of {TAIL ~ apertures} in the front wall are selectively openable and closeable by a controller in response to the orientation of the eraser 
{ HEAD ~ A matrix } of { TAIL ~ apertures } in the front wall are selectively openable and closeable by a controller in response to the orientation of the eraser
HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH