a printing element having {TAIL ~ an impacting surface} at its front end and {HEAD ~ a driven surface} at its rear end 
a printing element having { TAIL ~ an impacting surface } at its front end and { HEAD ~ a driven surface } at its rear end
OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH