A guide 1, wherein said housing unfolds to facilitate installation onto {HEAD ~ said track} at any point along {TAIL ~ the length} of said track 
A guide 1 , wherein said housing unfolds to facilitate installation onto { HEAD ~ said track } at any point along { TAIL ~ the length } of said track
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH