The backframe is configured by interlinked linkages such that the backframe can be locked in {HEAD ~ a fully extended position} in {TAIL ~ use}, or be collapsible when not in use in a way that the overall dimension of the collapsible backframe is smaller than the fully extended backframe 
The backframe is configured by interlinked linkages such that the backframe can be locked in { HEAD ~ a fully extended position } in { TAIL ~ use } , or be collapsible when not in use in a way that the overall dimension of the collapsible backframe is smaller than the fully extended backframe
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD 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 OTH OTH OTH OTH OTH OTH