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