An indexing and registration shown is maintained whereby the location of {HEAD ~ any particular container} within {TAIL ~ the entire tiered grouping} of containers is known at all times 
An indexing and registration shown is maintained whereby the location of { HEAD ~ any particular container } within { TAIL ~ the entire tiered grouping } of containers is known at all times
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH