partially enables the spine elements 402 and 404 to be coupled together and or relatively stable relative to one another for example fig9 depicts a detailed view of the groove 426 of the first spine element 402 in some examples the groove 426 may be defined by the first portion 410 fig1 depicts a detailed view of the extension 428 of the second spine element 404 in some examples the extension 428 may extend from the first portion 410 referring to fig9 and 10 in practice the extension 428 is to be at least partially positioned in the groove 426 the interaction between the extension 428 and the groove 426 at least partially enables the spine elements 402 and 404 to be relatively stable relative to one another for example fig1 depicts a detailed view of the end 430 of the first spine element 402 the end 430 includes a biasing or locking element or mechanism 1102 the locking element 1102 may be part of the first portion 410 in some examples the locking element 1102 may be biased by a tab not shown formed from the second portion 412 and positioned beneath the locking element 1102 the interaction between the tab and the locking element 1102 may urge the locking element 1102 toward an edge 1104 of the second portion 412 for example in some examples the locking element 1102 includes a tapered surface 1106 and a step 1108 that may facilitate coupling with and or.