bkt_new()
instantiates a newbkt
node.bkt_type()
checks if the node is abkt
node.bkt_<child>_get()
returns the<child>
node ofbkt
.bkt_<child>_set()
sets the new<child>
and deletes the old<child>
.bkt_<child>_rep()
sets the new<child>
and returns the old<child>
.