The first part is an ability to set several shape points (like WG's poly selection) in CW or CCW order.

The second is to create shape by defining several subshapes and combining them with AND/OR/XOR/NOT/() operators. For e.g.: square shape [from -1000;-1000 to 1000;0] AND square shape [from -1000;-1000 to 0;1000]. Dynmap can show all subshapes (named) at the same time, no need to calculate exact final border.