code: function() {
          var topLeft = this.getTopLeft();
          var topRight = this.getTopRight();
          var bottomLeft = this.getBottomLeft();
          var bottomRight = this.getBottomRight();
          return [[topLeft, topRight],
              [topRight, bottomRight],
              [bottomRight, bottomLeft],
              [bottomLeft, topLeft]];
      }
docs: private