docs: function(dx, dy) {
          var previousIndex = this.getCurrentPointIndex() - 1;
          var p0 = this.line.geometry.components[previousIndex];
          if (p0 && !isNaN(p0.x) && !isNaN(p0.y)) {
              this.insertXY(p0.x + dx, p0.y + dy);
          }
      }