code: function dotProduct(v) {
           return this._x * v.x + this._y * v.y + this._z * (v.z || 1);
         }
docs: return the dot product of this vector and the passed one
  @name dotProduct
  @memberOf me.ObservableVector3d
  @function
  @param {me.Vector2d|me.Vector3d|me.ObservableVector2d|me.ObservableVector3d} v
  @return {Number} The dot product.