code: function (alpha) {
              if (typeof (alpha) === "number") {
                  this.alpha = me.Math.clamp(alpha, 0.0, 1.0);
                  // Set to 1 if alpha is NaN
                  if (isNaN(this.alpha)) {
                      this.alpha = 1.0;
                  }
              }
          }
docs: set the renderable alpha channel value<br>
  @name setOpacity
  @memberOf me.Renderable.prototype
  @function
  @param {Number} alpha opacity value between 0.0 and 1.0