docs: function(visibility) {
          if (visibility != this.visibility) {
              this.visibility = visibility;
              this.display(visibility);
              this.redraw();
              if (this.map != null) {
                  this.map.events.triggerEvent("changelayer", {
                      layer: this,
                      property: "visibility"
                  });
              }
              this.events.triggerEvent("visibilitychanged");
          }
      }