function onCanvasBlur( event ) {
    /**
     * Raised when the {@link OpenSeadragon.Viewer#canvas} element loses keyboard focus.
     *
     * @event canvas-blur
     * @memberof OpenSeadragon.Viewer
     * @type {object}
     * @property {OpenSeadragon.Viewer} eventSource - A reference to the Viewer which raised this event.
     * @property {OpenSeadragon.MouseTracker} tracker - A reference to the MouseTracker which originated this event.
     * @property {Object} originalEvent - The original DOM event.
     * @property {?Object} userData - Arbitrary subscriber-defined object.
     */
    this.raiseEvent( 'canvas-blur', {
        tracker: event.eventSource,
        originalEvent: event.originalEvent
    });
}
Raised when the {@link OpenSeadragon.Viewer#canvas} element gets keyboard focus.

@event canvas-focus
@memberof OpenSeadragon.Viewer
@type {object}
@property {OpenSeadragon.Viewer} eventSource - A reference to the Viewer which raised this event.
@property {OpenSeadragon.MouseTracker} tracker - A reference to the MouseTracker which originated this event.
@property {Object} originalEvent - The original DOM event.
@property {?Object} userData - Arbitrary subscriber-defined object.