function onCanvasFocus( event ) {

    /**
     * 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.
     */
    this.raiseEvent( 'canvas-focus', {
        tracker: event.eventSource,
        originalEvent: event.originalEvent
    });
}
Raised when a pinch event occurs on the {@link OpenSeadragon.Viewer#canvas} element.

@event canvas-pinch
@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 {String} pointerType - "mouse", "touch", "pen", etc.
@property {Array.<OpenSeadragon.MouseTracker.GesturePoint>} gesturePoints - Gesture points associated with the gesture. Velocity data can be found here.
@property {OpenSeadragon.Point} lastCenter - The previous center point of the two pinch contact points relative to the tracked element.
@property {OpenSeadragon.Point} center - The center point of the two pinch contact points relative to the tracked element.
@property {Number} lastDistance - The previous distance between the two pinch contact points in CSS pixels.
@property {Number} distance - The distance between the two pinch contact points in CSS pixels.
@property {Boolean} shift - True if the shift key was pressed during this event.
@property {Object} originalEvent - The original DOM event.
@property {Boolean} preventDefaultPanAction - Set to true to prevent default pinch to pan behaviour. Default: false.
@property {Boolean} preventDefaultZoomAction - Set to true to prevent default pinch to zoom behaviour. Default: false.
@property {Boolean} preventDefaultRotateAction - Set to true to prevent default pinch to rotate behaviour. Default: false.
@property {?Object} userData - Arbitrary subscriber-defined object.