function onPageVisibilityChange( event ) {

		// If, after clicking a link or similar and we're coming back,
		// focus the document.body to ensure we can use keyboard shortcuts
		if( document.hidden === false && document.activeElement !== document.body ) {
			// Not all elements support .blur() - SVGs among them.
			if( typeof document.activeElement.blur === 'function' ) {
				document.activeElement.blur();
			}
			document.body.focus();
		}

	}
Handle for the window level 'visibilitychange' event.

@param {object} [event]