code: function accessibleFocus() {
  	document.addEventListener( 'keydown', function( event ) {
  		if ( keyboardNavigation ) {
  			return;
  		}
  		if ( keyboardNavigationKeycodes.indexOf( event.keyCode ) !== -1 ) {
  			keyboardNavigation = true;
  			document.documentElement.classList.add( 'accessible-focus' );
  		}
  	} );
  	document.addEventListener( 'mouseup', function() {
  		if ( ! keyboardNavigation ) {
  			return;
  		}
  		keyboardNavigation = false;
  		document.documentElement.classList.remove( 'accessible-focus' );
  	} );
  }
docs: keyCodes for tab, space, left, up, right, down respectively