apply_filters( 'post_gallery', string $output, array $attr, int $instance )

2697	 * @see gallery_shortcode()2698	 *2699	 * @param string $output   The gallery output. Default empty.2700	 * @param array  $attr     Attributes of the gallery shortcode.2701	 * @param int    $instance Unique numeric ID of this gallery shortcode instance.2702	 */2703	$output = apply_filters( 'post_gallery', '', $attr, $instance );2704 2705	if ( ! empty( $output ) ) {2706		return $output;2707	}2708 2709	$html5 = current_theme_supports( 'html5', 'gallery' );