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// Sort credits post type archive by credit year
add_action('pre_get_posts','child_alter_credits_archive_query');
function child_alter_credits_archive_query( $query ) {
    if( $query->is_main_query() && is_post_type_archive('credits') ) {
		$query->set( 'meta_key', 'credit_year' );
	    	$query->set( 'orderby', 'meta_value_num' );
	    	$query->set( 'order', 'DESC' );
    }
}