wp_ajax_add_tag()

function wp_ajax_add_tag() {
	check_ajax_referer( 'add-tag', '_wpnonce_add-tag' );
	$taxonomy = !empty($_POST['taxonomy']) ? $_POST['taxonomy'] : 'post_tag';
	$tax = get_taxonomy($taxonomy);

	if ( !current_user_can( $tax->cap->edit_terms ) )
		wp_die( -1 );

	$x = new WP_Ajax_Response();

	$tag = wp_insert_term($_POST['tag-name'], $taxonomy, $_POST );

	if ( !$tag || is_wp_error($tag) || (!$tag = get_term( $tag['term_id'], $taxonomy )) ) {
		$message = __('An error has occurred. Please reload the page and try again.');
		if ( is_wp_error($tag) && $tag->get_error_message() )
			$message = $tag->get_error_message();

		$x->add( array(
			'what' => 'taxonomy',
			'data' => new WP_Error('error', $message )
		) );
		$x->send();
	}

	$wp_list_table = _get_list_table( 'WP_Terms_List_Table', array( 'screen' => $_POST['screen'] ) );

	$level = 0;
	if ( is_taxonomy_hierarchical($taxonomy) ) {
		$level = count( get_ancestors( $tag->term_id, $taxonomy, 'taxonomy' ) );
		ob_start();
		$wp_list_table->single_row( $tag, $level );
		$noparents = ob_get_clean();
	}

	ob_start();
	$wp_list_table->single_row( $tag );
	$parents = ob_get_clean();

	$x->add( array(
		'what' => 'taxonomy',
		'supplemental' => compact('parents', 'noparents')
	) );
	$x->add( array(
		'what' => 'term',
		'position' => $level,
		'supplemental' => (array) $tag
	) );
	$x->send();
}