WP_Customize_Nav_Menus::filter_wp_nav_menu_args( array $args )

	public function filter_wp_nav_menu_args( $args ) {
		/*
		 * The following conditions determine whether or not this instance of
		 * wp_nav_menu() can use selective refreshed. A wp_nav_menu() can be
		 * selective refreshed if...
		 */
		$can_partial_refresh = (
			// ...if wp_nav_menu() is directly echoing out the menu (and thus isn't manipulating the string after generated),
			! empty( $args['echo'] )
			&&
			// ...and if the fallback_cb can be serialized to JSON, since it will be included in the placement context data,
			( empty( $args['fallback_cb'] ) || is_string( $args['fallback_cb'] ) )
			&&
			// ...and if the walker can also be serialized to JSON, since it will be included in the placement context data as well,
			( empty( $args['walker'] ) || is_string( $args['walker'] ) )
			// ...and if it has a theme location assigned or an assigned menu to display,
			&& (
				! empty( $args['theme_location'] )
				||
				( ! empty( $args['menu'] ) && ( is_numeric( $args['menu'] ) || is_object( $args['menu'] ) ) )
			)
			&&
			// ...and if the nav menu would be rendered with a wrapper container element (upon which to attach data-* attributes).
			(
				! empty( $args['container'] )
				||
				( isset( $args['items_wrap'] ) && '<' === substr( $args['items_wrap'], 0, 1 ) )
			)
		);
		$args['can_partial_refresh'] = $can_partial_refresh;

		$exported_args = $args;

		// Empty out args which may not be JSON-serializable.
		if ( ! $can_partial_refresh ) {
			$exported_args['fallback_cb'] = '';
			$exported_args['walker'] = '';
		}

		/*
		 * Replace object menu arg with a term_id menu arg, as this exports better
		 * to JS and is easier to compare hashes.
		 */
		if ( ! empty( $exported_args['menu'] ) && is_object( $exported_args['menu'] ) ) {
			$exported_args['menu'] = $exported_args['menu']->term_id;
		}

		ksort( $exported_args );
		$exported_args['args_hmac'] = $this->hash_nav_menu_args( $exported_args );

		$args['customize_preview_nav_menus_args'] = $exported_args;
		$this->preview_nav_menu_instance_args[ $exported_args['args_hmac'] ] = $exported_args;
		return $args;
	}