WP_Customize_Setting::_multidimensional_preview_filter( mixed $original )

	final public function _multidimensional_preview_filter( $original ) {
		if ( ! $this->is_current_blog_previewed() ) {
			return $original;
		}

		$id_base = $this->id_data['base'];

		// If no settings have been previewed yet (which should not be the case, since $this is), just pass through the original value.
		if ( empty( self::$aggregated_multidimensionals[ $this->type ][ $id_base ]['previewed_instances'] ) ) {
			return $original;
		}

		foreach ( self::$aggregated_multidimensionals[ $this->type ][ $id_base ]['previewed_instances'] as $previewed_setting ) {
			// Skip applying previewed value for any settings that have already been applied.
			if ( ! empty( self::$aggregated_multidimensionals[ $this->type ][ $id_base ]['preview_applied_instances'][ $previewed_setting->id ] ) ) {
				continue;
			}

			// Do the replacements of the posted/default sub value into the root value.
			$value = $previewed_setting->post_value( $previewed_setting->default );
			$root = self::$aggregated_multidimensionals[ $previewed_setting->type ][ $id_base ]['root_value'];
			$root = $previewed_setting->multidimensional_replace( $root, $previewed_setting->id_data['keys'], $value );
			self::$aggregated_multidimensionals[ $previewed_setting->type ][ $id_base ]['root_value'] = $root;

			// Mark this setting having been applied so that it will be skipped when the filter is called again.
			self::$aggregated_multidimensionals[ $previewed_setting->type ][ $id_base ]['preview_applied_instances'][ $previewed_setting->id ] = true;
		}

		return self::$aggregated_multidimensionals[ $this->type ][ $id_base ]['root_value'];
	}