WP_Widget_Text::update( array $new_instance, array $old_instance )

	public function update( $new_instance, $old_instance ) {
		$new_instance = wp_parse_args( $new_instance, array(
			'title' => '',
			'text' => '',
			'filter' => false, // For back-compat.
			'visual' => null, // Must be explicitly defined.
		) );

		$instance = $old_instance;

		$instance['title'] = sanitize_text_field( $new_instance['title'] );
		if ( current_user_can( 'unfiltered_html' ) ) {
			$instance['text'] = $new_instance['text'];
		} else {
			$instance['text'] = wp_kses_post( $new_instance['text'] );
		}

		$instance['filter'] = ! empty( $new_instance['filter'] );

		// Upgrade 4.8.0 format.
		if ( isset( $old_instance['filter'] ) && 'content' === $old_instance['filter'] ) {
			$instance['visual'] = true;
		}
		if ( 'content' === $new_instance['filter'] ) {
			$instance['visual'] = true;
		}

		if ( isset( $new_instance['visual'] ) ) {
			$instance['visual'] = ! empty( $new_instance['visual'] );
		}

		// Filter is always true in visual mode.
		if ( ! empty( $instance['visual'] ) ) {
			$instance['filter'] = true;
		}

		return $instance;
	}