[JRF => testers] Check if the extra actions below would run into problems if an option
	 *       is updated early on and if so, change the call to schedule these for a later action on add/update
	 *       instead of running them straight away.
	 */
	protected function __construct() {
		parent::__construct();

		/**
		 * Filter: 'wpseo_enable_tracking' - Enables the data tracking of Yoast SEO Premium.
		 *
		 * @api string $is_enabled The enabled state. Default is false.
		 */
		$this->defaults['tracking'] = apply_filters( 'wpseo_enable_tracking', false );

		/* Clear the cache on update/add. */
		add_action( 'add_option_' . $this->option_name, [ 'WPSEO_Utils', 'clear_cache' ] );
		add_action( 'update_option_' . $this->option_name, [ 'WPSEO_Utils', 'clear_cache' ] );

		add_filter( 'admin_title', [ 'Yoast_Input_Validation', 'add_yoast_admin_document_title_errors' ] );

		/**
		 * Filter the `wpseo` option defaults.
		 *
		 * @param array $defaults Array the defaults for the `wpseo` option attributes.
		 */
		$this->defaults = apply_filters( 'wpseo_option_wpseo_defaults', $this->defaults );
	}

	/**
	 * Get the singleton instance of this class.
	 *
	 * @return object
	 */
	public static function get_instance() {
		if ( ! ( self::$instance instanceof self ) ) {
			self::$instance = new self();
		}

		return self::$instance;
	}

	/**
	 * Add filters to make sure that the option is merged with its defaults before being returned.
	 *
	 * @return void
	 */
	public function add_option_filters() {
		parent::add_option_filters();

		list( $hookname, $callback, $priority ) = $this->get_verify_features_option_filter_hook();

		if ( has_filter( $hookname, $callback ) === false ) {
			add_filter( $hookname, $callback, $priority );
		}
	}

	/**
	 * Remove the option filters.
	 * Called from the clean_up methods to make sure we retrieve the original old option.
	 *
	 * @return void
	 */
	public function remove_option_filters() {
		parent::remove_option_filters();

		list( $hookname, $callback, $priority ) = $this->get_verify_features_option_filter_hook();

		remove_filter( $hookname, $callback, $priority );
	}

	/**
	 * Add filters to make sure that the option default is returned if the option is not set.
	 *
	 * @return void
	 */
	public function add_default_filters() {
		parent::add_default_filters();

		list( $hookname, $callback, $priority ) = $this->get_verify_features_default_option_filter_hook();

		if ( has_filter( $hookname, $callback ) === false ) {
			add_filter( $hookname, $callback, $priority );
		}
	}

	/**
	 * Remove the default filters.
	 * Called from the validate() method to prevent failure to add new options.
	 *
	 * @return void
	 */
	public function remove_default_filters() {
		parent::remove_default_filters();

		list( $hookname, $callback, $priority ) = $this->get_verify_features_default_option_filter_hook();

		remove_filter( $hookname, $callback, $priority );
	}

	/**
	 * Validate the option.
	 *
	 * @param array $dirty New value for the option.
	 * @param array $clean Clean value for the option, normally the defaults.
	 * @param array $old   Old value of the option.
	 *
	 * @return array Validated clean value for the option to be saved to the database.
	 */
	protected function validate_option( $dirty, $clean, $old ) {

		foreach ( $clean as $key => $value ) {
			switch ( $key ) {
				case 'version':
					$clean[ $key ] = WPSEO_VERSION;
					break;
				case 'previous_version':
				case 'semrush_country_code':
				case 'license_server_version':
				case 'home_url':
				case 'zapier_api_key':
					if ( isset( $dirty[ $key ] ) ) {
						$clean[ $key ] = $dirty[ $key ];
					}
					break;
				case 'indexing_reason':
					if ( isset( $dirty[ $key ] ) ) {
						$clean[ $key ] = sanitize_text_field( $dirty[ $key ] );
					}
					break;

				/* Verification strings. */
				case 'baiduverify':
				case 'googleverify':
				case 'msverify':
				case 'yandexverify':
					$this->validate_verification_string( $key, $dirty, $old, $clean );
					break;

				/*
				 * Boolean dismiss warnings - not fields - may not be in form
				 * (and don't need to be either as long as the default is false).
				 */
				case 'ignore_search_engines_discouraged_notice':
				case 'ms_defaults_set':
					if ( isset( $dirty[ $key ] ) ) {
						$clean[ $key ] = WPSEO_Utils::validate_bool( $dirty[ $key ] );
					}
					elseif ( isset( $old[ $key ] ) ) {
						$clean[ $key ] = WPSEO_Utils::validate_bool( $old[ $key ] );
					}
					break;

				case 'site_type':
					$clean[ $key ] = $old[ $key ];
					if ( isset( $dirty[ $key ] ) && in_array( $dirty[ $key ], $this->site_types, true ) ) {
						$clean[ $key ] = $dirty[ $key ];
					}
					break;

				case 'environment_type':
					$clean[ $key ] = $old[ $key ];
					if ( isset( $dirty[ $key ] ) && in_array( $dirty[ $key ], $this->environment_types, true ) ) {
						$clean[ $key ] = $dirty[ $key ];
					}
					break;

				case 'has_multiple_authors':
					$clean[ $key ] = $old[ $key ];
					if ( isset( $dirty[ $key ] ) && in_array( $dirty[ $key ], $this->has_multiple_authors_options, true ) ) {
						$clean[ $key ] = $dirty[ $key ];
					}

					break;

				case 'first_activated_on':
				case 'indexing_started':
					$clean[ $key ] = false;
					if ( isset( $dirty[ $key ] ) ) {
						if ( $dirty[ $key ] === false || WPSEO_Utils::validate_int( $dirty[ $key ] ) ) {
							$clean[ $key ] = $dirty[ $key ];
						}
					}
					break;

				case 'tracking':
					$clean[ $key ] = ( isset( $dirty[ $key ] ) ? WPSEO_Utils::validate_bool( $dirty[ $key ] ) : null );
					break;

				case 'myyoast_oauth':
				case 'semrush_tokens':
				case 'custom_taxonomy_slugs':
				case 'zapier_subscription':
					$clean[ $key ] = $old[ $key ];

					if ( isset( $dirty[ $key ] ) ) {
						$items = $dirty[ $key ];
						if ( ! is_array( $items ) ) {
							$items = json_decode( $dirty[ $key ], true );
						}

						if ( is_array( $items ) ) {
							$clean[ $key ] = $dirty[ $key ];
						}
					}

					break;

				case 'permalink_structure':
				case 'category_base_url':
				case 'tag_base_url':
					if ( isset( $dirty[ $key ] ) ) {
						$clean[ $key ] = sanitize_option( $key, $dirty[ $key ] );
					}
					break;

				/*
				 * Boolean (checkbox) fields.
				 */

				/*
				 * Covers:
				 *  'disableadvanced_meta'
				 *  'enable_headless_rest_endpoints'
				 *  'yoast_tracking'
				 *  'dynamic_permalinks'
				 *  'indexing_first_time'
				 *  and most of the feature variables.
				 */
				default:
					$clean[ $key ] = ( isset( $dirty[ $key ] ) ? WPSEO_Utils::validate_bool( $dirty[ $key ] ) : false );
					break;
			}
		}

		return $clean;
	}

	/**
	 * Verifies that the feature variables are turned off if the network is configured so.
	 *
	 * @param mixed $options Value of the option to be returned. Typically an array.
	 *
	 * @return mixed Filtered $options value.
	 */
	public function verify_features_against_network( $options = [] ) {
		if ( ! is_array( $options ) || empty( $options ) ) {
			return $options;
		}

		// For the feature variables, set their values to off in case they are disabled.
		$feature_vars = [
			'disableadvanced_meta'           => false,
			'ryte_indexability'              => false,
			'content_analysis_active'        => false,
			'keyword_analysis_active'        => false,
			'enable_admin_bar_menu'          => false,
			'enable_cornerstone_content'     => false,
			'enable_xml_sitemap'             => false,
			'enable_text_link_counter'       => false,
			'enable_metabox_insights'        => false,
			'enable_link_suggestions'        => false,
			'enable_headless_rest_endpoints' => false,
			'tracking'                       => false,
			'enable_enhanced_slack_sharing'  => false,
			'semrush_integration_active'     => false,
			'zapier_integration_active'      => false,
		];

		// We can reuse this logic from the base class with the above defaults to parse with the correct feature values.
		$options = $this->prevent_disabled_options_update( $options, $feature_vars );

		return $options;
	}

	/**
	 * Gets the filter hook name and callback for adjusting the retrieved option value
	 * against the network-allowed features.
	 *
	 * @return array Array where the first item is the hook name, the second is the hook callback,
	 *               and the third is the hook priority.
	 */
	protected function get_verify_features_option_filter_hook() {
		return [
			"option_{$this->option_name}",
			[ $this, 'verify_features_against_network' ],
			11,
		];
	}

	/**
	 * Gets the filter hook name and callback for adjusting the default option value against the network-allowed features.
	 *
	 * @return array Array where the first item is the hook name, the second is the hook callback,
	 *               and the third is the hook priority.
	 */
	protected function get_verify_features_default_option_filter_hook() {
		return [
			"default_option_{$this->option_name}",
			[ $this, 'verify_features_against_network' ],
			11,
		];
	}

	/**
	 * Clean a given option value.
	 *
	 * @param array  $option_value          Old (not merged with defaults or filtered) option value to
	 *                                      clean according to the rules for this option.
	 * @param string $current_version       Optional. Version from which to upgrade, if not set,
	 *                                      version specific upgrades will be disregarded.
	 * @param array  $all_old_option_values Optional. Only used when importing old options to have
	 *                                      access to the real old values, in contrast to the saved ones.
	 *
	 * @return array Cleaned option.
	 */
	protected function clean_option( $option_value, $current_version = null, $all_old_option_values = null ) {
		// Deal with value change from text string to boolean.
		$value_change = [
			'ignore_search_engines_discouraged_notice',
		];

		$target_values = [
			'ignore',
			'done',
		];

		foreach ( $value_change as $key ) {
			if ( isset( $option_value[ $key ] )
				&& in_array( $option_value[ $key ], $target_values, true )
			) {
				$option_value[ $key ] = true;
			}
		}

		return $option_value;
	}
}