t_version = null ) {
		if ( isset( $option_name ) && is_string( $option_name ) && $option_name !== '' ) {
			if ( isset( self::$option_instances[ $option_name ] ) ) {
				self::$option_instances[ $option_name ]->clean( $current_version );
			}
		}
		elseif ( isset( $option_name ) && is_array( $option_name ) && $option_name !== array() ) {
			foreach ( $option_name as $option ) {
				if ( isset( self::$option_instances[ $option ] ) ) {
					self::$option_instances[ $option ]->clean( $current_version );
				}
			}
			unset( $option );
		}
		else {
			foreach ( self::$option_instances as $instance ) {
				$instance->clean( $current_version );
			}
			unset( $instance );

			// If we've done a full clean-up, we can safely remove this really old option.
			delete_option( 'wpseo_indexation' );
		}
	}

	/**
	 * Check that all options exist in the database and add any which don't.
	 *
	 * @return void
	 */
	public static function ensure_options_exist() {
		foreach ( self::$option_instances as $instance ) {
			$instance->maybe_add_option();
		}
	}

	/**
	 * Initialize some options on first install/activate/reset.
	 *
	 * @return void
	 */
	public static function initialize() {
		/* Force WooThemes to use Yoast SEO data. */
		if ( function_exists( 'woo_version_init' ) ) {
			update_option( 'seo_woo_use_third_party_data', 'true' );
		}
	}

	/**
	 * Reset all options to their default values and rerun some tests.
	 *
	 * @return void
	 */
	public static function reset() {
		if ( ! is_multisite() ) {
			$option_names = self::get_option_names();
			if ( is_array( $option_names ) && $option_names !== array() ) {
				foreach ( $option_names as $option_name ) {
					delete_option( $option_name );
					update_option( $option_name, get_option( $option_name ) );
				}
			}
			unset( $option_names );
		}
		else {
			// Reset MS blog based on network default blog setting.
			self::reset_ms_blog( get_current_blog_id() );
		}

		self::initialize();
	}

	/**
	 * Initialize default values for a new multisite blog.
	 *
	 * @param bool $force_init Whether to always do the initialization routine (title/desc test).
	 *
	 * @return void
	 */
	public static function maybe_set_multisite_defaults( $force_init = false ) {
		$option = get_option( 'wpseo' );

		if ( is_multisite() ) {
			if ( $option['ms_defaults_set'] === false ) {
				self::reset_ms_blog( get_current_blog_id() );
				self::initialize();
			}
			elseif ( $force_init === true ) {
				self::initialize();
			}
		}
	}

	/**
	 * Reset all options for a specific multisite blog to their default values based upon a
	 * specified default blog if one was chosen on the network page or the plugin defaults if it was not.
	 *
	 * @param int|string $blog_id Blog id of the blog for which to reset the options.
	 *
	 * @return void
	 */
	public static function reset_ms_blog( $blog_id ) {
		if ( is_multisite() ) {
			$options      = get_site_option( 'wpseo_ms' );
			$option_names = self::get_option_names();

			if ( is_array( $option_names ) && $option_names !== array() ) {
				$base_blog_id = $blog_id;
				if ( $options['defaultblog'] !== '' && $options['defaultblog'] !== 0 ) {
					$base_blog_id = $options['defaultblog'];
				}

				foreach ( $option_names as $option_name ) {
					delete_blog_option( $blog_id, $option_name );

					$new_option = get_blog_option( $base_blog_id, $option_name );

					/* Remove sensitive, theme dependent and site dependent info. */
					if ( isset( self::$option_instances[ $option_name ] ) && self::$option_instances[ $option_name ]->ms_exclude !== array() ) {
						foreach ( self::$option_instances[ $option_name ]->ms_exclude as $key ) {
							unset( $new_option[ $key ] );
						}
					}

					if ( $option_name === 'wpseo' ) {
						$new_option['ms_defaults_set'] = true;
					}

					update_blog_option( $blog_id, $option_name, $new_option );
				}
			}
		}
	}

	/**
	 * Saves the option to the database.
	 *
	 * @param string $wpseo_options_group_name The name for the wpseo option group in the database.
	 * @param string $option_name              The name for the option to set.
	 * @param mixed  $option_value             The value for the option.
	 *
	 * @return boolean Returns true if the option is successfully saved in the database.
	 */
	public static function save_option( $wpseo_options_group_name, $option_name, $option_value ) {
		$options                 = self::get_option( $wpseo_options_group_name );
		$options[ $option_name ] = $option_value;

		if ( isset( self::$option_instances[ $wpseo_options_group_name ] ) && self::$option_instances[ $wpseo_options_group_name ]->multisite_only === true ) {
			self::update_site_option( $wpseo_options_group_name, $options );
		}
		else {
			update_option( $wpseo_options_group_name, $options );
		}

		// Check if everything got saved properly.
		$saved_option = self::get_option( $wpseo_options_group_name );

		return $saved_option[ $option_name ] === $options[ $option_name ];
	}

	/**
	 * Adds the multisite options to the option stack if relevant.
	 *
	 * @param array $option The currently present options settings.
	 *
	 * @return array Options possibly including multisite.
	 */
	protected static function add_ms_option( $option ) {
		if ( ! is_multisite() ) {
			return $option;
		}

		$ms_option = self::get_option( 'wpseo_ms' );

		return array_merge( $option, $ms_option );
	}

	/**
	 * Retrieves a lookup table to find in which option_group a key is stored.
	 *
	 * @return array The lookup table.
	 */
	private static function get_lookup_table() {
		$lookup_table = array();

		self::$backfill->remove_hooks();

		foreach ( array_keys( self::$options ) as $option_name ) {
			$full_option = self::get_option( $option_name );
			foreach ( $full_option as $key => $value ) {
				$lookup_table[ $key ] = $option_name;
			}
		}

		self::$backfill->register_hooks();

		return $lookup_table;
	}

	/**
	 * Retrieves a lookup table to find in which option_group a key is stored.
	 *
	 * @return array The lookup table.
	 */
	private static function get_pattern_table() {
		$pattern_table = array();
		foreach ( self::$options as $option_name => $option_class ) {
			$instance = call_user_func( array( $option_class, 'get_instance' ) );
			foreach ( $instance->get_patterns() as $key ) {
				$pattern_table[ $key ] = $option_name;
			}
		}

		return $pattern_table;
	}

	/* ********************* DEPRECATED METHODS ********************* */

	/**
	 * Correct the inadvertent removal of the fallback to default values from the breadcrumbs.
	 *
	 * @since 1.5.2.3
	 *
	 * @deprecated 7.0
	 * @codeCoverageIgnore
	 */
	public static function bring_back_breadcrumb_defaults() {
		_deprecated_function( __METHOD__, 'WPSEO 7.0' );
	}
}