can be false if the option doesn't exist).
	 */
	protected function get_original_option() {
		$this->remove_default_filters();
		$this->remove_option_filters();

		// Get (unvalidated) array, NOT merged with defaults.
		if ( $this->multisite_only !== true ) {
			$option_value = get_option( $this->option_name );
		}
		else {
			$option_value = get_site_option( $this->option_name );
		}

		$this->add_option_filters();
		$this->add_default_filters();

		return $option_value;
	}

	/**
	 * Add the option if it doesn't exist for some strange reason.
	 *
	 * @uses WPSEO_Option::get_original_option()
	 *
	 * @return void
	 */
	public function maybe_add_option() {
		if ( $this->get_original_option() === false ) {
			if ( $this->multisite_only !== true ) {
				update_option( $this->option_name, $this->get_defaults() );
			}
			else {
				$this->update_site_option( $this->get_defaults() );
			}
		}
	}

	/**
	 * Update a site_option.
	 *
	 * {@internal This special method is only needed for multisite options, but very needed indeed there.
	 *            The order in which certain functions and hooks are run is different between
	 *            get_option() and get_site_option() which means in practice that the removing
	 *            of the default filters would be done too late and the re-adding of the default
	 *            filters might not be done at all.
	 *            Aka: use the WPSEO_Options::update_site_option() method (which calls this method)
	 *            for safely adding/updating multisite options.}}
	 *
	 * @param mixed $value The new value for the option.
	 *
	 * @return bool Whether the update was succesfull.
	 */
	public function update_site_option( $value ) {
		if ( $this->multisite_only === true && is_multisite() ) {
			$this->remove_default_filters();
			$result = update_site_option( $this->option_name, $value );
			$this->add_default_filters();

			return $result;
		}
		else {
			return false;
		}
	}

	/**
	 * Retrieve the real old value (unmerged with defaults), clean and re-save the option.
	 *
	 * @uses WPSEO_Option::get_original_option()
	 * @uses WPSEO_Option::import()
	 *
	 * @param string|null $current_version Optional. Version from which to upgrade, if not set,
	 *                                     version specific upgrades will be disregarded.
	 *
	 * @return void
	 */
	public function clean( $current_version = null ) {
		$option_value = $this->get_original_option();
		$this->import( $option_value, $current_version );
	}

	/**
	 * Clean and re-save the option.
	 *
	 * @uses clean_option() method from concrete class if it exists.
	 *
	 * @todo [JRF/whomever] Figure out a way to show settings error during/after the upgrade - maybe
	 * something along the lines of:
	 * -> add them to a property in this class
	 * -> if that property isset at the end of the routine and add_settings_error function does not exist,
	 *    save as transient (or update the transient if one already exists)
	 * -> next time an admin is in the WP back-end, show the errors and delete the transient or only delete it
	 *    once the admin has dismissed the message (add ajax function)
	 * Important: all validation routines which add_settings_errors would need to be changed for this to work
	 *
	 * @param array       $option_value          Option value to be imported.
	 * @param string|null $current_version       Optional. Version from which to upgrade, if not set,
	 *                                           version specific upgrades will be disregarded.
	 * @param array|null  $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 void
	 */
	public function import( $option_value, $current_version = null, $all_old_option_values = null ) {
		if ( $option_value === false ) {
			$option_value = $this->get_defaults();
		}
		elseif ( is_array( $option_value ) && method_exists( $this, 'clean_option' ) ) {
			$option_value = $this->clean_option( $option_value, $current_version, $all_old_option_values );
		}

		/*
		 * Save the cleaned value - validation will take care of cleaning out array keys which
		 * should no longer be there.
		 */
		if ( $this->multisite_only !== true ) {
			update_option( $this->option_name, $option_value );
		}
		else {
			$this->update_site_option( $this->option_name, $option_value );
		}
	}

	/**
	 * Returns the variable array key patterns for an options class.
	 *
	 * @return array
	 */
	public function get_patterns() {
		return (array) $this->variable_array_key_patterns;
	}

	/**
	 * Retrieves the option name.
	 *
	 * @return string The set option name.
	 */
	public function get_option_name() {
		return $this->option_name;
	}

	/*
	 * Concrete classes *may* contain a clean_option method which will clean out old/renamed
	 * values within the option.
	 *
	 * ```
	 * abstract public function clean_option( $option_value, $current_version = null, $all_old_option_values = null );
	 * ```
	 */

	/* *********** HELPER METHODS for internal use. *********** */

	/**
	 * Helper method - Combines a fixed array of default values with an options array
	 * while filtering out any keys which are not in the defaults array.
	 *
	 * @todo [JRF] - shouldn't this be a straight array merge ? at the end of the day, the validation
	 * removes any invalid keys on save.
	 *
	 * @param array|null $options Optional. Current options. If not set, the option defaults
	 *                            for the $option_key will be returned.
	 *
	 * @return array Combined and filtered options array.
	 */
	protected function array_filter_merge( $options = null ) {

		$defaults = $this->get_defaults();

		if ( ! isset( $options ) || $options === false || $options === [] ) {
			return $defaults;
		}

		$options = (array) $options;

		/*
			$filtered = array();

			if ( $defaults !== array() ) {
				foreach ( $defaults as $key => $default_value ) {
					// @todo should this walk through array subkeys ?
					$filtered[ $key ] = ( isset( $options[ $key ] ) ? $options[ $key ] : $default_value );
				}
			}
		*/
		$filtered = array_merge( $defaults, $options );

		return $filtered;
	}

	/**
	 * Sets updated values for variables that are disabled via the override option back to their previous values.
	 *
	 * @param array $updated Updated option value.
	 * @param array $old     Old option value.
	 *
	 * @return array Updated option value, with all disabled variables set to their old values.
	 */
	protected function prevent_disabled_options_update( $updated, $old ) {
		$override_option = $this->get_override_option();
		if ( empty( $override_option ) ) {
			return $updated;
		}

		/*
		 * This loop could as well call `is_disabled( $key )` for each iteration,
		 * however this would be worse performance-wise.
		 */
		foreach ( $old as $key => $value ) {
			if ( isset( $override_option[ self::ALLOW_KEY_PREFIX . $key ] ) && ! $override_option[ self::ALLOW_KEY_PREFIX . $key ] ) {
				$updated[ $key ] = $old[ $key ];
			}
		}

		return $updated;
	}

	/**
	 * Retrieves the value of the override option, if available.
	 *
	 * An override option contains values that may determine access to certain sub-variables
	 * of this option.
	 *
	 * Only regular options in multisite can have override options, which in that case
	 * would be network options.
	 *
	 * @return array Override option value, or empty array if unavailable.
	 */
	protected function get_override_option() {
		if ( empty( $this->override_option_name ) || $this->multisite_only === true || ! is_multisite() ) {
			return [];
		}

		return get_site_option( $this->override_option_name, [] );
	}

	/**
	 * Make sure that any set option values relating to post_types and/or taxonomies are retained,
	 * even when that post_type or taxonomy may not yet have been registered.
	 *
	 * {@internal The wpseo_titles concrete class overrules this method. Make sure that any
	 *            changes applied here, also get ported to that version.}}
	 *
	 * @param array $dirty Original option as retrieved from the database.
	 * @param array $clean Filtered option where any options which shouldn't be in our option
	 *                     have already been removed and any options which weren't set
	 *                     have been set to their defaults.
	 *
	 * @return array
	 */
	protected function retain_variable_keys( $dirty, $clean ) {
		if ( ( is_array( $this->variable_array_key_patterns ) && $this->variable_array_key_patterns !== [] ) && ( is_array( $dirty ) && $dirty !== [] ) ) {
			foreach ( $dirty as $key => $value ) {

				// Do nothing if already in filtered options.
				if ( isset( $clean[ $key ] ) ) {
					continue;
				}

				foreach ( $this->variable_array_key_patterns as $pattern ) {

					if ( strpos( $key, $pattern ) === 0 ) {
						$clean[ $key ] = $value;
						break;
					}
				}
			}
		}

		return $clean;
	}

	/**
	 * Check whether a given array key conforms to one of the variable array key patterns for this option.
	 *
	 * @usedby validate_option() methods for options with variable array keys.
	 *
	 * @param string $key Array key to check.
	 *
	 * @return string Pattern if it conforms, original array key if it doesn't or if the option
	 *                does not have variable array keys.
	 */
	protected function get_switch_key( $key ) {
		if ( ! isset( $this->variable_array_key_patterns ) || ( ! is_array( $this->variable_array_key_patterns ) || $this->variable_array_key_patterns === [] ) ) {
			return $key;
		}

		foreach ( $this->variable_array_key_patterns as $pattern ) {
			if ( strpos( $key, $pattern ) === 0 ) {
				return $pattern;
			}
		}

		return $key;
	}
}