6 ) !== 'wpseo_' ) {
			$meta_key = 'wpseo_' . $meta_key;
		}

		self::set_values( $term_id, $taxonomy, [ $meta_key => $meta_value ] );
	}

	/**
	 * Find the keyword usages in the metas for the taxonomies/terms.
	 *
	 * @param string $keyword          The keyword to look for.
	 * @param string $current_term_id  The current term id.
	 * @param string $current_taxonomy The current taxonomy name.
	 *
	 * @return array
	 */
	public static function get_keyword_usage( $keyword, $current_term_id, $current_taxonomy ) {
		$tax_meta = self::get_tax_meta();


		$found = [];
		// @todo Check for terms of all taxonomies, not only the current taxonomy.
		foreach ( $tax_meta as $taxonomy_name => $terms ) {
			foreach ( $terms as $term_id => $meta_values ) {
				$is_current = ( $current_taxonomy === $taxonomy_name && (string) $current_term_id === (string) $term_id );
				if ( ! $is_current && ! empty( $meta_values['wpseo_focuskw'] ) && $meta_values['wpseo_focuskw'] === $keyword ) {
					$found[] = $term_id;
				}
			}
		}

		return [ $keyword => $found ];
	}

	/**
	 * Saving the values for the given term_id.
	 *
	 * @param int    $term_id  ID of the term to save data for.
	 * @param string $taxonomy The taxonomy the term belongs to.
	 * @param array  $clean    Array with clean values.
	 */
	private static function save_clean_values( $term_id, $taxonomy, array $clean ) {
		$tax_meta = self::get_tax_meta();

		/* Add/remove the result to/from the original option value. */
		if ( $clean !== [] ) {
			$tax_meta[ $taxonomy ][ $term_id ] = $clean;
		}
		else {
			unset( $tax_meta[ $taxonomy ][ $term_id ] );
			if ( isset( $tax_meta[ $taxonomy ] ) && $tax_meta[ $taxonomy ] === [] ) {
				unset( $tax_meta[ $taxonomy ] );
			}
		}

		// Prevent complete array validation.
		$tax_meta['wpseo_already_validated'] = true;

		self::save_tax_meta( $tax_meta );
	}

	/**
	 * Getting the meta from the options.
	 *
	 * @return void|array
	 */
	private static function get_tax_meta() {
		return get_option( self::$name );
	}

	/**
	 * Saving the tax meta values to the database.
	 *
	 * @param array $tax_meta Array with the meta values for taxonomy.
	 */
	private static function save_tax_meta( $tax_meta ) {
		update_option( self::$name, $tax_meta );
	}

	/**
	 * Getting the taxonomy meta for the given term_id and taxonomy.
	 *
	 * @param int    $term_id  The id of the term.
	 * @param string $taxonomy Name of the taxonomy to which the term is attached.
	 *
	 * @return array
	 */
	private static function get_term_tax_meta( $term_id, $taxonomy ) {
		$tax_meta = self::get_tax_meta();

		/* If we have data for the term, merge with defaults for complete array, otherwise set defaults. */
		if ( isset( $tax_meta[ $taxonomy ][ $term_id ] ) ) {
			return array_merge( self::$defaults_per_term, $tax_meta[ $taxonomy ][ $term_id ] );
		}

		return self::$defaults_per_term;
	}
}