wpdb::has_cap( string $db_cap )

	public function has_cap( $db_cap ) {
		$version = $this->db_version();

		switch ( strtolower( $db_cap ) ) {
			case 'collation' :    // @since WP-2.5.0
			case 'group_concat' : // @since WP-2.7.0
			case 'subqueries' :   // @since WP-2.7.0
				return version_compare( $version, '4.1', '>=' );
			case 'set_charset' :
				return version_compare( $version, '5.0.7', '>=' );
			case 'utf8mb4' :      // @since WP-4.1.0
				if ( version_compare( $version, '5.5.3', '<' ) ) {
					return false;
				}
				if ( $this->use_mysqli ) {
					$client_version = mysqli_get_client_info();
				} else {
					$client_version = mysql_get_client_info();
				}

				/*
				 * libmysql has supported utf8mb4 since 5.5.3, same as the MySQL server.
				 * mysqlnd has supported utf8mb4 since 5.0.9.
				 */
				if ( false !== strpos( $client_version, 'mysqlnd' ) ) {
					$client_version = preg_replace( '/^\D+([\d.]+).*/', '$1', $client_version );
					return version_compare( $client_version, '5.0.9', '>=' );
				} else {
					return version_compare( $client_version, '5.5.3', '>=' );
				}
			case 'utf8mb4_520' : // @since WP-4.6.0
				return version_compare( $version, '5.6', '>=' );
		}

		return false;
	}