* Sets the proxy selection policy to be used if no [proxy][proxy] is specified explicitly. The
     * proxy selector may return multiple proxies; in that case they will be tried in sequence until
     * a successful connection is established.
     *
     * If unset, the [system-wide default][ProxySelector.getDefault] proxy selector will be used.
     */
    fun proxySelector(proxySelector: ProxySelector) =
      apply {