*
     * The following protocols are currently supported:
     *
     * * [http/1.1][rfc_2616]
     * * [h2][rfc_7540]
     * * [h2 with prior knowledge(cleartext only)][rfc_7540_34]
     *
     * **This is an evolving set.** Future releases include support for transitional
     * protocols. The http/1.1 transport will never be dropped.
     *

    mutual TLS where these roles are reversed.

    These classes make it possible to enable HTTPS in MockWebServer in [just a few lines of
    code][https_server_sample].

 *  **OkHttp now supports prior knowledge cleartext HTTP/2.** Enable this by setting
    `Protocol.H2_PRIOR_KNOWLEDGE` as the lone protocol on an `OkHttpClient.Builder`. This mode
    only supports `http:` URLs and is best suited in closed environments where HTTPS is