Nan Xiao's questions

我正在阅读RFC5077，并遇到下图：

        ClientHello
        (empty SessionTicket extension)-------->
                                                         ServerHello
                                     (empty SessionTicket extension)
                                                        Certificate*
                                                  ServerKeyExchange*
                                                 CertificateRequest*
                                      <--------      ServerHelloDone
         Certificate*
         ClientKeyExchange
         CertificateVerify*
         [ChangeCipherSpec]
         Finished                     -------->
                                                    NewSessionTicket
                                                  [ChangeCipherSpec]
                                      <--------             Finished
         Application Data             <------->     Application Data

我猜Certificate*这意味着可以有一个或多个Certificate，并且[ChangeCipherSpec]意味着它是可选的。但我在本文档或 Internet 中找不到准确的定义。我在哪里可以找到对 RFC 的这些符号的解释？