> Also, XML is not a good serialization format, and some of the requirements in the protocol are pretty exotic and not trivial to implement in a lot of language

> Also, XML is not a good serialization format, and some of the requirements in the protocol are pretty exotic and not trivial to implement in a lot of languages. Like setting up TLS on an existing connection (plus the absolute refusal of the XMPP WG to allow on-connect TLS). JSON over websocket or HTTP are just better at reaching a wide audience of developers. "StartTLS" behavior is pretty broadly pushed for across the IETF. It usually goes hand in hand with SASL support in protocols like IMAP, SMTP, and XMPP. This is really done for three reasons: 1. Detection via SRV with alternative 'secure' protocol versions requires twice as many DNS lookups 2. It makes it far more likely a client/server will ignore the text on avoiding insecure fallback. 3. It makes it harder for someone who wants to do introspection of traffic to do so cheaply by blocking the standard secure ports. Rather than multiple ports, the trend has been toward requiring TLS now that TLS certificates are something that can often be automated for free. IMHO took considerable push-back to get a cleartext version of HTTP/2 approved.