The DNS Manager form for editing SRV records will choose the domain name automatically. However, I want to add SRV records for a subdomain. For example, I want:

xmpp.example.com. IN A 1.2.3.4
_xmpp-server._tcp.jabber.example.com. IN SRV 10 5 5269 xmpp.example.com

What is the best way to do this? The documentation says to use A records to define subdomains.

I suppose, based on how the UI restricts what you can enter, that you would have to create a separate zone for jabber.example.com where you can add an SRV record for _xmpp-server, protocol tcp, etc, etc.