Actually, after re-reading, all that needs to be added is (bolded):

> Topics and channels are *not* configured a priori. Topics are created on first
> use by publishing to the named topic **or by subscribing to a channel on the
> named topic**. Channels are created on first use by subscribing to the named channel.

(and a few other aesthetic changes like dropping commas and changing `Channels and topics` to `Topics and channels`)