This is great and I like it. One idea based on the other protoxep I just
read would be to change the syntax to:
<muted xmlns='urn:xmpp:mute:0'>
<occupant-id xmlns="urn:xmpp:occupant-id:0"
id="dd72603deec90a38ba552f7c68cbcc61bca202cd" />
</muted>
For better re-use of existing namespaces.