Event reference
domattributenamechanged mutationnameevent dom l3 removed the name of an attribute changed (use mutation observers instead).
... domelementnamechanged mutationnameevent dom l3 removed the name of an element changed (use mutation observers instead).

MutationEvent - Web APIs
}, false); the event object is passed to the listener in a mutationevent (see its definition in the specification) for most events, and mutationnameevent for domattributenamechanged and domelementnamechanged.

Mutation events - Developer guides
}, false); the event object is passed to the listener in a mutationevent (see its definition in the specification) for most events, and mutationnameevent for domattributenamechanged and domelementnamechanged.