Write-only annotation attribute to silence read fails

[clyfe]

Some endpoints can be write only, for example collecting newsletter emails from public.
It would be nice to mark the corresponding firebase-element as write-only to silence the annoying warning:

FIREBASE WARNING: on() or once() for /emails failed: Error: permission_denied: Client doesn't have permission to access the desired data. 

I'm thinking:

<firebase-element id="emails" write-only
  location="https://myapp.firebaseio.com/emails/">
</firebase-element>