title: Does a notification message count towards the collapse_key limit?
body: <p>As per the <a href="https://firebase.google.com/docs/cloud-messaging/concept-options#notifications_and_data_messages" rel="nofollow">Firebase Notification docs</a>:</p>
  
  <blockquote>
    <p>Notification messages are always collapsible.</p>
  </blockquote>
  
  <p>I was trying to figure out if they have some intrinsic <code>collapse_key</code>. And if so, does that count towards the <code>collapse_key</code> limit of 4 per device?</p>