title: Are changes in sub-collections are supposed to trigger onWrite function or not?
body: <p>Can Firebase functions be triggered by a change in <code>subcollections</code> when the function is listening to a top level document? If not, what does the first line in the wildcard examples of the <a href="https://firebase.google.com/docs/firestore/extend-with-functions" rel="nofollow noreferrer">documentation</a> mean?</p>
  
  <p><strong>What does this mean??? if a sub-collection changes would it trigger the function? 
  But it doesn't seem to and somewhere else in the same page says that too.</strong></p>
  
  <pre><code>// Listen for changes in all documents and all sub-collections
  </code></pre>
  
  <p>...</p>
  
  <pre><code>exports.useWildcard = functions.firestore
    .document('users/{userId}')
    .onWrite((event) =&gt; {
      // If we set `/users/marie` to {name: "marie"} then
      event.params.userId == "marie"
      // ... and ...
      event.data.data() == {name: "Marie"}
    });
  </code></pre>
  
  <p><strong>What is the intended behavior for Firestore and function triggers</strong>?</p>