title: Flutter Firestore: specific documents from a collection (Firestore.collection.where)
body: <p>I am using Firebase Cloud Firestore, and I want to pick specific documents from a collection. I want to call documents whose <code>permission</code> field is 'everyone' or 'groupA'.</p>
  
  <pre><code>stream: Firestore.instance
      .collection('Posts')
      .orderBy('date')
      .where('permission', isEqualTo: 'everyone')
      .where('permission', isEqualTo: 'groupA')
      .snapshot(),
  </code></pre>
  
  <p>I tried this but it is trying to bring me the intersection. I also tried:</p>
  
  <pre><code>    .where('permission', arrayContains: 'everyone')
      .where('permission', arrayContains: 'groupA')
  </code></pre>
  
  <p>But this gives me errors.</p>