title: What is XML property xmlns:app?
body: <p>XML is working good with:</p>
  
  <pre><code>xmlns:app="http://schemas.android.com/apk/res-auto"
  </code></pre>
  
  <p>but can't see max characters with </p>
  
  <pre><code>xmlns:app="http://schemas.android.com/tools"
  </code></pre>
  
  <p>which is completed by Android Studio auto .</p>
  
  <p>Here is my XML:</p>
  
  <pre><code>&lt;com.rengwuxian.materialedittext.MaterialEditText
      android:id="@+id/remark_text"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:layout_marginLeft="15dp"
      android:layout_marginRight="15dp"
      app:met_maxCharacters="20"
      app:met_baseColor="@color/black"
      app:met_primaryColor="@color/white" /&gt;
  </code></pre>