title: Android Data Binding: how to pass variable to include layout
body: <p>Google documentation says that variables may be passed into an included layout's binding from the containing layout but I can't make it work but get data binding error ****msg:Identifiers must have user defined types from the XML file. handler is missing it. 
  The including XML looks like this:</p>
  
  <pre><code>&lt;layout xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:bind="http://schemas.android.com/apk/res-auto"&gt;
  
  &lt;data&gt;
      &lt;import type="com.example.FocusChangeHandler"/&gt;
  
      &lt;variable
          name="handler"
          type="FocusChangeHandler"/&gt;
  &lt;/data&gt;
  
  &lt;!-- Some other views  ---&gt;
  
     &lt;include
              android:id="@+id/inputs"
              layout="@layout/input_fields"
              bind:handler="@{handler}"/&gt;        
  &lt;/layout&gt;
  </code></pre>
  
  <p>And the included XML like this: </p>
  
  <pre><code>&lt;layout xmlns:android="http://schemas.android.com/apk/res/android"&gt;
  &lt;EditText
     android:id="@+id/nameEdit"       
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"       
     android:onFocusChange="@{handler.onFocusChange}"/&gt;
  &lt;/layout&gt;
  </code></pre>
  
  <p>I'm able to refer the Views from included layout through generated binding class but passing a variable just doesn't work. </p>