title: Unknown attribute android:fullBackupContent
body: <p>I am trying to implement the backup functionality for my app, but I am running into the following problem:</p>
  
  <ul>
  <li>android studio tells me to set the <code>android:fullBackupContent</code> attribute</li>
  <li>when I set this it tells me that the attribute is not recognized</li>
  </ul>
  
  <p>Here is how I have done above in the manifest xml file:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;manifest xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:tools="http://schemas.android.com/tools"
      package="com.balla.popoint"&gt;
      &lt;application
          android:allowBackup="true"
          android:fullBackupContent="@res/xml/backup_rules.xml"
          android:icon="@mipmap/app_icon"
          android:label="@string/app_name"
          android:theme="@style/PoPointTheme"
          tools:ignore="GoogleAppIndexingWarning"&gt;
  </code></pre>
  
  <p>This is how the backup_rules.xml file looks like:</p>
  
  <pre><code>&lt;full-backup-content&gt;
      &lt;include domain="sharedpref" path="."/&gt;
      &lt;include domain="root" path="./somefilename"/&gt;
  &lt;/full-backup-content&gt;`
  </code></pre>
  
  <p>The warning that I get is this:</p>
  
  <blockquote>
  <pre><code>Unknown attribute android:fullBackupContent
  Inspection info: This inspection highlights unknown XML attributes in Android resource files and AndroidManifest.xml
  </code></pre>
  </blockquote>
  
  <p>Why is this warning displayed? What am I doing wrong?</p>