title: What is the Android GSF package?
body: <p>What is it the GSF_PACKAGE I found in the C2DM Tutorial?<br>
  To be precise: </p>
  
  <pre><code>public static final String GSF_PACKAGE = "com.google.android.gsf"
  </code></pre>
  
  <p>It was used in intent:  </p>
  
  <pre><code>registrationIntent.setPackage(GSF_PACKAGE);
  </code></pre>
  
  <p>On the developers site I found this: </p>
  
  <blockquote>
    <p>"setPackage(String packageName) (Usually optional) Set an explicit
    application package name that limits the components this Intent will
    resolve to."</p>
  </blockquote>
  
  <p>Anyway, what limits and why they might be needed?</p>