What is invalid region in Android?
<p>Under "How Android Draws Views" topic, there is such a sentence :</p>

<blockquote>
  <p>Drawing begins with the root node of
  the layout. It is requested to measure
  and draw the layout tree. Drawing is
  handled by walking the tree and
  rendering each View that intersects
  the <strong>invalid region</strong>.</p>
</blockquote>

<p>And I didn't quite understand the term "invalid region".</p>

<p>Here is the <a href="http://developer.android.com/guide/topics/ui/how-android-draws.html" rel="nofollow">source article of the quotation</a>.</p>

<p>Can someone elaborate it?</p>

<p>Thanks.</p>
