title: Is index important in addView()?
body: <p>I can't understand the function of <code>index</code> in <code>addView(View child, int index)</code> of a <code>ViewGroup</code>.
  What's the <code>index</code> for? Can be <code>index</code> negative value? Does it affect to the <code>layout</code> or the way to display the <code>view</code>?
  I have tested the code with and without <code>index</code> and I can't see the difference. </p>