title: What is the difference between enter/exit and popEnter/popExit animations?
body: <p>In <code>setCustomAnimations()</code> it takes four resource id for the animation. Not really understand them. If someone having clearer picture of it it would be appreciated if you could explain.</p>
  <p>Let's say having fragment A add in the place holder and backstack.</p>
  <pre><code>FragmentTransaction ft = fm.beginTransaction();
          ft.replace(R.id.holder, fragA, FragmentA.FRAGMENT_NAME);
          ft.addToBackStack(FragmentA.FRAGMENT_NAME);
          ft.setCustomAnimations(R.anim.slide_in_from_bottom, R.anim.slide_in_from_top, R.anim.slide_in_from_left, R.anim.slide_in_from_right);
          ft.show(frag);
          ft.commit();
  </code></pre>
  <p>And the replace with fragment B:</p>
  <pre><code>FragmentTransaction ft = fm.beginTransaction();
          ft.replace(R.id.holder, fragB, FragmentB.FRAGMENT_NAME);
          ft.addToBackStack(FragmentB.FRAGMENT_NAME);
          ft.setCustomAnimations(R.anim.slide_in_from_bottom, R.anim.slide_in_from_top, R.anim.slide_in_from_left, R.anim.slide_in_from_right);
          ft.show(frag);
          ft.commit();
  </code></pre>
  <p>next time if do a popstack()</p>
  <pre><code>fm.popBackStackImmediate(FragmentB.FRAGMENT_NAME,
                                  FragmentManager.POP_BACK_STACK_INCLUSIVE);
  </code></pre>
  <p>Which transaction's animation it will be running from?</p>
  <pre><code>/**
   * Set specific animation resources to run for the fragments that are
   * entering and exiting in this transaction. The &lt;code&gt;popEnter&lt;/code&gt;
   * and &lt;code&gt;popExit&lt;/code&gt; animations will be played for enter/exit
   * operations specifically when popping the back stack.
   */
  public abstract FragmentTransaction setCustomAnimations(@AnimRes int enter,
          @AnimRes int exit, @AnimRes int popEnter, @AnimRes int popExit);
  </code></pre>