title: Difference between navigateUp() and popBackStack()
body: <p>I'm creating a simple ToDo app and checking about the Navigation methods to return to my mainFragment from the AddTask Fragment. And I found that I can return using navigateUp() and also popBackStack(), but I don't understand the difference.</p>
  <p>When I use this:</p>
  <pre><code>Navigation.findNavController(it).navigateUp()
  </code></pre>
  <p>Or this:</p>
  <pre><code>Navigation.findNavController(it).popBackStack()
  </code></pre>
  <p>I return to the mainFragment and I think, the addTaskFragment is popped from the stack, so could someone please explain me?</p>