HTML5 script element - async attribute - when (and how best) to use?

Can you confirm my understanding of HTML5's <script async> attribute?

• Any libraries referenced by other code in the page should not specify the async attribute.
  
  

For example, my script references might appropriately look like:

<script src="jquery..." />         <!-- async not used - ensure that this is loaded before JQuery UI and my code -->

<script src="jquery.ui..." />      <!-- async not used - ensure that this is loaded before my code -->

<script src="my_code1.js" async /> <!-- async used, for page load performance -->

<script src="my_code2.js" async /> <!-- async used, for page load performance -->

• For any code in a $(document).ready(function () { } block, I can be assured that all async script have already loaded.
  
  

Do I have this right?

Source: Tips4all