There are three combinations of defer and async (see http://www.w3schools.com/tags/att_script_defer.asp):
* $defer false, $async true: The script is executed asynchronously with the rest of the page
(the script will be executed while the page continues the parsing)
* $defer true, $async false: The script is executed when the page has finished parsing.
* $defer false, $async false. (default) The script is loaded and executed immediately. When it finishes
loading the browser continues parsing the rest of the page.
When you are using $defer = true there is no guarantee about the load order of the scripts. Whichever
script loads first will be executed first. The order they appear on the page is completely irrelevant.