This wrapper is an anonymous closure that provides state throughout the page's lifetime and ensures your code does not unintentionally create/override global variables.
It also explicitly imports the global
jQuery variable so that your code can use the local
$ variable instead of the
jQuery global. This is essential because Drupal loads jQuery with
noConflict() compatibility so the jQuery library does not setup the normal
$ as a global variable.
The wrapper above also explicitly refers to the