Drupal 7 Module Development

Chapter 10
From here onwards, when we want to use the hello world library, we would add it
with the following call:
drupal_add_library('hello_world', 'hello_world_library');
The first argument is the module that defined the library and the second argument is
the key for the library defined.
API documentation about hook_library() is available at
http://api.drupal.org/api/function/hook_library/7.
Altering information in hook_library
Drupal provides a hook_library_alter() function, where modules can intercept
the libraries defined by hook_library() and either act or make changes to them.
A simple example could be another module providing a more recent version
of the hello_world.js script. For the example the module will be called Hello
World Update. In the file hello_world_update.module we have the following
implementation of hook_library_alter():
/**
* Implements hook_library_alter().
*/
function hello_world_library_alter(&$libraries, $module) {
if ($module == 'hello_world' &&
isset($libraries['hello_world_library'])) {
// Verify existing version is older than the one we are
// updating to.
if (version_compare($libraries['hello_world_library']['version'],
'2.0', '