Class: Container  - X-Ref

Container is a dependency injection container.

It gives access to object instances (services).

Services and parameters are simple key/pair stores.

Parameter and service keys are case insensitive.

A service id can contain lowercased letters, digits, underscores, and dots.
Underscores are used to separate words, and dots to group services
under namespaces:

<ul>
<li>request</li>
<li>mysql_session_storage</li>
<li>symfony.mysql_session_storage</li>
</ul>

A service can also be defined by creating a method named
getXXXService(), where XXX is the camelized version of the id:

<ul>
<li>request -> getRequestService()</li>
<li>mysql_session_storage -> getMysqlSessionStorageService()</li>
<li>symfony.mysql_session_storage -> getSymfony_MysqlSessionStorageService()</li>
</ul>

The container can have three possible behaviors when a service does not exist:

* EXCEPTION_ON_INVALID_REFERENCE: Throws an exception (the default)
* NULL_ON_INVALID_REFERENCE:      Returns null
* IGNORE_ON_INVALID_REFERENCE:    Ignores the wrapping command asking for the reference
(for instance, ignore a setter if the service does not exist)