use statements provide the ability to refer to an external fully qualified name. Since it will be used to locate definitions in other namespaces and/or files, it is important to check the validity of the fully qualified name.
<?php
namespace X;
use AnotherNamespace\Aclass;
use AnotherNamespace\Subnamespace;
$a = new Aclass();
?>PHP will not check the validity of use at compile time, but at execution time. It will then raise a fatal error.
It is recommended to make sure that use statement are always pointing to an existing definition.
The following patterns are considered warnings:
<?php
namespace X;
use AnotherNamespace\UndefinedClass;
?>