One note on "Refer Namespace and Class Name": if you have declared a namespace for the current file, you will need to refer to the namespaced class by prefixing it with a namespace separator -- this ensures that the resolution is from the global namespace, and not relative to the current namespace. So, for example:
[geshi lang=php]
namespace Foo;
include 'namespaced-class.php';
$bird1 = new \Christmas\DaysOf\PartridgeInAPearTree();
[/geshi]
Note the "\" preceding "Christmas" -- that's what tells PHP to start at the global namespace.