How to implement nested namespace in PHP?

To clear up any confusion regarding different syntax use, namespaces support only two syntaxes, either bracketed or simple-combination both will work. I suggest if you use one over the other, be consistent.

<?php
namespace my\stuff\nested {  // <- bracketed syntax
 class foo {}
}
?>

It creates a class foo inside of the nested namespace with bracketed syntax ({}), it is equivalent to

<?php
namespace my\stuff {  // bracketed syntax but with a nested look
  namespace nested {
     class foo {}
  }
}
?>

You can also use nested namespaces with simple-combination syntax (;)

<?php
namespace mine;
use ultra\long\ns\name;  // <- simple-combination syntax

$a = name\CONSTANT;
name\func();
?>

PHP: FAQ: things you need to know about namespaces