During Stefan Priebsch' session at the Dutch PHP Conference on PHP 5.3 and PHP 6 - A look ahead a discussion popped up about PHP's namespace support. One of the things that came up is the conflicts that can arise with internal classes.
Take for example this code:
<?php use PEAR::Date::Interval as Interval; ?>
In PHP 5.3 this would alias the class Interval in the namespace PEAR::Date to the class Interval. For now, this code would work just fine. However, if PHP would introduce a class "Interval" at some point in the future (and PHP can do this as it owns the global namespace ) then the above code would suddenly stop working. So in order to use namespaces properly, you always need to have at least two elements left, like:
<?php use PEAR::Date as pd; $interval = new pd::Interval; ?>
You need to make sure of course that the short name that you pick is something that does not sound to much like a class name otherwise you'll have exactly the same issue. It's not very likely that PHP will introduce a class pd though.