In an effort to keep track of some of the lesser seen patches to the core of PHP, the Zend Developer Zone has started a weekly summary that talks about the PAT directory:

The PAT directory contains patches (fixes and improvements for the C source code behind PHP) that have been sent to the internal developers' mailing list by members of the wider PHP community. The mailing list is fairly busy - as are the developers - and patches aren't always noticed by someone able to review and perhaps apply them; this can lead to people repeatedly mailing the same patch to the list in the belief that they're being ignored!

The idea behind the posts is to provide a listing of those patches for those looking for them (including the PHP dev team) until they've been evaluated and moved out of the PAT directory purgatory.