What is the Apple_PubSub_Socket_Render environment variable for? After running:

env  ; #from with in terminal


I see the following output:

...
Apple_PubSub_Socket_Render=/tmp/launch-pc2V6P/Render
...


What is this environment variable used for? Not really finding anything about what its for and why it is set by default.
PubSub is the backend for how Safari and Mail handle RSS feeds.  There are command line utilities too. From the pubsub man page:


  pubsub -- Utility for managing RSS/Atom subscriptions via the PubSub framework


This variable is just part of that process.  

The ability to read RSS feeds in Safari is going away in Mountain Lion, but I don't know if the entire RSS infrastructure is going away too.