CUPS trigger files for updating ppds attached to queues

["Paul Newall" <p.newalls@ntlworld.com>]

I am using a python ppd updater in the upstream package c2esp and wondering 
if I should change to use the trigger file method that you are using in the 
ubuntu version of c2esp.

I'd like to know:
In which version of cups was the trigger file method first added? (I have 
some users using quite old versions)
Is there any document that explains how to use the trigger file method? - I 
am not quite sure what the contents of the trigger file mean.

Paul Newall