README.variables is distributed with 1.2. I notice that all README’s are being replaced by corresponding .txt’s, and indeed there is a variables.txt in the trunk. But nowhere is this to be found in Asterisk 1.4.x releases. Is this a bug or am I missing something?
Oops 
Is channelvariables.txt - just got answer from Mentis.
Don’t feel bad. I missed that one as well. Digium is just trying to make sure we’re paying attention. 