Either it's easy and your post #4 is a lie, or it's not so easy and your post #6 is an unjustified ad-hominem attack. Make up your mind.
I was hinting at Joel Spolsky's Law of Leaky Abstractions (
http://www.joelonsoftware.com/articl...tractions.html). When you have to dig around 8-9 different files / classes to reach the bottom of a simple feature (the place where the core of that feature is actually implemented) it's likely that there is a bit of over-abstracting going on. And it's also rational for anyone not to waste time again trying to reverse-engineer the convoluted design of calibre.
Since the problem is so clear to you, you could have said "look at source /path/to/x.py". Why should someone else waste time tracking down something that you know off the top of your head? Software doesn't need to read like a puzzle.