Eric, I have submitted a new version of the patch. Could you please make a review? Nick, it will be interesting to hear your opinion too.

I tried to follow such rules:
1. Explanation should be succinct yet clear
2. It should tell as less as possible about implementation details
3. Minimize necessary changes

It turns out that these goals could be achieved by 
a) simply reshuffling and structuring the existing text to separate the exceptions (classes, etc.) from the general case;
and
b) adding some minor clarifications.

Armin, thank you for the link. It looks like this is a really old discussion.

PS: Unfortunately, the diff after reshuffling of the text looks big and cumbersome, in fact the changes are minimal.