[development] Why Drupal 4.7 is late? (long)

[Robrecht Jacques]

> But there are good things also -- because fixing all this stuff took this
> long, the upgrade system could run its course and got commited on December
> 6. It's also a very good thing, now modules can use the upgrade system.

Where can I find some docs of this upgrade system? I don't find it in
the developers handbook.

Thanks,
Robrecht