I have no idea what this means, but I hope, in time, it will make sense

I am noting it here for future reference.

> is there a way to clean up the callback registry, or to unregister some
> callbacks?

With the model of Seaside, it is hard to tell what callbacks are still
used when doing AJAX. Therefore I suggest to do a full refresh from
time to time.

Note that you can easily do a full refresh through AJAX. Just trigger
an AJAX request to a normal callback, extract the string between
body and /body and place it into the DOM tree. This recreates all
the callbacks in the page and ensures that old ones eventually expire.
To the outside this "full request" feels like a normal AJAX action,
just that it is maybe a bit slower than the other ones.

Actually I planned to write a blog entry about this technique, just
didn't find the time yet.