[css3-regions] different events, speed boost when using many regions

Hey,
I am currently working on http://BookJS.net where we use CSS Regions to
make book layout. I've been working on this since July, and it relied on
the Webkit implementation of CSS Regions to make everything work.

You can find a current demo of a very simple editor which reflows text and
footnotes here: http://sourcefabric.github.com/BookJS/test.html

Now when documents get longer, things slow down considerably. An important
reason for that is that I have to listen to the regionlayoutupdate event
and then check for everything else manually -- have footnoted moved to
another page, do new pages need to be added (or removed), etc. .

It would therefore be nice to instead have several different events:

-- One event for when a certain node moved from one region to another.
-- One event for when new regions are needed or two many (change on
firstEmptyRegionIndex and/or overset)
-- One event if there is any change to the contents of a given flow, the
way the current regionlayoutupdate event works.

-- 
Johannes Wilm
Booktype Developer
+1 520 399 8880