This page is now obsolete. The proposed processing model is in the specification draft:

http://dev.w3.org/csswg/css3-regions/#regions-visual-formatting-details

and the use cases are in the test repository:

https://hg.csswg.org/test/file/887baeb650dd/contributors/adobe/incoming/css3-regions

(the regions-auto-size-*.xht tests)