[css3-fragmentation] Cross-browser consistency

Hello!

I've ben looking on the fragmentation spec for a while and I'm noticing that the UA are sometimes allowed to implement differently the breaking between fragmentainers. Some examples are:

 1.  Breaking the monolithic elements: the UA may overflow or slice the graphical representation
 2.  If the content doesn't fit & there are no possible break points, the UA may break anywhere
 3.  Finding unforced breakpoints when neither of the rules A..D help
 4.  The optimizing unforced breaks guidelines

If I'm a content author writing a publication using regions/columns, I expect that the content will be displayed consistently in all the browsers. Is there a specific reason to leave some of the fragmentation behavior up to the UA to decide?

Thanks,
Andrei.