[css3-break] fragments vs boxes (what is a box?)

In CSS 2.1, inline elements are described as splitting into multiple boxes:
http://www.w3.org/TR/CSS2/visuren.html#inline-formatting
I always assumed that therefore each fragment of an inline element had its
own border-box, padding-box, content-box, etc. And therefore at that point
it made sense for CSSOM-VIew to define getClientRects() to return a list of
rectangles, one rectangle per border-box. Each fragment having its own
border-box, padding-box, etc is also very useful for defining how those
fragments are laid out and how they render borders, backgrounds etc.

But I've just realized that the CSS3 Fragments spec talks about elements
--- including inline elements --- having a single 'box' that breaks into
multiple 'fragments'. So here are a couple of questions that need
clarification:
-- Does each fragment have its own border-box, padding-box, etc? If so,
does it make sense for a spec to talk about "an element's border-boxes",
meaning the border-boxes of its fragments? If not, how are we to describe
the equivalent of the border-box of each fragment (the rectangle that's the
outside edge of the border of the fragment)?
-- Should we really be talking about a 'box' consisting of multiple
fragments? To me a 'box' suggests something rectangular, not something
whose geometry is a list of rectangles. If the answer is nevertheless "yes"
then we need to indicate, probably in CSS3 Fragments, that the splitting of
boxes described in CSS 2.1 is obsolete terminology. We would also need to
eliminate all references to 'CSS boxes' that expect them to have
rectangular geometry.

Rob
-- 
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