[css3-gcpm] maybe-floats vs "in-flow"

css3-gcpm introduces modifiers such as 'snap' or 'unless-room' for the
value of 'float' that can mean that the box isn't actually floated.

I wonder how this should interact with the various bits of CSS that make a
strong distinction between in-flow and out-of-flow boxes.  Some of these
decisions come quite early in the layout process, such as anonymous block
box generation.

The interaction as currently specified is that:

  # An element is called out of flow if it is floated [or ...].
  # An element is called in-flow if it is not out-of-flow.

I haven't thought much about how much of a problem this causes, but I am a
bit nervous about such foundations as initial box tree generation depending
on global layout choices.

I think that the spec should at least draw attention to this sort of
consequence of the float-or-in-flow decision for such a box.

pjrm.