Discussing how to spec the alignment of block-level boxes in the presence of floats...
Notes:
- If we have a border-box that avoids floats, then attach the margins to the containing block, calculate float intrusions, and then align in the remaining space.
- Maybe can define it that way for all margins, even without floats? Should still have the visual effect of aligning the margin box within the container.
- Should alignment cause non-BFCs to avoid floats?