Antenna House’s margin-break property takes two values, the second controlling whether the block-end margin is kept before the break. This raises some questions:

• Do we want to add independent control over the block-end margin?
• If that second value is omitted (or doesn't exist), is the block-end margin kept or truncated?
• If the block-end margin is kept, this means that it affects the height of an auto-height fragmentainer in which it occurs. If the fragmentainer is fixed-height, does it also mean that the margin should not be truncated, and should force a break earlier in the page in order that it not be truncated?

CC @mstensho @dauwhe @MurakamiShinyu