There are a few properties where percentages are resolved against the size of the container. What if the container is fragmented? Each fragment is likely to have a different block size, and could even have different inline-sizes. How are these percentages then resolved? Per fragment? Based on the first fragment? Something else? For instance:

• margin-*, padding-* (both have potentially multiple instances, due to box-decoration-break)
• text-indent
• left, right, top, bottom
• (I'm sure there are more)