According to the sample flex fragmentation algorithm in the spec:

This algorithm assumes that pagination always proceeds only in the forward direction; therefore, in the algorithms below, alignment is mostly ignored prior to pagination. Advanced layout engines may be able to honor alignment across fragments.

In other words, the algorithm suggests performing alignment per fragment in the case of flex. Although the note isn't subscriptive, other algorithms such as grid fragmentation and table fragmentation don't mention a similar suggestion for alignment. Would it make sense to remove this note from the flexbox spec to better match the other algorithms?

Note: neither Gecko or Chromium currently perform flex alignment per fragment.

cc @mstensho @bfgeek