Selection-driven explicit-at rebasing still holds for broader sibling units with multi-block child containers

What happened

After proving sibling complex wrapper-list fragments where each unit had:

and then widening those child containers to multiple blocks, the next honest question was explicit-at rebasing for later sibling units.

The current model still held.

The same selection-driven rule survived:

quote-target inserts can move later sibling units
nested-list-target inserts can leave later sibling units alone
range refs should follow the real post-insert selection semantics for that container

No new rebasing abstraction was needed.

The child containers got internally broader, but the outer sibling unit and the real insert container story did not change.

So the same question still decides the result:

If yes, later sibling units rebase. If not, they do not.

Do not invent a new explicit-at model just because inner child containers got multi-block.

First check whether the real insert-container semantics are unchanged.

If they are, keep following selection truth.