We allow ancestors to affect leading trimming on descendants, so that common cases like

<div class=warning style="borders and padding and leading-trim">
  <p>This is just a paragraph. Maybe this line is <p>, or not, it could be anything.
</div>

will work for authors. But we don't specify what happens if various ancestors have different values for leading-trim.

Maybe we should do something similar to break-before and switch to an auto/no/yes model where auto does whatever the ancestor says and otherwise the innermost value wins?