Comment by strogonoff

It is unfortunate that you cannot simply move a block of HTML elsewhere where the context is otherwise perfectly suitable but expected heading level is different[0].

Section-relative headings were briefly part of the spec but quickly got removed. As it stands, I would not consider any block of HTML with an <hX> element portable.

[0] https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/...