Now I want to break the document per page, reconstructing the structure
So in a first step, I want to isolate the pagebreak to the highest level

<book>
<title>...</title>
<section>
<para>aaa<pb/>bbb</para>
</section>
</book>

<book>
<title>...</title>
<section>
<para>aaa</para>
</section>
<pb/>
<section>
<para>bbb</para>
</section>
</book>

Bearing in mind I need a generic solution
and pagebreaks can happen at every level

Any thoughts?
I am not looking for code, just curious on how people would attack this