We now have an XHTML document as the child of [t:]tide-data.

We need the second XHTML pre element parsed into [t:]tide-level elements.

Let's focus on the XHTML by limiting the scope to the XHTML html element.

<p:subtree select="t:tide-data/h:html">

...

</p:subtree>

This makes the XHTML html element the document element for the contained steps.

Inside that element we can "project a view" so that only the XHTML pre elements remain:

<p:subtree select="t:tide-data/h:html">
<p:view select="/h:html/h:body/h:pre"/>
</p:subtree>

Now only the XHTML pre elements remain.