XPath: Find Next Occurrence of an Element in an Ancestor - xpath

Question

I am trying to find the next instance of within a section of sec-type='reading'.
XML Sample:
<?xml version="1.0" encoding="US-ASCII"?>
<book>
<sec sec-type="reading">
<title>Section 1</title>
<p>Sample <bold>Bold</bold>Text <fn><label>1</label></fn> Some more text</p>
<!-- more variations of stuff at various levels -->
<sec>
<title>Section 1.1</title>
<p>Another paragraph with a footnote <fn><label>2</label></fn></p>
</sec>
<sec>
<title>Section 1.2</title>
<p>Another paragraph with a footnote <fn><label>3</label></fn></p>
</sec>
</sec>
<sec sec-type="reading">
<title>Section 2</title>
<p>Sample <bold>Bold</bold>Text <fn><label>6</label></fn> Some more text</p>
<!-- more variations of stuff at various levels -->
<sec>
<title>Section 2.1</title>
<p>Another paragraph with a footnote <fn><label>8</label></fn></p>
</sec>
<sec>
<title>Section 2.2</title>
<p>Another paragraph with a footnote <fn><label>9</label></fn></p>
</sec>
</sec>
</book>
The purpose is to see if the FN labels are sequentially ordered within a section. I've numbered the second section with 6-9 to make it easier to see if it's working.
This is what I want:
Footnote 1 [Next: 2]
Footnote 2 [Next: 3]
Footnote 3 [Next: ]
Footnote 6 [Next: 8]
Footnote 8 [Next: 9]
Footnote 9 [Next: ]
The eventual goal is to return a warning for Footnote 6 [Next: 8]
This is the schematron I've got so far. This gives me:
Footnote 1 [Next: 2]
Footnote 2 [Next: 3]
**Footnote 3 [Next: 6]**
Footnote 6 [Next: 8]
Footnote 8 [Next: 9]
Footnote 9 [Next: ]
It finds the next instance of the footnote. However, I don't want it to cross the sections - so Footnote 3 [Next: 6] is wrong.
<?xml version="1.0" encoding="UTF-8"?>
<schema xmlns="http://purl.oclc.org/dsdl/schematron"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
queryBinding="xslt2" >
<!--check if footnotes are sequential within a reading -->
<pattern id="footnote-sequential">
<rule context="fn">
<let name="next" value="following::fn[1]/label/text()"/>
<assert test="number(label/text()) > 40">
Footnote <value-of select='label'/>
[Next: <value-of select="$next"/>]
</assert>
</rule>
</pattern>
</schema>
Note: number(label/text()) > 40 in the assert is there to catch everything at the moment. It'll eventually be something along the lines of number(current)+1 != number(next)
The closest I've gotten is ancestor::sec[#sec-type='reading']//following::fn[1]/label/text() - but that looses the "next" and gives me weird results like this:
Footnote 1 [Next: 1236]
Footnote 2 [Next: 1236]
Footnote 3 [Next: 1236]
Footnote 6 [Next: 689]
Footnote 8 [Next: 689]
Footnote 9 [Next: 689]

Answer 1

You need intersect.
[EDIT]
Set $next to the fn element instead of the label text:
<let name="next" value="following::fn[1]"/>
[/EDIT]
Go to your current section and take all footnotes of this section:
<let name="sect-fns" value="ancestor::sec[#sec-type='reading']//fn" />
Make the intersect on $next and $sect-fns:
<let name="next" value="$next intersect $sect-fns" />
Check if $next is empty or its label is number(./label) + 1:
<assert test="not($next) or number(./label) + 1 = number($next/label)">