XSL Second-pass template failing when attribute is selected - xslt

Question

I'm wondering if anybody can shed any light on why a particular XSL template is failing to do what is intended. I am generating XSL-FO using XSL 2.0 (Saxon HE). I want to invert certain font styles (so that italic text within an italic paragraph becomes roman, for instance). (In my actual XSL, I do this as the second part of a two-pass process. The issue occurs regardless, so my example shows a single pass for the purposes of simplicity.)
Sample input:
<?xml version="1.0" encoding="utf-8"?>
<fo:root xmlns:fo="http://www.w3.org/1999/XSL/Format">
<fo:layout-master-set>
<fo:simple-page-master master-name="skeleton">
<fo:region-body margin="1in"/>
</fo:simple-page-master>
</fo:layout-master-set>
<fo:page-sequence master-reference="skeleton">
<fo:flow flow-name="xsl-region-body">
<fo:block><fo:inline font-style="italic">A Title <fo:inline color="black" font-style="italic">With Some Roman Text</fo:inline> in the Middle</fo:inline></fo:block>
</fo:flow>
</fo:page-sequence>
</fo:root>
Sample XSL:
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet xmlns:fo="http://www.w3.org/1999/XSL/Format"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
version="2.0">
<xsl:output method="xml" indent="yes"/>
<xsl:template match="#*|node()">
<xsl:copy>
<xsl:apply-templates select="#*|node()"/>
</xsl:copy>
</xsl:template>
<xsl:template match="//fo:inline[parent::*[#font-style=current()/#font-style]]/#font-style">
<xsl:message>Found nested font-style.</xsl:message>
<xsl:attribute name="font-style">normal</xsl:attribute>
</xsl:template>
</xsl:stylesheet>
My desired result is:
<fo:root xmlns:fo="http://www.w3.org/1999/XSL/Format">
<fo:layout-master-set>
<fo:simple-page-master master-name="skeleton">
<fo:region-body margin="1in" />
</fo:simple-page-master>
</fo:layout-master-set>
<fo:page-sequence master-reference="skeleton">
<fo:flow flow-name="xsl-region-body">
<fo:block>
<fo:inline font-style="italic">
A Title
<fo:inline color="black" font-style="normal">
With Some Roman Text
</fo:inline>
in the Middle
</fo:inline>
</fo:block>
</fo:flow>
</fo:page-sequence>
</fo:root>
This is the result I get using this online tester: http://chris.photobooks.com/xml/default.htm
When I run this transform using Saxon the interior fo:inline remains italic and my debug message never appears.
I've found a workaround using for-each (if I do not attempt to select the attribute, but rather select the matching fo:inline, the template is triggered). But I'm curious to know what is wrong with this, in my opinion, much cleaner solution.
Thanks!
(Just to add a little more information, here's the less-ideal template that does get me the result I want, at least so far:
<xsl:template match="//fo:inline[parent::*[#font-style=(current()/#font-style)]]">
<xsl:message>Found nested font-style.</xsl:message>
<xsl:copy>
<xsl:for-each select="#*">
<xsl:message><xsl:value-of select="local-name()"/></xsl:message>
<xsl:choose>
<xsl:when test="local-name()='font-style'">
<xsl:attribute name="font-style">normal</xsl:attribute>
</xsl:when>
<xsl:otherwise>
<xsl:copy-of select="."/>
</xsl:otherwise>
</xsl:choose>
</xsl:for-each>
<xsl:apply-templates select="node()"/>
</xsl:copy>

Answer 1

It is possibly something to do with this line...
<xsl:template match="//fo:inline[parent::*[#font-style=current()/#font-style]]/#font-style">
In XSLT 1.0, I get an error...
The current() function may not be used in a match pattern.
I am not sure if the same happens in XSLT 2.0, but try changing the line to this, and see if that makes a difference
<xsl:template match="//fo:inline[#font-style = parent::*/#font-style]/#font-style">

Answer 2

I managed to obtain the result you are looking for changing the XPath expression to
//fo:inline[parent::*[#font-style]]/#font-style
The previous XPath expression matched no nodes in the document, so the template was never called (and so the message was also not printed).

Answer 3

Taking this to its logical extension, you probably want to convert to "normal" any fo:inline that has an odd number of ancestor fo:inline elements with the same font-style as this one (e.g. if you had italic within italic within italic then only the middle one of the three would want to be converted back to normal).
<xsl:template match="fo:inline[
count(ancestor::fo:inline[#font-style = current()/#font-style]) mod 2 = 1]">
This works because XSLT 2.0 defines current() in a pattern as the node that the pattern is being tested against (in this case the fo:inline that is the subject of the outer predicate).