[xsl] document nodes.

["Andre Cusson akhu01@xxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>]

Hi,

There is some Saxon/Oxygen behavior that I do not seem to grasp.
I made a simplified use case to present it.

I have an xml document (thingtest.xml) that looks somewhat like this:

<?xml version="1.0" encoding="UTF-8"?>
<thing id="main" title="something">
    <thing id="group1">...</thing>
    <thing id="group2">...</thing>
    <thing id="group3">...</thing>
</thing>

and I have a stylesheet (thingtest.xslt) that reads this file and tries to
"message" the value of the title attribute on the main (root) element, like:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform";
    xmlns:xs="http://www.w3.org/2001/XMLSchema";
    xmlns:math="http://www.w3.org/2005/xpath-functions/math";
    exclude-result-prefixes="xs math"
    version="3.0">

    <xsl:template match="/">
        <xsl:variable name="struct" select="doc('thingtest.xml')/*"/>
        <xsl:message select="$struct/@title"/>
    </xsl:template>
</xsl:stylesheet>

Now running this produces this error
[Saxon-PE] Error XTDE0420 while evaluating xsl:message at line 10 of
file:servercfg/thingtest.xslt: Cannot create an attribute node (title)
whose parent is a document node.
Mind you, $struct should not be a document mode as it is the child of a
document node.
Where it gets a little exotic for me is when I replace the message
instruction by either :
 <xsl:message select="'' || $struct/@title"/>
or
 <xsl:message select="string-join(($struct/@title))"/>
Then, it works fine.

I do not mind adding a null string if I have to, but better
understanding why may better contribute to my happiness.
What am I doing wrong this time ... ;)
Thank you,
Regards.