Re: document nodes.

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\xA0an xml document (thingtest.xml) that looks somewhat like this:

<?xml version="1.0" encoding="UTF-8"?>
<thing id="main" title="something">
 \xA0 \xA0 <thing id="group1">...</thing>
 \xA0 \xA0 <thing id="group2">...</thing>
 \xA0 \xA0 <thing id="group3">...</thing>
</thing>

and I have a stylesheet\xA0(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 <http://www.w3.org/1999/XSL/Transform>"
 \xA0 \xA0 xmlns:xs="http://www.w3.org/2001/XMLSchema <http://www.w3.org/2001/XMLSchema>"
 \xA0 \xA0 xmlns:math="http://www.w3.org/2005/xpath-functions/math <http://www.w3.org/2005/xpath-functions/math>"
 \xA0 \xA0 exclude-result-prefixes="xs math"
 \xA0 \xA0 version="3.0">

 \xA0 \xA0 <xsl:template match="/">
 \xA0 \xA0 \xA0 \xA0 <xsl:variable name="struct" select="doc('thingtest.xml')/*"/>
 \xA0 \xA0 \xA0 \xA0 <xsl:message select="$struct/@title"/>
 \xA0 \xA0 </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 :
 \xA0<xsl:message select="'' || $struct/@title"/>
or
 \xA0<xsl:message select="string-join(($struct/@title))"/>
Then, it works fine.

I do not mind adding a null string if I have to, but better understanding\xA0why may better contribute to my happiness.
What am I doing wrong this time ... ;)
Thank you,
Regards.