XSLT 2.0 Xpath error "not a node item" - xslt

Question

my first post here - sure hope someone will know the answer!
I have been able to find solutions for many issues I had, but not for this one.
The questions and answers on this site on the same subject did not solve my issue...
I have an xml containing Format specifications like
<Format>
<TagNr>92</TagNr>
<Option>A</Option>
<Format>//[N]15d</Format>
</Format>
<Format>
<TagNr>92</TagNr>
<Option>B</Option>
<Format>//3!a/3!a/15d</Format>
</Format>
TagNr + option is a unique combination within this nodeset.
I defined a key to make using the set of formats easier:
<xsl:key name="xx" match="//Format/Format" use="concat(../TagNr, ../Option)"/>
I can indeed use this key and get the correct value, but only in non-special elements; I get an error "Error in XPath 2.0 expression Not a node item" when using this key within for-each or other constructs like the one below.
What I try to achieve is the following: In other nodes processed there is a string of options for which I wish to retrieve the format for each character.
For example:
<Tag>
<TagNr>92</TagNr>
<Options>AB</Options>
</Tag>
I have been trying lots of variants of the below but no luck:
<xsl:variable name="TN"><xsl:value-of select="TagNr"/></xsl:variable>
<xsl:variable name="optList">
<xsl:analyze-string select="./Options" regex="[A-Z]">
<xsl:matching-substring>
<xsl:variable name="TNO" select="concat($TN, .)"/>
<opt>
<tag><xsl:value-of select="$TNO"/></tag>
<fmt><xsl:value-of select="key('xx', $TNO)"/></fmt>
</opt>
</xsl:matching-substring>
</xsl:analyze-string>
</xsl:variable>
Splitting into individual characters using the regex goes fine and when retrieving (only) the value for opt/tag that goes fine too.
But when I add opt/fmt, I run into the mentioned error message for the Xpath expression select="key('xx', $TNO)".
I tried defining a variable based on the key function as suggested in another thread on this site, but did not succeed.
Can anyone help me?

Answer 1

The key() function (with two arguments) searches the document containing the context node. If the context item is not a node - for example, within analyze-string - then you will get this error, because it doesn't know which document to search. The answer is to use the third argument of key() to supply this information.

Answer 2

The problem is that the context changes in your analyze-string element. Maybe the following solution will help you.
For an XML file like that :
<a>
<Format>
<TagNr>92</TagNr>
<Option>A</Option>
<Format>//[N]15d</Format>
</Format>
<Format>
<TagNr>92</TagNr>
<Option>B</Option>
<Format>//3!a/3!a/15d</Format>
</Format>
<Tag>
<TagNr>92</TagNr>
<Options>AB</Options>
</Tag>
</a>
Consider the following XSLT :
<?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" exclude-result-prefixes="xs" version="2.0">
<xsl:output indent="yes"/>
<xsl:key name="xx" match="//Format/Format" use="concat(../TagNr, ../Option)"/>
<xsl:template match="/">
<result>
<xsl:apply-templates select="//Tag"/>
</result>
</xsl:template>
<xsl:template match="Tag">
<xsl:call-template name="createOPT">
<xsl:with-param name="str" as="xs:string" select="Options"/>
</xsl:call-template>
</xsl:template>
<xsl:template name="createOPT">
<xsl:param name="str"/>
<xsl:if test="string-length($str) > 0">
<xsl:variable name="firstChar" select="substring($str,1,1)"/>
<xsl:variable name="TNO" select="concat(TagNr,$firstChar)"/>
<opt>
<tag><xsl:value-of select="$TNO"/></tag>
<fmt><xsl:value-of select="key('xx', $TNO)"/></fmt>
</opt>
<xsl:call-template name="createOPT">
<xsl:with-param name="str" select="substring($str,2)"/>
</xsl:call-template>
</xsl:if>
</xsl:template>
</xsl:stylesheet>
The result is :
<?xml version="1.0" encoding="UTF-8"?>
<result>
<opt>
<tag>92A</tag>
<fmt>//[N]15d</fmt>
</opt>
<opt>
<tag>92B</tag>
<fmt>//3!a/3!a/15d</fmt>
</opt>
</result>

Answer 3

The easiest XSLT 2.0 way to process a string character by character is the following:
<xsl:for-each select="string-to-codepoints($vStr)">
<xsl:variable name="$vChar" select=
"codepoints-to-string(.)"/>
<!-- Process $vChar here: -->
</xsl:for-each/>
You can combine this with saving the original document context into a variable (say $vDoc) and using this variable as the 3rd argument of the key() function -- which is again an XSLT 2.0 - only feature.
So, you'll have something like:
key('xx', concat($TN, $vChar), $vDoc)
Summary:
Use the string-to-codepoints() and codepoints-to-string() functions for char-by-char processing.
Use the 3-rd argument of the key() function to specify context different from the current.