XSL associative sorting using a field substring - xslt

Question

The transformation I am writing must compose a comma separated string value from a given node set. The resulting string must be sorted according to a random (non-alphabetic) mapping for the first character in the input values.
I came up with this:
<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet
version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:tmp="http://tempuri.org"
exclude-result-prefixes="tmp"
>
<xsl:output method="xml" indent="yes"/>
<tmp:sorting-criterion>
<code value="A">5</code>
<code value="B">1</code>
<code value="C">3</code>
</tmp:sorting-criterion>
<xsl:template match="/InputValueParentNode">
<xsl:element name="OutputValues">
<xsl:for-each select="InputValue">
<xsl:sort select="document('')/*/tmp:sorting-criterion/code[#value=substring(.,1,1)]" data-type="number"/>
<xsl:value-of select="normalize-space(.)"/>
<xsl:if test="position() != last()">
<xsl:text>,</xsl:text>
</xsl:if>
</xsl:for-each>
</xsl:element>
</xsl:template>
</xsl:stylesheet>
It doesn't work and looks like the XPath document('')/*/tmp:sorting-criterion/code[#value=substring(.,1,1)] does not evaluate as I expect. I've checked to substitute the substring(.,1,1) for a literal and it evaluates to the proper value.
So, am I missing something that makes the sorting XPath expression not to evaluate as I expect or is it simply impossile to do it this way?
If not possible to create a XPath expression that works, is there a work around to achieve my purpose?
Note: I'm constrained to XSLT-1.0
Sample Input:
<?xml version="1.0" encoding="utf-8"?>
<InputValueParentNode>
<InputValue>A input value</InputValue>
<InputValue>B input value</InputValue>
<InputValue>C input value</InputValue>
</InputValueParentNode>
Expected ouput:
<?xml version="1.0" encoding="utf-8"?>
<OutputValues>B input value,C input value,A input value</OutputValues>

Answer 1

Replace the self::node() abbreviation ., with current() function.
A better predicate would be: starts-with(normalize-space(current()),#value)

Answer 2

Besides changing transformation according to Alejandro´s answer, I found it better to use a XSL variable for th mapping data to avoid declaration of a dummy namespace (tmp) as seen in Dimitre´s answer to another related question.
My final implementation:
<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet
version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
>
<xsl:output method="xml" indent="yes"/>
<xsl:template match="/InputValueParentNode">
<xsl:variable name="sorting-map">
<i code="A" priority="5"/>
<i code="B" priority="1"/>
<i code="C" priority="3"/>
</xsl:variable>
<xsl:variable name="sorting-criterion" select="document('')//xsl:variable[#name='sorting-map']/*"/>
<xsl:element name="OutputValues">
<xsl:for-each select="InputValue">
<xsl:sort select="$sorting-criterion[#code=substring(normalize-space(current()),1,1)]/#priority" data-type="number"/>
<xsl:value-of select="normalize-space(current())"/>
<xsl:if test="position() != last()">
<xsl:text>,</xsl:text>
</xsl:if>
</xsl:for-each>
</xsl:element>
</xsl:template>
</xsl:stylesheet>