sort zones with xslt

final.xsl

<?xml version="1.0" encoding="UTF-8"?>
<!-- Stylesheet imporved by hriebl! -->
<xsl:stylesheet
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    xmlns:tei="http://www.tei-c.org/ns/1.0"
    xmlns:xs="http://www.w3.org/2001/XMLSchema"
    version="2.0"
    exclude-result-prefixes="xs tei"
    xpath-default-namespace="http://www.tei-c.org/ns/1.0">
    <xsl:output method="xml" indent="yes" />
    <xsl:strip-space elements="*"/>

    <xsl:template match="@*|node()">
        <xsl:copy>
            <xsl:apply-templates select="@*|node()"/>
        </xsl:copy>
    </xsl:template>

    <xsl:template match="zone">
        <xsl:variable name="id" select="@xml:id"/>
        <xsl:if test="not(//zone[@next = concat('#', $id)])">
            <xsl:copy>
                <xsl:apply-templates select="@*|node()"/>
            </xsl:copy>

            <xsl:variable name="next" select="substring-after(@next, '#')"/>
            <xsl:apply-templates select="//zone[@xml:id = $next]" mode="next"/>
        </xsl:if>
    </xsl:template>

    <xsl:template match="zone" mode="next">
        <xsl:copy>
            <xsl:apply-templates select="@*|node()"/>
        </xsl:copy>

        <xsl:variable name="next" select="substring-after(@next, '#')"/>
        <xsl:apply-templates select="//zone[@xml:id = $next]" mode="next"/>
    </xsl:template>

</xsl:stylesheet>

source.xml

<?xml version="1.0" encoding="UTF-8"?>
<TEI xmlns="http://www.tei-c.org/ns/1.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.tei-c.org/ns/1.0">
    
    <sourceDoc>
        <surface n="1r">
            <zone xml:id="a"/>
            <zone xml:id="b" next="#d"/>
            <zone xml:id="c"/>
            <zone xml:id="d" next="#g"/>
            <zone xml:id="e"/>
        </surface>
        <surface n="1v">
            <zone xml:id="f"/>
            <zone xml:id="g" next="#c"/>
        </surface>
    </sourceDoc>
</TEI>

target.xml

<?xml version="1.0" encoding="UTF-8"?>
<TEI xmlns="http://www.tei-c.org/ns/1.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.tei-c.org/ns/1.0">
    
    <sourceDoc>
        <surface n="1r">
            <zone xml:id="a"/>
            <zone xml:id="b" next="#d"/>
            <zone xml:id="d" next="#g"/>
            <zone xml:id="g" next="#c"/>
            <zone xml:id="c"/>
            <zone xml:id="e"/>
        </surface>
        <surface n="1v">
            <zone xml:id="f"/>
        </surface>
    </sourceDoc>
</TEI>

xslt.xsl

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet 
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform" 
    xmlns:tei="http://www.tei-c.org/ns/1.0" 
    xmlns:xs="http://www.w3.org/2001/XMLSchema" 
    version="2.0" 
    exclude-result-prefixes="xs tei" 
    xpath-default-namespace="http://www.tei-c.org/ns/1.0">
    <xsl:output method="xml" indent="yes" />
    <xsl:strip-space elements="*"/>
    
    <xsl:variable name="zonesort">
        <xsl:call-template name="zonesort"/>
    </xsl:variable>
    <xsl:template name="zonesort">
        <xsl:apply-templates select="/" mode="zonesort"/>
    </xsl:template>
    
    <xsl:template match="/">
        <xsl:apply-templates select="$zonesort" mode="cleanup"/>
    </xsl:template>
    
    <!-- generic copy in all modes -->
    <xsl:template match="@*|node()" mode="#all">
        <xsl:copy>
            <xsl:apply-templates select="@*|node()" mode="#current"/>
        </xsl:copy>
    </xsl:template>
    

    
   <xsl:template match="zone[@next][@xml:id != preceding::zone/substring-after(@next, '#')]" mode="zonesort">
       <xsl:copy-of select="current()"/>
       <!-- grab the next zone ¯\_(ツ)_/¯ -->
       <xsl:variable name="nxt" select="substring-after(@next, '#')"/>
       <xsl:call-template name="zonecopy">
           <xsl:with-param name="nxt" select="$nxt"/>
       </xsl:call-template>
       
<!--       <!-\- grab next zones next zone ¯\_(ツ)_/¯ -\->
       <xsl:variable name="nxt" select="//zone[@xml:id = $nxt][@next]/substring-after(@next, '#')"/>
       <xsl:apply-templates select="//zone[@xml:id = $nxt]"/>
       
       <!-\- grab next zones next zones next zone  ¯\_(ツ)_/¯  -\->
       <xsl:variable name="nxt" select="//zone[@xml:id = $nxt][@next]/substring-after(@next, '#')"/>
       <xsl:apply-templates select="//zone[@xml:id = $nxt]"/>
    
       <!-\- grab next zones next zones next zone  ¯\_(ツ)_/¯  -\->
       <xsl:variable name="nxt" select="//zone[@xml:id = $nxt][@next]/substring-after(@next, '#')"/>
       <xsl:apply-templates select="//zone[@xml:id = $nxt]"/>
       
       <!-\- grab next zones next zones next zone  ¯\_(ツ)_/¯  -\->
       <xsl:variable name="nxt" select="//zone[@xml:id = $nxt][@next]/substring-after(@next, '#')"/>
       <xsl:apply-templates select="//zone[@xml:id = $nxt]"/>
       
       <!-\- grab next zones next zones next zone  ¯\_(ツ)_/¯  -\->
       <xsl:variable name="nxt" select="//zone[@xml:id = $nxt][@next]/substring-after(@next, '#')"/>
       <xsl:apply-templates select="//zone[@xml:id = $nxt]"/>
       
       <!-\- grab next zones next zones next zone  ¯\_(ツ)_/¯  -\->
       <xsl:variable name="nxt" select="//zone[@xml:id = $nxt][@next]/substring-after(@next, '#')"/>
       <xsl:apply-templates select="//zone[@xml:id = $nxt]"/>
       
       <!-\- grab next zones next zones next zone  ¯\_(ツ)_/¯  -\->
       <xsl:variable name="nxt" select="//zone[@xml:id = $nxt][@next]/substring-after(@next, '#')"/>
       <xsl:apply-templates select="//zone[@xml:id = $nxt]"/>-->
   </xsl:template>
    
    <xsl:template name="zonecopy">
        <xsl:param name="nxt"/>
        <xsl:copy-of select="//zone[@xml:id = $nxt]"/>
        <xsl:if test="//zone[@xml:id = $nxt]/@next">
            <xsl:call-template name="zonecopy">
                <xsl:with-param name="nxt" select="//zone[@xml:id = $nxt]/substring-after(@next, '#')"/>
            </xsl:call-template>
        </xsl:if>
    </xsl:template>
    
    
    <xsl:template match="zone[@xml:id = preceding::zone/@xml:id]" mode="cleanup"/>
    
    <xsl:template match="sourceDoc/surface" mode="whatsnext0">
        <xsl:element name="pb" namespace="http://www.tei-c.org/ns/1.0">
            <xsl:attribute name="n" select="@n"/>
        </xsl:element>
        <xsl:apply-templates/>
    </xsl:template>

</xsl:stylesheet>

trying to sort the zones according to the next attribute