XSLT: Clean up duplicate namespaces and namespace declarations

I got an XML file from a web service which had a default namespace and a namespace prefix with equal paths. In addition I had to change the root node which then lost all its defined namespaces. This resulted in various namespaces being redeclared on a bunch of various child elements, while it really should just need to be declared once on the root node.

So, this is how you may do fix this:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    xmlns="http://api.example.com/schema"
    xmlns:dup="http://api.example.com/schema">

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

    <!-- Make all elements with dup prefix use default namespace so we avoid ugly mix of both -->
    <xsl:template match="dup:*">
        <xsl:element name="{local-name()}">
            <xsl:apply-templates select="@* | node()" />
        </xsl:element>
    </xsl:template>

    <!-- For the document element (top element) -->
    <xsl:template match="/*">
        <xsl:copy>
            <!-- Add namespace to prevent redeclaration on every child element using it -->
            <xsl:namespace name="xsi" select="'http://www.w3.org/2001/XMLSchema-instance'" />
            <!-- Copy attributes and child elements -->
            <xsl:apply-templates select="@*|node()" />
        </xsl:copy>
    </xsl:template>

</xsl:stylesheet>