Add a utility XSL identity transform

This is sometimes useful to normalise DOM documents.

mdx/identity.xsl

@@ -0,0 +1,30 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+
+	identity.xsl
+
+	Identity transform.
+
+	Author: Ian A. Young <ian@iay.org.uk>
+
+-->
+<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
+
+	<!--
+		Force UTF-8 encoding for the output.
+	-->
+	<xsl:output omit-xml-declaration="no" method="xml" encoding="UTF-8"/>
+
+	<!--By default, copy text blocks, comments and attributes unchanged.-->
+	<xsl:template match="text()|comment()|@*">
+		<xsl:copy/>
+	</xsl:template>
+
+	<!--By default, copy all elements from the input to the output, along with their attributes and contents.-->
+	<xsl:template match="*">
+		<xsl:copy>
+			<xsl:apply-templates select="node()|@*"/>
+		</xsl:copy>
+	</xsl:template>
+
+</xsl:stylesheet>