How to preserve XML namespace in XSLT output?

Question

XSL stylesheet should output following code to Internet Explorer:

Bu

Answer 1

You can't use the preserved xml prefix. Use something like this:

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:dummy="dummy">
<xsl:namespace-alias stylesheet-prefix="dummy" result-prefix="xml"/>
<xsl:template match="/">
    <dummy:namespace prefix="vml"
                   ns="urn:schemas-microsoft-com:vml"/>
</xsl:template>
</xsl:stylesheet>

With any input, you get this result:

<xml:namespace prefix="vml" ns="urn:schemas-microsoft-com:vml" />

Answer 2

If you literally want the result as shown in the question, this is very simple to achieve:

<xsl:stylesheet version="1.0"
 xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
 <xsl:output omit-xml-declaration="yes"/>

 <xsl:template match="/">
  <xml:namespace prefix="vml" ns="urn:schemas-microsoft-com:vml"/>
 </xsl:template>
</xsl:stylesheet>

This transformation, when applied on any XML document (not used), produces the wanted result:

<xml:namespace prefix="vml" ns="urn:schemas-microsoft-com:vml"/>

However, it seems to me that you want to add a namespace node to every element of a given XML document (if this isn't so, just let me know via a commentand I'll delete this answer).

If so, here is a simple and efficient way:

<xsl:stylesheet version="1.0"
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    xmlns:vml="urn:schemas-microsoft-com:vml"
     exclude-result-prefixes="vml">
    <xsl:output omit-xml-declaration="yes" indent="yes"/>
    <xsl:strip-space elements="*"/>

    <xsl:variable name="vNamespace" select=
     "document('')/*/namespace::*[name()='vml']"/>

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

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

when applied to any document, for example this one:

<t>
    <a x="3">
        <b y="4"/>
    </a>
</t>

the wanted result is produced:

<t xmlns:vml="urn:schemas-microsoft-com:vml">
   <a x="3">
      <b y="4"/>
   </a>
</t>

This may be confusing at first sight as only the top element of the result visibly has the desired namespace node. However, by definition (look at the XML Namespace spec) if an element at the root of a (sub) tree has a given namespace node, then all of its descendent elements also have this namespace node. Even if you copy the namespace to every element, the XSLT serializer will strip it off from the serialized (text) representation of all but the top element.

In XSLT 2.0 you may simply use the <xsl:namespace> instruction:

<xsl:namespace name="vml" select="urn:schemas-microsoft-com:vml"/>