XSL won't write xmlns:xsl? - xslt

Question

How do I write the XSL namespace in my output?
I'm using XSL to analyze an XSL document and report problems it finds, including copying the node. The problem is that I can't get xmlns:xsl="http://www.w3.org/1999/XSL/Transform" written into the output's root node, which means it gets repeated every time I copy an xsl:* element.
This doesn't seem to happen with other namespaces. For example, take the following XSL
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:custom="custom uri" xmlns:custom2="custom2 uri" exclude-result-prefixes="" version="3.0">
<xsl:output method="xml" version="1.0" encoding="UTF-8" indent="yes"/>
<xsl:template match="/" name="xsl:initial-template">
<custom:element xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:element name="custom2:function">
<xsl:attribute name="name">whatever</xsl:attribute>
</xsl:element>
<xsl:element name="custom2:function">
<xsl:attribute name="name">whatever2</xsl:attribute>
</xsl:element>
</custom:element>
</xsl:template>
</xsl:stylesheet>
When run against any XML document, I get what I expect except that xmlns:xsl is missing from custom:element even though I specify it and exclude-result-prefixes is explicitly blank... but that's fine, it's not used in the output.
<custom:element xmlns:custom="custom uri" xmlns:custom2="custom2 uri">
<custom2:function name="whatever"/>
<custom2:function name="whatever2"/>
</custom:element>
However, if I replace both name="custom2:function" with name="xsl:function" like so...
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:custom="custom uri" xmlns:custom2="custom2 uri" exclude-result-prefixes="" version="3.0">
<xsl:output method="xml" version="1.0" encoding="UTF-8" indent="yes"/>
<xsl:template match="/" name="xsl:initial-template">
<custom:element xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:element name="xsl:function">
<xsl:attribute name="name">whatever</xsl:attribute>
</xsl:element>
<xsl:element name="xsl:function">
<xsl:attribute name="name">whatever2</xsl:attribute>
</xsl:element>
</custom:element>
</xsl:template>
</xsl:stylesheet>
then xmlns:xsl is still missing from custom:element and I get
<custom:element xmlns:custom="custom uri" xmlns:custom2="custom2 uri">
<xsl:function xmlns:xsl="http://www.w3.org/1999/XSL/Transform" name="whatever"/>
<xsl:function xmlns:xsl="http://www.w3.org/1999/XSL/Transform" name="whatever2"/>
</custom:element>
instead of what I want:
<custom:element xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:custom="custom uri" xmlns:custom2="custom2 uri">
<xsl:function name="whatever"/>
<xsl:function name="whatever2"/>
</custom:element>
How do I change my stylesheet to declare xmlns:xsl="http://www.w3.org/1999/XSL/Transform" I the root node?

Answer 1

With Saxon a namespace alias helps:
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:custom="custom-uri" xmlns:custom2="custom2-uri" version="3.0">
<xsl:output method="xml" version="1.0" encoding="UTF-8" indent="yes"/>
<xsl:namespace-alias stylesheet-prefix="axsl" result-prefix="xsl" xmlns:axsl="http://www.w3.org/1999/XSL/Transform-alias"/>
<xsl:template match="/" name="xsl:initial-template">
<custom:element xmlns:axsl="http://www.w3.org/1999/XSL/Transform-alias">
<xsl:element name="xsl:function">
<xsl:attribute name="name">whatever</xsl:attribute>
</xsl:element>
<xsl:element name="xsl:function">
<xsl:attribute name="name">whatever2</xsl:attribute>
</xsl:element>
</custom:element>
</xsl:template>
</xsl:stylesheet>
https://xsltfiddle.liberty-development.net/gVhEaiX outputs
<custom:element xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:custom="custom-uri"
xmlns:custom2="custom2-uri">
<xsl:function name="whatever"/>
<xsl:function name="whatever2"/>
</custom:element>
Most times you would just put the namespace declaration on the root element with e.g.
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:custom="custom-uri" xmlns:custom2="custom2-uri" version="3.0"
xmlns:axsl="http://www.w3.org/1999/XSL/Transform-alias">
<xsl:output method="xml" version="1.0" encoding="UTF-8" indent="yes"/>
<xsl:namespace-alias stylesheet-prefix="axsl" result-prefix="xsl" />
<xsl:template match="/" name="xsl:initial-template">
<custom:element>
<xsl:element name="xsl:function">
<xsl:attribute name="name">whatever</xsl:attribute>
</xsl:element>
<xsl:element name="xsl:function">
<xsl:attribute name="name">whatever2</xsl:attribute>
</xsl:element>
</custom:element>
</xsl:template>
</xsl:stylesheet>
I was not sure whether you want to restrict it to a certain element so the first sample declares it on that element and then of course additionally on the xsl:namespace-alias so that it makes sense.