Many editors etc proliferate your document with unrequired attributes and namespaces

<mydoc>
<ele xmlns:xyz="..." xyz:theirattr="abc">abc</ele>
</mydoc>

<xsl:stylesheet 
xmlns:xsl = "http://www.w3.org/1999/XSL/Transform" xmlns:xyz="..." >

... Standard copy ...
<xsl:template match="@xyz:*" />
</xsl:stylesheet? 

• Performing XSLT transformation will remove xyz namespace attributes and embedded namespace declarations leaving xyz namespace declaration at top on element mydoc
• Run it again and as it is now not needed, the namespace declaration on mydoc will be removed will also be removed