The Tor Browser / file revision

 <?xml version="1.0"?>

 <?xml-stylesheet type="text/xsl" href="#stylesheet"?>

 <!DOCTYPE root [

   <!ATTLIST xsl:stylesheet id ID #IMPLIED>

 ]>

 <root>

 <xsl:stylesheet id="stylesheet" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">

   <xsl:attribute-set name="a">

 	<xsl:attribute name="b">c</xsl:attribute>

   </xsl:attribute-set>

   <xsl:template match="/">

     <b>Please output something!</b>

   </xsl:template>

   <xsl:attribute-set name="a">

 	<xsl:attribute name="b">c</xsl:attribute>

   </xsl:attribute-set>

 </xsl:stylesheet>

 <doc id="foo">this</doc>

 </root>