XSL formatting

I used XSLT quite extensively to generate HTML and I'm getting my HTML tags highlight in red which is irksome.

Is my XSL wrong or can I bend PHPstorm to stop highlighting my tags in red?

e.g.

<!DOCTYPE xsl:stylesheet SYSTEM "config/entities.dtd">

<xsl:stylesheet xmlns:html="http://www.w3.org/1999/xhtml"
 xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
 xmlns="http://www.w3.org/1999/xhtml"
 exclude-result-prefixes="html"
 version="1.0">

 <xsl:output encoding="utf-8"
 method="xml"
 omit-xml-declaration="yes"
 indent="yes"
                doctype-public="-//W3C//DTD XHTML 1.0 Strict//EN"
                doctype-system="http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"/>

   <!--
  |~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  |  Modifications to header block
  |~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  -->
 
 <xsl:template match="html:title">
 <title><xsl:value-of select="$search"/> on &brandName;</title>
 </xsl:template>