XSLT parser/content error xml to text for doctype cesAlign

<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet xmlns:xsl="http://ift.tt/tCZ8VR"
            version="1.0">

  <xsl:output method="text" encoding="utf-8" />

  <xsl:template match="linkGrp">
    <xsl:value-of select="normalize-space()"/>
    <xsl:text>&#xa;</xsl:text> <!-- newline after sentences -->
  </xsl:template>

</xsl:stylesheet>

When I attempt to run the above xslt stylesheet on the following cesAlign xml doc

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE cesAlign PUBLIC "-//CES//DTD XML cesAlign//EN" "">
<cesAlign version="1.0">
<linkGrp targType="s" fromDoc="en/1976/7277/69682_1of1.xml.gz" toDoc="zh/1976/7277/4041906_1of1.xml.gz">
<link id="SL0" xtargets=";1" />
<link id="SL1" xtargets="1;2" />
<link id="SL2" xtargets="2;3" />
...

I encounter this error:

parser error : Content error in the external subset
<!DOCTYPE cesAlign PUBLIC "-//CES//DTD XML cesAlign//EN" "">

Is there some place where I should be specifying this particular input doc type (cesAlign)?