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warning /xsl:stylesheet/xsl:output[@method = 'xml'][//xsl:template[starts-with(@match, '/') and (count (.//html | .//HTML) > 0)]]

Output method xml

Using method="xml" while the root template generates html or HTML elements causes incorrect serialization. Switch to method="html" when producing HTML output.

Incorrect:

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:output method="xml"/>
  <xsl:template match="/">
    <html><body><xsl:value-of select="."/></body></html>
  </xsl:template>
</xsl:stylesheet>

Correct:

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:output method="html"/>
  <xsl:template match="/">
    <html><body><xsl:value-of select="."/></body></html>
  </xsl:template>
</xsl:stylesheet>