The XSL output method determines the default MIME type, and also some aspects of syntax in serialized tags:

The XML declaration is written by default, for output method XML. This is appropriate for a complete XML document written from a single transform. If the XML output is written as a series of nested fragments, then the XML declaration must be disabled for the embedded output using an extra flag on the <xsl:output> element. For example:

<xsl:output method="xml" omitxmldeclaration="yes"/>

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