Hallo Caro,
<xsl:output method="html" version="4.01 Transitional" indent="no" encoding="ISO-8859-1" doctype-public="http://www.w3.org/TR/html4/loose.dtd" />
"Transitional" gehört zum Formal Public Identifier, also in doctype-public:
~~~xml
<xsl:output method="html" version="4.01" indent="no" encoding="ISO-8859-1"
doctype-public="-//W3C//DTD HTML 4.01 Transitional//EN"
doctype-system="http://www.w3.org/TR/html4/loose.dtd"/>
Grüße,
Thomas