Yelp

(The Help System)

html.xhtml

If this parameter is set to true, this stylesheet will output XHTML. Otherwise, the output is assumed to be HTML. Note that for HTML output, the importing stylesheet still needs to call xsl:namespace-alias to map the XHTML namespace to #default. The html.namespace parameter will be set automatically based on this parameter. Stylesheets can use this parameter to check the output type, for example when using xsl:element.

html.xhtml

true()