In a Note in 3.5.4, we advise:

If existing XSLT code has been written to use template rules in the unnamed mode, a convenient way to incorporate this code into a library package is to add a stub module that defines a new named public or final mode, in which there is a single template rule whose content is the single instruction <xsl:apply-templates/>.

The recommended instruction should be <xsl:apply-templates select="."/>