> You can define a default value of parameter in a way to report omission:
>
> <xsl:param name="somevar">
>  <xsl:sequence select="'default'"/>
>  <xsl:message select="somevar is not specified"/>
> </xsl:param>
> --
> VN
>

The spec offers no guarantee that the default value will be evaluated only if
it is needed.

Michael Kay
Saxonica