href attribute of xsl:include and xsl:import

Editors,

The XSLT specification notes that no attributes of top-level elements are
interpreted as attribute value templates.  In the case of the href
attribute of xsl:include and xsl:import, there would seem to be significant
benefit in interpreting the value as an attribute value template,
especially in conjunction with support for externally-supplied top-level
parameter values.

Could you explain the reasons for prohibiting this?

	Regards,

	Paul