[xsl] Use of xsl:document

["tom tom" <tomxsllist@xxxxxxxxxxx>]

I wish to store an external XML file as the value of an XSLT variable using 
XSLT 2.0. This is how it is presently being acheived:

<xsl:variable name="Xml" as="document-node()" 
select="document('test.xml')"/>

Should I be using the xsl:document function instead?
If I should, why?
Is there any use for the xsl:document function other than the fact it allows 
validation?

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