[xsl] doc() and document()

["tom tom" <tomxsllist@xxxxxxxxxxx>]

I wish to reference an external XML document that may or may not actually 
exist using XSLT 2. When it doesn't exist a command such as

 <xsl:value-of select="document('ttt.xml')/one"/>

doesn't cause the transformation to fail whereas a command such as

 <xsl:value-of select="doc('ttt.xml')/one"/>

does. I am using Saxon 8.

My understanding is that, since I am using XSLT 2, the doc() function 
provides a more simple solution. Can someone advise the correct way 
implement this?

Thanks

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