Use document() function to get a reference to the inpu

I know I must have done this a hundred times, but I just can't find any example on my computer at this moment. Please straighten me out.

I wish to use the document() function to create a variable holding the input document. My stylesheet contains this element:

<xsl:variable name="main-doc" select="document('/')" />

When I run the transform, Saxon complains that I may not have any content in the prologue. I know this is a huge clue as to what I've done wrong, but I just can't see it. What have I done wrong and how do I fix it?

Thanks.

-- 
Charles Knell
cknell@xxxxxxxxxx - email