I want to insert an attribute 'id' into all the instances of
the same element type within a document. I've been trying to
set the value using the <xsl:number> element. How can one specify
an offset so that the sequence runs (offset + 1), (offset + 2)...
instead of 1,2,3,4,5.... I've been using the count="" attribute
to specify which elements to include in the sequence.