re: empty document node or undefined

Hello,

under XML Path 2.0 section 3.2.1 Steps it says ;

'If the context node is any other kind of node, or if the context node
is an empty document or element node, then the child axis is an empty
sequence'

what is the impact of this on defining an empty document node, within
XProc, when xpath 2 is in effect ?

regards, Jim Fuller