When the First Argument is a Node Set

It is possible for the first argument of the document() function to be a node set. In this case, the result is as if you had called the document() function on each node in this node set. That is, the first argument of the document() function is each node in the node set in turn. The second argument, if there is one, is the same for each iteration of the document() function. This allows you to obtain the contents of multiple documents.