files/en-us/web/xml/xpath/reference/functions/document/index.md
The document finds a node-set in an external document, or multiple external documents, and returns the resulting node-set.
document( URI [,node-set] )
URI
node-set (optional)
A node-set.
node-set argument's expression. If the node-set argument is omitted, the entire fragment will be returned.URI argument is a node-set, and the second argument is present, each node in the node-set will be evaluated as a separate URI, and the returned node-set will be as if the document function has been called multiple times (each time with the same second argument just as given in the function call) and the resulting node-sets had been concatenated into a single node-set.document("") would return the root node of the current document.This function is an XSLT-specific addition to XPath. It is not a part of the core XPath function library.
Supported.