XPointer does not specify the document, only the part of the document
The rest of the URL specifies the document
http://www.w3.org/TR/1998/REC-xml-19980210.xml#xptr(id("ebnf"))
http://www.w3.org/TR/1998/REC-xml-
19980210.xml#xptr(descendant::language[position()=2])
http://www.w3.org/TR/1998/REC-xml-19980210.xml#ebnf
http://www.w3.org/TR/1998/REC-xml-19980210.xml
#xptr(/child::spec/child::body/child::*/child::language[ position() = 2])
http://www.w3.org/TR/1998/REC-xml-
19980210.xml#/1/14/2
http://www.w3.org/TR/1998/REC-xml-
19980210.xml#xptr(id("ebnf"))xptr(id("EBNF"))
In fact, these URIs are just six different ways of pointing to the same element of the document at http://www.w3.org/TR/1998/REC-xml-19980210.xml.