One of the graduate students with whom I work is typing a document in which
he often references particular line numbers. Sometimes when he alters the
document, it changes the line numbering and his has to go from page to page
changing all of the line numbers being referenced.  Is there a field code or
some other citing or referencing code that he could use that would
automatically update the line number information so that he wouldn't need to
manually change it each time he adds or removes lines in his document?