se the current document and attempt to 
    open the new document.  This document's location is passed as an argument.
    It may update the displayed UI.
    It will probably need to update cached information useful for 
    other tasks.</P>
<LI><STRONG>Close Document:</STRONG><BR>
    <EM>Purpose:</EM> The user is done with the current 
    document. The Viewer library needs to close the document.</LI>
<P><EM>Action:</EM> The routine is responsible for closing the current document.
    Typically, it will 