losing the current document and opening another.  The routine should 
    check the new document for correctness 
    (as described for "Open," above).  It should update 
    the document-display UI so that it corresponds to the new document.
    If there's a problem, it should discard the document-display UI.</DD>
<DT><STRONG>Close</STRONG></DT>
<DD>This routine is responsible for closing the current document.  It 
    should close the document file and discard the document-display UI.</DD>
</DL>

<P>It's 