the UI by 
        sending a MSG_VD_CLOSE to the <STRONG>ViewerDialog</STRONG>.
    </UL>
    <P>The routine is passed a <STRONG>ViewerParams</STRONG> structure 
       which provides either state information or information about 
       the document to be opened.  The routine should return an optr (null 
       if there was a problem).  The Viewer library will pass this optr 
       as an argument to subsequent routines.</P>
    <P>If you're restoring from state, you'll be passed a block of memory 
       