Inheritance: ReadOnlyBaseCollection, IRtfVisualCollection
 // ----------------------------------------------------------------------
 protected override void DoEndDocument( IRtfInterpreterContext context )
 {
     FlushPendingText();
     EndParagraph( context );
     document = new RtfDocument( context, visualDocumentContent );
     visualDocumentContent = null;
     visualDocumentContent = null;
 }
 // ----------------------------------------------------------------------
 protected override void DoBeginDocument( IRtfInterpreterContext context )
 {
     document = null;
     visualDocumentContent = new RtfVisualCollection();
 }