code: public void updateNewRelsExt(String pid) throws Exception {
          if (!hasRelsExt() && getTabIndex("New RELS-EXT...") == -1) {
              m_tabbedPane.insertTab("New RELS-EXT...",
                                     newIcon,
                                     new NewRelsExtDatastreamPane(m_owner,
                                                                  pid,
                                                                  this),
                                     "Add a RELS-EXT datastream to this object",
                                     getTabIndex("New..."));
              int i = getTabIndex("New RELS-EXT...");
              m_tabbedPane.setBackgroundAt(i, Administrator.DEFAULT_COLOR);
          } else if (hasRelsExt() && getTabIndex("New RELS-EXT...") != -1) {
              m_tabbedPane.remove(getTabIndex("New RELS-EXT..."));
          }
      }
docs: Set the content of the "New Rels-Ext..." JPanel to a fresh new datastream
  entry panel, and switch to it, if needed.
  
  @throws Exception