anchor.diff:    const setupReplTabClickHandler = ($tab) => {
       $tab.click(() => {
         if (alreadySelected($tab)) { return; }
  -      cd.unloadFile(selectedTabFilename());
  +      cd.unloadFile($selectedTab().text());
         cd.openRepl();
         select($tab);
       });
  
positive.code:   // Alt-O ==> toggleOutputFile()
  
    cd.toggleOutputFile = () => {
      switch (selectedTabFilename()) {
      default               : cd.loadFile('stdout'); break;
      case 'stdout'         : cd.loadFile('stderr'); break;
      case 'stderr'         : cd.loadFile('status'); break;
  
negative.code: 
    cd.setFilenameTab = (filename) => {
      // filename = from filename-knave, stdout, stderr, status (never +REPL)
      if ($selectedTab().text() === $replTab().text()) {
        cd.closeRepl();
      }
      const id = cd.isOutputFile(filename) ? `radio_${filename}` : 'current_filename';
  