code: private void menuUndoActionPerformed(java.awt.event.ActionEvent evt) {//GEN-FIRST:event_menuUndoActionPerformed
      final TabTitle title = this.getFocusedTab();
      if (title != null) {
        this.menuUndo.setEnabled(title.getProvider().undo());
        this.menuRedo.setEnabled(title.getProvider().isRedo());
      }
    }
docs: GEN-LAST:event_menuGoToFileActionPerformed