code: void openPrincipalSelect() {
  
          CmsPrincipalSelectDialog dialog;
  
          m_window = CmsBasicDialog.prepareWindow(DialogWidth.max);
          WidgetType defaultType = WidgetType.groupwidget;
          if (m_principalTypeSelect.getValue().equals(I_CmsPrincipal.PRINCIPAL_USER)) {
              defaultType = WidgetType.userwidget;
          }
  
          dialog = new CmsPrincipalSelectDialog(
              this,
              m_ou == null ? A_CmsUI.getCmsObject().getRequestContext().getOuFqn() : m_ou,
              m_window,
              m_widgetType,
              m_realOnly,
              defaultType,
              m_includeWebOus);
  
          dialog.setOuComboBoxEnabled(m_ouChangeEnabled);
  
          m_window.setCaption(
              CmsVaadinUtils.getMessageText(
                  org.opencms.workplace.commons.Messages.GUI_PRINCIPALSELECTION_LIST_ACTION_SELECT_NAME_0));
          m_window.setContent(dialog);
          A_CmsUI.get().addWindow(m_window);
      }
docs: Opens the principal select dialog window.<p>