code: protected void open() {
  
          m_oldValue = m_selectionInput.m_textbox.getValue();
          CmsEmbeddedDialogHandler handler = new CmsEmbeddedDialogHandler();
          handler.setPrincipleSelectHandler(new I_CmsPrincipalSelectHandler() {
  
              public void selectPrincipal(String principal) {
  
                  if (!getFormValue().equals(principal)) {
                      setFormValueAsString(principal);
                      fireValueChange(principal);
                  }
              }
          });
          handler.openDialog(DIALOG_ID, null, null, m_configuration);
      }
docs: Opens the popup of this widget.<p>