code: private String generateValue() {
  
          String result = "";
          for (CmsCheckBox checkbox : m_checkboxes) {
              if (checkbox.isChecked()) {
                  result += checkbox.getInternalValue() + ",";
              }
          }
          if (result.contains(",")) {
              result = result.substring(0, result.lastIndexOf(","));
          }
          return result;
      }
docs: Generate a string with all selected checkboxes separated with ','.
  
  @return a string with all selected checkboxes