code: public Object getHiddenValue(final TargetMode _mode)
          throws EFapsException
      {
          this.display = Display.HIDDEN;
          this.targetMode = _mode;
          if (this.hiddenValue == null) {
              Object obj = executeEvents(EventType.UI_FIELD_VALUE, _mode);
              if (obj == null) {
                  obj = executeEvents(EventType.UI_FIELD_FORMAT, _mode);
                  if (obj == null && getUIProvider() != null) {
                      obj = getUIProvider().getValue(this);
                  }
              } else if (getUIProvider() != null) {
                  obj = getUIProvider().transformObject(this, obj);
              }
              this.hiddenValue = obj;
          }
          return IUIValue.NULL.equals(this.hiddenValue) ? null : this.hiddenValue;
      }
docs: Method to get a plain string for this FieldValue .
  
  @see #executeEvents
  @param _mode target mode
  @throws EFapsException on error
  @return plain string
  @throws EFapsException