code: public boolean setHiddenInputValue(String idOrName, String value) {
          T element = findElement(By.id(idOrName));
          if (element == null) {
              element = findElement(By.name(idOrName));
              if (element != null) {
                  executeJavascript("document.getElementsByName('%s')[0].value='%s'", idOrName, value);
              }
          } else {
              executeJavascript("document.getElementById('%s').value='%s'", idOrName, value);
          }
          return element != null;
      }
docs: Sets value of hidden input field.
  @param idOrName id or name of input field to set.
  @param value value to set.
  @return whether input field was found.