How to call the validation service in webdynpro?

Hi all,

I found in webdynpro' view controller, there is a hook method named wdDoBeforeAction:

  //@@begin javadoc:wdDoBeforeAction
  /**
   * Hook method called for additional validation of user input. <p>
   *
   * @param validation Interface for reporting validation errors
   */
  //@@end
  public void wdDoBeforeAction(com.sap.tc.webdynpro.progmodel.api.IWDBeforeAction validation)
  {
    //@@begin wdDoBeforeAction
    //@@end
  }

how to use this hook method? Could anyone give me some information about this hook method?

Thanks and Best regards

Deyang