關於struts1.2

Question

請問 validator-rules.xml 的問題:我看關於required程式碼只有寫這樣     <validator name="required"
            classname="org.apache.struts.validator.FieldChecks"
               method="validateRequired"
         methodParams="java.lang.Object,
                       org.apache.commons.validator.ValidatorAction,
                       org.apache.commons.validator.Field,
                       org.apache.struts.action.ActionMessages,
                       org.apache.commons.validator.Validator,
                       javax.servlet.http.HttpServletRequest"
                  msg="errors.required"/>org.apache.struts.validator.FieldChecks 的 validateRequired
裡面也沒有寫到關於JSP頁面顯示的語法可是卻可以做到focus 及跳出提醒頁面的動作，請問他是如何做到的！
是我哪裡沒有看到嗎?我看其他的像是
      <validator name="minlength"
            classname="org.apache.struts.validator.FieldChecks"
               method="validateMinLength"
         methodParams="java.lang.Object,
                       org.apache.commons.validator.ValidatorAction,
                       org.apache.commons.validator.Field,
                       org.apache.struts.action.ActionMessages,
                       org.apache.commons.validator.Validator,
                       javax.servlet.http.HttpServletRequest"
              depends=""
                  msg="errors.minlength"
           jsFunction="org.apache.commons.validator.javascript.validateMinLength"/>其中org.apache.commons.validator.javascript.validateMinLength
有做到客戶端驗證，裡面就有寫到focus及alert但是"required"那段沒有啊?請問他是如何做到的呢?