关于struts-config.xml中的<plug-in/>

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE struts-config PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 1.2//EN" "http://struts.apache.org/dtds/struts-config_1_2.dtd"><struts-config>
  <data-sources />
  <form-beans >
    <form-bean name="userForm" type="com.higpos.struts.form.UserForm" />  </form-beans>  <global-exceptions />
  <global-forwards />
  <action-mappings >
    <action
      attribute="userForm"
      input="/jsp/errors.jsp"
      name="userForm"
      parameter="method"
      path="/user"
      scope="request"
      >
      <set-property property="cancellable" value="true" />
      <forward name="suc" path="/index.jsp"></forward>
      <forward name="fai" path="/jsp/register.jsp"></forward>
    </action>  </action-mappings>
  <!-- DelegatingRequestProcessor请求处理器  可以到spring容器中取出与INPUT中名字相同的action来处理请求-->
  <controller processorClass="org.springframework.web.struts.DelegatingRequestProcessor"></controller>
  <message-resources parameter="com.higpos.struts.ApplicationResources" />
  <plug-in className="org.springframework.web.struts.ContextLoaderPlugIn">
    <set-property property="contextConfigLocation" value="/WEB-INF/classes/applicationContext.xml" />
  </plug-in>
</struts-config>
其中的<plug-in className="org.springframework.web.struts.ContextLoaderPlugIn">
    <set-property property="contextConfigLocation" value="/WEB-INF/classes/applicationContext.xml" />
  </plug-in>
不配也可以吗？
配了和不配有什么区别？