structs-报错01-Document is invalid: no grammar found

一时手贱，把structs-config.xml文件中的一段话删了，结果老是报错。
报错内容：document is invalid: no grammar found
[html] 
<?xml version="1.0" encoding="utf-8"?> 
<strong><span style="color:#ff0000;"><!doctype struts-config public 
       "-//apache software foundation//dtd tiles configuration 1.3//en" 
       "https://jakarta.apache.org/struts/dtds/struts-config_1_3.dtd"></span></strong> 
<struts-config> 
    <form-beans> 
        <form-bean name="helloform" type="com.mars.demo01.structs01.form.helloform" /> 
    </form-beans> 
    <!-- 用于配置actionform --> 
    <global-exceptions /><!-- 用于配置全局异常 --> 
    <global-forwards /><!-- 用于配置全局跳转 --> 
    <action-mappings> 
        <action attribute="helloform" input="/demo01/demo01_hello." 
            name="helloform" path="/demo01/demo01_hello" scope="request" 
            type="com.mars.demo01.structs01.action.helloaction" cancellable="true"> 
            <forward name="show" path="/demo01/demo01_hello.jsp"></forward> 
        </action> 
 
    </action-mappings> 
    <!-- 用于配置action --> 
    <message-resources parameter="com.mars.demo01.structs01.applicationresources" /> 
</struts-config> 
然后恢复原样，结果又好了，所以这句话是不能删的。在网上查了查，发现这是一个定义格式的东东。怎么弄的这么麻烦。