web.xml文件下面标红的为啥会报错

web.xml文件下面标红的为啥会报错

<!DOCTYPE web-app PUBLIC

 "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"

 "http://java.sun.com/dtd/web-app_3_1.dtd" >

<?xml version="1.0" encoding="UTF-8"?>

<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

    xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:javaee="http://java.sun.com/xml/ns/javaee"

    xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"

    xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/webapp_2_4.xsd"

    id="WebApp_ID" version="2.4">