dtd文件没有约束效果

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

<!DOCTYPE course-name SYSTEM "hr.dtd">

<course-name name="课程名">

<course name="大学英语" id="1">

<class-hour name="课时">36</class-hour>

<exam-form name="考核方式">考试</exam-form>

</course>

<course name="高等数学" id="2">

<class-hour name="课时">70</class-hour>

<exam-form name="考核方式">考试</exam-form>

</course>

<course name="计算机应用基础大" id="3">

<class-hour name="课时">108</class-hour>

<exam-form name="考核方式">上机考试</exam-form>

</course>

</course-name>

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

<!ELEMENT course-name(course)>

<!ELEMENT course-name(id)>

xml没有报错。