此代码应显示错误，因为标签多于dtd。但是它没有显示任何错误。怎么了？
<!DOCTYPE emaildetails [
<!ELEMENT email ( to, from, subject, body )>
<!ELEMENT to ( #PCDATA )>
<!ELEMENT from ( #PCDATA )>
<!ELEMENT subject ( #PCDATA )>
<!ELEMENT body ( #PCDATA )>
]>
<emaildetails>
<email>
<to>abc@gmail.com</to>
<from>xyz@gmail.com</from>
<subject>Hello</subject>
<help>me</help>
<body>How are you?</body>
</email>
<email>
<to>mno@gmail.com</to>
<from>xyz@gmail.com</from>
<subject>Good</subject>
<body>I am fine</body>
<help>Me</help>
</email>
</emaildetails>