XML中的外部引用DTD

的test.xml：

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE email SYstem "test.dtd">
<email>
<von>[e-mail]</von>
<zu>[e-mail]</zu>
<titel>Hello</titel>
<text>Dear John....;-).</text>
<prior type="schnell"/>
</email>

test.dtd：

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE email [
<!ELEMENT email (von,zu,titel,text,prior)>
<!ELEMENT von (#PCDATA)>
<!ELEMENT zu (#PCDATA)>
<!ELEMENT titel (#PCDATA)>
<!ELEMENT text (#PCDATA)>
<!ATTLIST prior type CDATA #required >
]>

test.dtd中的错误代码

The markup declarations contained or pointed to by the document type declaration must be well-formed. [2]

请帮忙！！

您有重复的DOCTYPE声明.如果要引用外部DTD：

的test.xml

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE email SYstem "test.dtd">
<email>
<von>[e-mail]</von>
<zu>[e-mail]</zu>
<titel>Hello</titel>
<text>Dear John....;-).</text>
<prior type="schnell"/>
</email>

test.dtd

<!ELEMENT email (von,prior)>
<!ELEMENT von (#PCDATA)>
<!ELEMENT zu (#PCDATA)>
<!ELEMENT titel (#PCDATA)>
<!ELEMENT text (#PCDATA)>
<!ELEMENT prior EMPTY>
<!ATTLIST prior type CDATA #required >

如果您希望将DTD作为XML文件(内部子集)的一部分：

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE email [
<!ELEMENT email (von,prior)>
<!ELEMENT von (#PCDATA)>
<!ELEMENT zu (#PCDATA)>
<!ELEMENT titel (#PCDATA)>
<!ELEMENT text (#PCDATA)>
<!ELEMENT prior EMPTY>
<!ATTLIST prior type CDATA #required >
]>
<email>
<von>[e-mail]</von>
<zu>[e-mail]</zu>
<titel>Hello</titel>
<text>Dear John....;-).</text>
<prior type="schnell"/>
</email>

注意：您还缺少先前元素的ELEMENT声明.