属性定义attribute

语法格式：

<!ATTLIST 元素名 属性名1 属性值类型 设置说明 属性名1 属性值类型 设置说明 属性名1 属性值类型 设置说明 属性名1 属性值类型 设置说明 >

属性声明举例：

<!ATTLIST 商品 类别 CDATA #required <!--必须的--> 颜色 CDATA #IMPLIED <!--可选的--> >

#FIXED 固定值

#FIXED "页面作者" (不用写)

默认属性（不写的话使用默认值）

属性值类型：

CDATA/ENUMERATED/ID/ENTITY

DTD案例：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE CATALOG [ <!ENTITY AUTHOR "John Doe"> <!ENTITY COMPANY "JD Power Tools,Inc."> <!ENTITY EMAIL "jd@jd-tools.com"> <!ELEMENT CATALOG (PRODUCT+)> <!ELEMENT PRODUCT (SPECIFICATIONS+,OPTIONS?,PRICE+,NOTES?)> <!ATTLIST PRODUCT NAME CDATA #IMPLIED CATEGORY (HandTool|Table|Shop-Professional) "HandTool" PARTNUM CDATA #IMPLIED PLANT (Pittsburgh|Milwaukee|Chicago) "Chicago" INVENTORY (InStock|Backordered|Discontinued) "InStock"> <!ELEMENT SPECIFICATIONS (#PCDATA)> <!ATTLIST SPECIFICATIONS WEIGHT CDATA #IMPLIED POWER CDATA #IMPLIED> <!ELEMENT OPTIONS (#PCDATA)> <!ATTLIST OPTIONS FINISH (Metal|Polished|Matte) "Matte" ADAPTER (Included|Optional|NotApplicable) "Included" CASE (HardShell|Soft|NotApplicable) "HardShell"> <!ELEMENT PRICE (#PCDATA)> <!ATTLIST PRICE MSRP CDATA #IMPLIED WHOLESALE CDATA #IMPLIED STREET CDATA #IMPLIED SHIPPING CDATA #IMPLIED> <!ELEMENT NOTES (#PCDATA)> ]>
<CATALOG>
    <PRODUCT>
        <SPECIFICATIONS >aa</SPECIFICATIONS>
        <OPTIONS>hh</OPTIONS>
        <PRICE>34</PRICE>
        <NOTES>hh</NOTES>
    </PRODUCT>
</CATALOG>