为什么这个DTD无效？

Question

我试着用1-2验证验证这个DTD，但是我在为什么它是无效的不确定：

DTD代码：

任何帮助将不胜感激！

<?xml version="1.0" encoding="UTF-8"?> 
<!DOCTYPE cars 
[ 
    <!ELEMENT car (maker, model, year, colour, engine, number_of_doors, accessories)> 

    <!ELEMENT maker (#PCDATA)> 
    <!ELEMENT model (#PCDATA)> 
    <!ELEMENT year (#PCDATA)> 
    <!ELEMENT colour (#PCDATA)> 
    <!ELEMENT engine (number_of_cylinders)> 
    <!ELEMENT number_of_doors (#PCDATA)> 
    <!ELEMENT accessories (#PCDATA)> 

    <!ELEMENT number_of_cylinders (#PCDATA)> 

    <!ATTLIST accessories radio (yes|no) #REQUIRED 
     air_conditioning (yes|no) #REQUIRED 
     power_windows (yes|no) #REQUIRED 
     power_steering (yes|no) #REQUIRED 
     power_brakes (yes|no) #REQUIRED 
    > 
]> 

Answer 1

，从而与内部DTD子集XML文档是有效的，做如下修改：

1. 更改文档元素从cars到car。

2. 构建与给定内部子集关联的XML。

   <?xml version="1.0" encoding="UTF-8"?> 
   <!DOCTYPE car 
   [ 
   <!ELEMENT car (maker, model, year, colour, engine, number_of_doors, accessories)> 
   
   <!ELEMENT maker (#PCDATA)> 
   <!ELEMENT model (#PCDATA)> 
   <!ELEMENT year (#PCDATA)> 
   <!ELEMENT colour (#PCDATA)> 
   <!ELEMENT engine (number_of_cylinders)> 
   <!ELEMENT number_of_doors (#PCDATA)> 
   <!ELEMENT accessories (#PCDATA)> 
   
   <!ELEMENT number_of_cylinders (#PCDATA)> 
   
   <!ATTLIST accessories radio (yes|no) #REQUIRED 
       air_conditioning (yes|no) #REQUIRED 
       power_windows (yes|no) #REQUIRED 
       power_steering (yes|no) #REQUIRED 
       power_brakes (yes|no) #REQUIRED> 
   ]> 
   <car> 
       <!-- Finish building out the XML per the internal subset. --> 
   </car> 
   

Answer 2

你可以用这个验证是最适合DTD https://validator.w3.org/check