When to use attrubutes enumerated (one value) + required versus fixed

[karmakula77]

Hello,

I am checking some dtds and I found that all of them have a list of attributes like this:

<!ATTLIST elementName attributeName (1) #REQUIRED >

As you can see the list of enumerated values includes only one value... I was wondering why use the combination of enumerated + required instead of default value of fixed, for example:

<!ATTLIST elementName attributeName CDATA #FIXED "1">

It is not complete clear for me what is the difference between these two definitions, can someone explain me the differences and implications of using each one?

 

[tsuji]

The main different between them is that the #REQUIRED attribute is required for a document to be vaiid, and the #FIXED attribute, though, is allowed to be appeared or not appeared in the instance document.