Attribute Value Type  
 
Text from specification

The attribute must have been declared; the value must be of the type declared for it.

 
Explanation

All attributes used on elements in valid XML documents must have been declared in the DTD, including the xml:space and xml:lang attributes. If you declare an attribute for an element, make sure that every instance of that attribute has a value conforming to the type specified. (For attribute types, see the Attribute List Declaration entry earlier in this chapter.)