Attribute Value Type
The attribute must have been declared; the value must be of the type declared for it.
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.)