public String getAttributeDefaultValue(String name, String aname) {
        AttributeDecl attribute = getAttribute(name, aname);
        return (attribute == null) ? null : attribute.value;
    }
Retrieve the default value of a declared attribute.

@param name
           The name of the associated element.
@param aname
           The name of the attribute.
@return The default value, or null if the attribute was #IMPLIED or
        simply undeclared and unspecified.
@see #getAttributeExpandedValue
src/nu/validator/gnu/xml/aelfred2/XmlParser.java