@Override
    public boolean isDeclared(String qName) {
        int index = getIndex(qName);
        if (index < 0) {
            throw new IllegalArgumentException();
        }
        String type = parser.getAttributeType(elementName, qName);
        return (type != null);
    }
@return false unless the attribute was declared in the DTD.
@throws java.lang.IllegalArgumentException
            When the supplied names do not identify an attribute.
src/nu/validator/gnu/xml/aelfred2/SAXDriver.java