@Override
    public void setDTDHandler(DTDHandler handler) {
        if (handler == null) {
            handler = base;
        }
        this.dtdHandler = handler;
    }
<b>SAX1, SAX2</b>: Set the DTD handler for this parser.

@param handler
           The object to receive DTD events.
src/nu/validator/gnu/xml/aelfred2/SAXDriver.java