br.mark(BUFFER_SIZE);
            XMLStreamReader xsr = XMLInputFactory.newFactory().createXMLStreamReader(br);
            xsr.nextTag();
            String nsUri = xsr.getNamespaceURI();
            try (BufferedReader br2 = reset(readerSupplier, br)) {
                xsr = XMLInputFactory.newFactory().createXMLStreamReader(br2);
                return build(source, nsUri, xsr);
            }