@Override
    public void writeInt64(int fieldNumber, long value, boolean repeated) throws IOException
    {
        final String name = schema.getFieldName(fieldNumber);

        tail = sink.writeByte(END_TAG, this,
                sink.writeStrAscii(name, this,
                        sink.writeByteArray(START_SLASH_TAG, this,
                                sink.writeStrFromLong(value, this,
                                        sink.writeByte(END_TAG, this,
                                                sink.writeStrAscii(name, this,
                                                        sink.writeByte(START_TAG, this, tail)))))));
    }
Before serializing a message/object tied to a schema, this should be called.
protostuff-xml/src/main/java/io/protostuff/XmlXOutput.java