RIB V11 extension

Hi,

Can someone please share the steps or a document which explains on extending a subscription message in RIB V11. Example if we need to add additional data elements into the  message subscribed by RMS, what all needs to be done.

At a high level  that we know of....please add/eloborate

1. We will modify the DTD to additional elements

2. Modify the subscription package for handling these elements

Thanks in advance...