We are suing RFA 8.1 C++ api and MarketPrice(MP) domain to get Level1 data. Reuters data model suggest that Field BOOK_STATE(FID - 6516) is "compatible" and show it to be "Optional". What does it mean? It will be available on certain markets only? if so, can I know which markets publish this field?
Also as shown in Red circle, clicking mouse over "<<" suggests that "field is backward compatible". What does that mean?