Anything Else The Subcodes of European Region 2 DVDs

[mediafox]

European Region 2 DVDs can be subcoded:

D1: United Kingdom only
D2 + D3: Europe except United Kingdom and Ireland
D4: All of Europe

I have some questions about that:

1. What exactly is the difference between D2 and D3?
2. Where is this additional code saved (The ordinary region code is in the file "VIDEO_TS.IFO" [table "VMGM_MAT"], byte offset 35 decimal (23 hex)? How can it be edited?
3. How does the DVD check this additional code?
4. Is it possible to add subcodes to other Region DVDs, so that e.g. a Region 4 DVD plays in Australia / New Zealand, but not in Latin America?
Can DVDs be "country-locked" like Blu-ray discs?

[fengtao]

There is no country-locked feature for DVD.