PLC: V and Z registers vs. D registers

Hi, I'm converting a A2S PLC to a Q02UDE PLC. And I've came over some registers I'm not used to program with:

1. What is the difference between V-register (edge relay) and D-register (data register)?

2. What does H0V mean?

3. What is the difference between Z-register (Index register) and D-register (data register)?

Thanks for the help.