Bag ID

[Rhyono]

How do the bag IDs work?

I understood these:
BAG_BACKPACK - shows items in that toon's bag.
BAG_BANK - shows items in the bank.
BAG_WORN - shows items that toon is wearing.

But didn't know what to do with these:
BAG_BUYBACK - I assumed this would show items that can be bought back but I don't know how to make it work.
BAG_GUILDBANK - I assumd this would show items in the guild bank, but I don't know how you'd choose which guild or how to make it work. I tried opening the guild bank while using it but that didn't work.
BAG_VIRTUAL - Not sure what this does.

Bonus question: what is the craft bag considered and how is its data accessed?