Even after Googling I can't find the answer: what would you show then at the boarder? On their website, the "share code" seems to only be for non-governmental use.

Is your passport number then linked to the visa? What happens if you get a new passport? Does it work for non-biometric passports?

Or is there some kind of stable "citizen" identifier in the passport that the visa is linked to? I can't imagine it being a simple name + DoB lookup.