Where is nominatim adress keys list?

The example request:

http://nominatim.openstreetmap.org/reverse?format=json&lat=45.468401928178&lon=9.1730680478755&accept-language=en

Answer:

{
    ...
    "address" : {
        "cafe" : "Fiorio 1780",
        "house_number" : "26",
        "road" : "Via Vincenzo Monti",
        "suburb" : "Porta Vercellina",
        "city" : "Milan",
        "county" : "Milan",
        "state" : "Lombardy",
        "postcode" : "20123",
        "country" : "Italy",
        "country_code" : "it"
    },
    "boundingbox" : ["45.4681247", "45.4683247", "9.172875", "9.173075"]
}

The address keys are: cafe, house_number, road, suburb, city, county, state, postcode, country, country_code.

I want to find the list of all available address keys. If this list doesn't exists, I want to know relation between this keys and osm tags.