Template:Map Features:addr extra
More detailed information as approved here: Proposed features/addr keys (2011-04)
|Tags for parts of a building
|The door number (or name) of an apartment/flat/office/room. Could also be called differently in some countries (In Austria for example it is sometimes referred to as "Top"). If a room has more than one door, you can tag them separately.
See also: room=*
|The number, letter, or name of a single unit or flat that exists within a larger complex. While a big building could have only one entrance, sometimes the way inside divides into different units or staircases, where certain apartments/flats/offices can only be reached through a specific unit. Useful for apartment, suite, or office numbers. Information necessary for postmen, for example.
In the United States, there is no consensus on how to represent secondary unit designators, however according to taginfo it is far more popular to omit the designator and only include the identifier: there are only a few thousand "Apartment/Unit/Suite A" entries versus 46,000 "A" entries as of 2021. This practice only allows data consumers to format the unit as "#A", which the USPS says will result in rejected mail in some cases.  Consider using addr:full=* to disambiguate.
|A list of flat numbers accessible in a building or behind a door.
|The floor number that is part of the address of an apartment/flat/office. Also add level=*, which is applicable regardless of whether the floor number is part of the address.
|The city block, if part of the address. Note that this tag is most often used in places where blocks can have names and not just numbers, and in many cases is specified in addition to a street name. This tag is common in a variety of countries, including India, Egypt, and Kuwait. addr:block_number=* on the other hand is common in Japan, where blocks are typically numbered and often are specified instead of a street name.
|The city block, if part of the address. This version of the tag is used in Japan, where it is common for house numbers to be associated with blocks where a street does not have a name. These blocks are typically numbered, hence the name. See JA:住所 § 街区 Block number address systemについて. addr:block=* is semantically different in that it may describe blocks that have names rather than numbers, and is not as commonly used in Japan.