available
The handles for name that no inbox holds, the name itself first. name is a handle as a user typed it; its ASCII capitals become lowercase. A name with a code checks only that handle. A name without a code checks itself and 100 random codes in one lookup. Text outside the handle grammar fails with InvalidArgument, before any request. The SDK applies no other rule, so a claim of a returned handle can still fail with HandleNotAllowed. An unregistered client can call it.