def identifier(key)
      key &&= key.to_sym
      return unless Rudy::ID_MAP.has_key?(key)
      Rudy::ID_MAP[key]
    end
def identifier(key)
      key &&= key.to_sym
      return unless Rudy::ID_MAP.has_key?(key)
      Rudy::ID_MAP[key]
    end
Returns the string identifier associated to this +key+