Any domain name must contain between 2 and 63 characters before the punctuation. Upper or lowercase letters is not case sensitive, but most people sue lowercase letters. Some top level domains allow international characters such as Æ, Ø and Å, though these are encoded in a special way making the encoded domain name containing A-Z, 0-9 and hyphens. But normally a domain name can only contain the letters A-Z, the digits 0-9 and hyphen (-), in addition to one punctuation (.) used for grouping the domains in hierarchies, e.g. under .no or .com.