v2
The syntactic constraints on a domain name are taken from Wikipedia: Domain Name, excerpted here for ease of reference.
The syntactic constraints on a domain name are taken from Wikipedia: Domain Name, excerpted here for ease of reference.
Wikipedia
Domain names may be formed from the set of alphanumeric ASCII characters (a-z, A-Z, 0-9), but characters are case-insensitive. In addition the hyphen is permitted if it is surrounded by characters, digits or hyphens, although it is not to start or end a label.
The hierarchy of domains descends from the right to the left label in the name; each label to the left specifies a subdivision, or subdomain of the domain to the right. For example: the label example specifies a node example.com as a subdomain of the com domain, and www is a label to create www.example.com, a subdomain of example.com. This tree of labels may consist of 127 levels. Each label may contain from 1 to 63 octets. The empty label is reserved for the root node. The full domain name may not exceed a total length of 253 ASCII characters in its textual representation. In practice, some domain registries may have shorter limits.
Domain classes related to countries