Domain name syntax:
A domain name consists of one or more parts, technically called labels, that are conventionally concatenated, and delimited by dots, such as example.com.
* The right-most label conveys the top-level domain; for example, the domain name www.example.com belongs to the top-level domain com.
* 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 subdomain of the com domain, and www is a subdomain of example.com. This tree of labels may consist of 127 levels. Each label may contain up to 63 ASCII characters. The full domain name may not exceed a total length of 253 characters.In practice, some domain registries may have shorter limits.
* A hostname is a domain name that has at least one associated IP address. For example, the domain names www.example.com and example.com are also hostnames, whereas the com domain is not. However, other top-level domains, particularly country code top-level domains, may indeed have an IP address, and if so, they are also hostnames.
