VDN(valid domain name) is used to check if s string is a valid domain name
A complete domain name is valid if it meets the following criteria:
- A complete domain name must have one or more subdomain names and one top-level domain name.
- A complete domain name must use dots (.) to separate domain names.
- Domain names must use only alphanumeric characters and dashes (-).
- Domain and subdomain names must not begin or end with dashes (-).
- Domain names must mot have more than 63 characters.
- The top-level domain name must be one of the predefined top-level domain names, like (com), (org), or (ca)
- unicode check