In general, only the following characters may be used in a domain name:

• Letters a through z (no accents of any kind will be accepted). Note that domain names are not case sensitive. This means there will be no distinction made between upper case letters and lower case letters (A = a);
• The numbers 0, 1, 2, 3, 4, 5, 6, 7, 8 and/or 9
• The hyphen character

There are limits on how you can use hyphens:

• A hyphen cannot be used to start or end a domain name
• Two or more hyphens cannot be in consecutive positions

Domain names must:

• Be at least 2 or 3 characters long, dependant on the namespace, EXCLUDING the namespace. For example:
  • z.com is invalid as the length of the domain without the namespace (.com) is only 1 character
  • yes.com is valid as yes is at least 2 characters long
• Be no more than 63 characters EXCLUDING the namespace
• Contain only letters, digits, and hyphens. For example:
  • It's-1-Bad-Domain.com is invalid as it contains illegal characters
  • its1gooddomain.com is valid as it does not contain illegal characters
  • its-1-good-domain.com is also valid as it does not contain illegal characters
• Not start or end with a hyphens. For example:
  • -1-bad-domain.com is invalid as it begins with a hyphen
  • 1-bad-domain-.com is invalid as it ends with a hyphen
  • bad--domain.com is invalid as it contains consecutive hyphens
  • 1-good-domain.com is valid as it does not begin or end with a hyphen