Characters allowed in a domain name

A domain name can be composed of the following characters:

1. Alphanumeric Characters: This includes all the letters from A to Z (case insensitive) and numbers from 0 to 9.

2. Hyphen (-): A domain name can include a hyphen, but it cannot begin or end with a hyphen.

3. Period (.): This is used to separate the different levels of a domain name. For example, in the domain name "www.example.com", the periods separate "www", "example", and "com".

It's also important to note the following rules:

• Domain names are not case sensitive. This means that "Example.com", "example.com", and "EXAMPLE.COM" are all considered the same domain name.

• The total length of a domain name cannot exceed 253 characters in its textual representation (including the periods that separate different parts of the domain name). In the DNS protocol, which is used for domain name resolution, the maximum length is 255 octets of binary data.

• Each label (the part between the dots) of a domain name must be between 1 and 63 characters long.

• Internationalized Domain Names (IDNs) can include characters from non-Latin scripts (like Arabic, Cyrillic, Chinese, etc.) encoded using Punycode into the allowed character set. These are typically used to support domain names in the native languages of non-English speaking regions.

Remember, these are the technical rules for what characters can be included in a domain name. There may be additional rules or restrictions imposed by individual domain registrars.