Domain names are case-insensitive, which means that computers take upper- and lower-case letters to mean the same thing. As such, it may be desirable to style domain names with proper title case, or use letter case to distinguish between words in concatenated multiple-word domains. This convention has been in practice since the early days of the DNS, for example with the domains Sun.COM or Berkeley.EDU. Just bear in mind that it's less effort for an individual to type in all lower-case letters.

The caveat here is that URIs containing these domain names cannot be guaranteed to be normalized by other systems before being stored or compared. Therefore, if you choose to do style your domain names any way other than with all lower-case letters, be sure to make it consistent across the board in all references on all pages and other material. It is also possible to redirect supplied all-lower-case URIs to correctly cased ones.

This recommendation currently requires more research. It may be amended or reversed in the future.