Avoid mixed case in URLs.
All lower case is preferred for readability.
URLs on certain UNIX servers are case sensitive and will not work unless the Use relative URLs for portability. A properly configured suite of pages linked with relative URLs can be moved from one location to another with a minimum of reconfiguration. Use HTML extensions sparingly. Certain elements such as the center tag are relatively silent when viewed with a non-compatible browser. Other elements such as tables will be unintelligible.