User blog comment:TimmyQuivy/Introducing the UserRenameTool/@comment-168424-20180209193229/@comment-2212553-20180210015454

According to MediaWiki, a page that is named fandyllic is automatically capitalized as "Fandyllic", however a page that is named FandYllic with a capital Y is not automatically capitalized as "Fandyllic", and thus are two completely different names. Same goes for every other namespace including names in MediaWiki. Only the second and later characters are case sensitive.

"Uncapitalized usernames - This is a legacy requirement of the MediaWiki software FANDOM runs on. In MediaWiki, all usernames start with a capital. They just do. Remember that on FANDOM usernames as a whole are case sensitive - whenever I log in I will need to make sure to capitalize the Q in “TimmyQuivy” or I’ll get an error message."