UTF-8, Utf-8, or utf-8?

[Dan Jacobson <jidanni@jidanni.org>]

For the locales stuff, should I use
zh_TW.UTF-8, zh_TW.Utf-8 or zh_TW.utf-8?
My guess is the latter, from locale -a.
Should I report bugs if I see mentioning of the others?
How about for web pages? charset=utf-8 like tidy or UTF-8 like Google?