Key MediaWiki pages/interface parts (selected from Special:AllMessages). Use for Related Changes and generally to see where to focus attention on maintenance and improvement of MediaWiki pages.

Registration/login
The user registration screen is at Special:UserLogin/signup. The bottom bit is MediaWiki:Signupend; the top bit, only shown if you're logged out, is MediaWiki:Fancycaptcha-createaccount.
Message at the bottom of the user login screen (Special:UserLogin) is at MediaWiki:Loginend.
Message shown after successful user registration: MediaWiki:Welcomecreation.
Block messages
MediaWiki:Autoblockedtext
MediaWiki:Blockedtext
Delete messages
MediaWiki:Deletedtext
Move messages
MediaWiki:Movepagetext (shown above Move Page form, after clicking Move tab)
MediaWiki:Movepage-moved
Editpage notices
MediaWiki:Wikimedia-copyrightwarning
MediaWiki:Edittools
Other

See also

edit