I see an anomaly using examples of scripts from OOUI/Widgets/Buttons_and_Switches and others on this site – not all Wikimedia wikis appear to export the “OO.ui” thing to me. On some pages var btn = new OO.ui.ButtonWidget( { ⋯ } );
(in Scratchpad) runs fine, whereas others (including those from www.mediawiki.org) produce /* Exception: TypeError: OO.ui is undefined @Scratchpad/1:10:5 */
What is the difference?