ResourceLoader is the delivery system in MediaWiki for the optimized loading and managing of modules, which consist of JavaScript, CSS and interface messages.

Rendered page HTML is often cached for long periods of time, which makes changing the logo harder than it should be; caching of ResourceLoader modules can be finely controlled. You can use other modules as examples, e.g. ResourceLoaderUserCSSPrefsModule and ResourceLoaderLanguageDataModule.

See this bug report for more information. Students are required to read Wikimedia's general instructions first.