VisualEditor

VisualEditor is the WYSIWYG editing component of MediaWiki. VisualEditor contains browser-side component that works in tandem with a server-side called "Parsoid". The basic architecture of MediaWiki's VisualEditor infrastructure

Browser                Server                 Server VisualEditor           Parsoid                Database Wikitext DOM <-->  Wikitext DOM converts to                        Wikitext      <--> Wikitext

The Wikitext DOM is an annotated HTML that makes it possible for clean roundtripped changes to the Wikitext. Thus, diffs to changes in Wikitext are reasonably easy to read.