From Site5Wiki

webkit.org: ongoing open source development of Apple's WebKit engine

WebKit is an open source web browser engine. WebKit is also the name of the Mac OS X system framework version of the engine that's used by Safari…and many other OS X applications. WebKit's HTML and JavaScript code began as a branch of the KHTML and KJS libraries from KDE.

— webkit.org's developers

WebKit allows you to write and debug CSS, DOM, and Javascript while using your browser, in a very fluid, comfortable manner. It does so in part using its Web Inspector element.

When you run WebKit.app, you’re actually running the shipping version of Safari with the latest version of the WebKit framework. Nothing on your system gets replaced, and you can download and run as many nightly builds as you'd like.

— Surfin' Safari blog ( feed)

• WebKit's official wiki, which includes instructions on how to build WebKit on Windows, GDK, and Linux via Qt
• WebKit's DOM Class Hierarchy; List of DOM Namespaces; and DOM File List

How WebKit Assists Webmasters

• Web Development with Safari, by Jon Hicks

• CSS: Cascading Style Sheets
• DOM: Document Object Model
• Javascript integration: Javascript
• mathematical formulas and expressions integrated into websites: MathML
• SVG integrated into websites: Scalable Vector Graphics
• XHTML: HyperText Markup Language
  • editing
  • forms
  • layout and rendering
• XML: Extensible Markup Language
• XSLT: eXtensible Stylesheet Language Transformation
• Developing for accessibility

Further WebKit Resources

• Introduction to Web Kit Objective-C Programming Guide on developer.apple: Reference Library > Guides > Cocoa > Internet & Web > Web Kit Objective-C Programming Guide (article also available as a .pdf download)
• answers.com/webkit
• GnuStep WebKit = port of WebKit to GNU

Related wiki pages: 508; CSS; DOM; JavaScript; MathML; Safari; SVG; Safari extensions, plugins and tools for webmasters; Validation; XHTML; XML; XSLT