The Web Inspector is a tool that allows you to view information about CSS styles, DOM hierarchy and more in a compact floating window. More information about the Web Inspector can be found here.
Safari includes a develop menu that contains some tools that may be useful to web developers. The Develop menu can be enabled in Preferences under the Advanced tab.
- Working with the WebKit Nightly Builds Includes information about changes to the <script> and <canvas> tags.
- Object detection ADC article on alternatives to browser sniffing.
- XMLHttpRequest in Safari ADC article on using the XMLHttpRequest object. Includes examples.
- Web Page Development: Best Practices ADC article suggesting some best practices for web development.
- Extensive list of common user agent strings (Wikipedia)
- css-discuss Active mailing list and extensive wiki.
- Serving XHTML as text/html Ian Hickson's article on the dangers of serving XHTML as text/html.
- Web design references Links about every topic imaginable.
- CSS 2.1 Spec When all else fails, consult the spec.