Dave Hyatt's WebCore Rendering posts:

WebCore Rendering I - The Basics
http://webkit.org/blog/114/webcore-rendering-i-the-basics/

WebCore Rendering II - Blocks and Inlines
http://webkit.org/blog/115/webcore-rendering-ii-blocks-and-inlines/

WebCore Rendering III - Layout Basics
http://webkit.org/blog/116/webcore-rendering-iii-layout-basics/

WebCore Rendering IV - Absolute/Fixed and Relative Positioning
http://webkit.org/blog/117/webcore-rendering-iv-absolutefixed-and-relative-positioning/

WebCore Rendering V - Floats
http://webkit.org/blog/118/webcore-rendering-v-floats/