Both Eric Meyer and Dave Shea and Molly Holzschlag discuss ways of using relatively positioned elements as "containers" or "wrappers" for other elements. Remember, the absolutely positioned element is positioned according to its containing block: the closest ancestor element that has been positioned. If there is no positioned ancestor element, the containing block for the absolute element will be the page itself (i.e., html).
Using a relatively positioned containing block, you can absolutely position an element within another element rather than within the page itself, and you can create a centered layout with a fixed width much more easily than with absolute positioning alone. Designers have begun using relatively positioned containing blocks that are centered on the page by setting the left and right margins at auto; these relatively positioned boxes can then contain other elements, both positioned and unpositioned.
Absolute and relatively positioned elements can be combined within the relatively positioned containing block. The resulting designs are centered on the page, usually with repeated background images placed within the body, while the content and navigation portions of the page have solid backgrounds that make them stand out against the background patterns.