Authors have been taking "wrappers" for granted, but to better embrace HTML5 and semantics they should find alternative methods to common techniques (e.g., centering layouts with auto margin).
For IE6 to play ball when using percentage (
%), authors need to float the two boxes, to relatively position them and to set a left value equals to:
100% minus the total width of both columns divided by two.
With this layout, there is no need to position the wrapper (for IE 6) and the boxes cannot get clipped.