Madras. Tennis dresses. Sailor stripes and kelly green. The Official Preppy Handbook might seem like odd reference material for Tess Giberson, but that very unexpectedness may have been the point, as the designer took on the aesthetic codes and conventions of our nation's WASP elite this season. Giberson's collection had a lot of snap: For the most part, she didn't seem to be overthinking her clothes, and you didn't need to know the conceptual background of, say, a mint silk trouser jumpsuit to comprehend the garment's appeal. Ditto the clever cape-shaped trenchcoats and Giberson's insouciantly sexy slipdresses and organza button-downs. As usual, the designer also did well with her knits, in particular those that featured a kind of knit-in, oversize perforation, and finer versions in an abstracted check pattern. A few garments did come off a little mannered, like the dresses and skirts with arcing hems. But as a whole this was a strong outing for Giberson, one marked by her ample intelligence, but not showing it off.