It prohibits: "...ripped jeans, high cut Bermuda or beach shorts, swim wear, athletic singlets, cycling shorts, flip flops or thong sandals, dirty or unkempt clothing." Furthermore "Any extremes of personal presentation are prohibited as are bare feet and exposed midriffs"
Theres the quote off that website link- although I've never had any problems going in and it was only by chance that we went in- we didn't dress formally or anything!