 Complete the following phrase:  There are three additional classes, S11, S12 and S13, for visually impaired swimmers. The lower number indicates a greater degree of impairment: class S11 swimmers are blind or nearly blind, and compete in blacked-out goggles. They each have a tapper who uses a pole or bonker to warn the swimmer that they are approaching the end of the pool. The visual classifications are based on medical classification, and not on functional mobility. One more class, S14, is for intellectually disabled swimmers. This class was not contested at the 