ISO 10545-13 exposes tiles to household chemicals, swimming-pool salts, and acids and alkalis at low and high concentration, and classes the visible effect from A (none) to C.
ISO 10545-14 applies staining agents and records how they can be removed. Class 5 means hot water is enough; lower classes need detergents, abrasive cleaners or solvents, and class 1 means the stain could not be removed.