An RWUCollationKey stores preprocessed comparison information for a Unicode string, and can be used to speed repeated string comparisons; for example, when sorting a set of strings. The RWUCollator class calculates collation weights incrementally. This ensures good performance, as most strings differ in their first few characters. However, if string comparisons are to be made repeatedly, then best performance can be achieved by obtaining an RWUCollationKey for each string and comparing the keys.