From Tapestries MUCK
Returns the sorted contents of list. If 4 arguments are given, then it evaluates expr with a pair of values, in var1 and var2.
If expr returns true, then it will swap the positions of the two values in the list. It runs this comparison on every pair of items in the list, so it will be evaluated N*N times, where N is the number of items in the list.
This method can also be used to randomize a list.