SharePoint out of the box data validation for fields usually restricts the range of values allowed. Frequent request is to compare between fields in the list, e.g. field A < field B. This is a good idea when field A is start date and field B is end date, in such a case we would expect StartDate <= EndDate. So far the way to implement such a constraint was by writing custom code. But no more.
SPListConstraint just got a new feature “Data Validation Contraint” which do just that – enforce relation between the values of two columns. The feature allows more than a single constraint set on a list so there’s not problem adding few rules (A <= B, B > C, etc..). The new feature is configured using the SPListConstraint settings page: