A Schema Rule Set is a set of rules one can use to validate an XML Schema. For example, a rule can specify that attribute names, as defined in the XML Schema, begin with a lowercase alphabet, or that a given complex type can only be extended from a specific type.
A set of schema rules is saved in a Rule Set file, which is an XML (.xml) file. XMLSpy contains a Schema Rules Editor in which you can edit schema rules graphically. In XMLSpy, one or more Rule Set files can then be assigned to an XML Schema. The XML Schema is validated in Schema View against the assigned Rule Sets by selecting the XML | Validate (F8) command.