This element is used to reference a feature and define a rule for its feature classes. The rules may be defined via values, lists, intervals or feature groups in conjunction with a quantity operator.
The simple data type operator was defined for this purpose and may contain the following values:
eq (equal)
ne (not equal)
in (is contained in a quantity)
nin (is not contained in a quantity)
gt (greater)
lt (less)
ge (greater than or equal)
le (less than or equal)