Creates a classification of expressions. The bin width is determined by the number set as interval. The result is shown as a<=x<b, where a and b are the upper and lower limits of the bin. The x can be replaced by an arbitrary string stated in label. 0 is normally the default starting point of the classification. This can be changed by adding an offset.
class( var,10 ) with var = 23 returns '20<=x<30'
class( var,5,'value' ) with var = 23 returns '20<= value <25'
class( var,10,'x',5 ) with var = 23 returns '15<=x<25'