The <<.op :then>> filter run prefix is used to replace the result of all previous filter runs with its output.
If the result of all previous runs is an empty list, the <<.op :then>> prefixed filter run is not evaluated.
If the output of a <<.op :then>> prefixed filter run is itself an empty list, the result of all previous filter runs is passed through unaltered.
<<.tip "Note that a list with a single empty string item is not an empty list.">>
!! <<.op :then>> run prefix versus the <<.olink then>> operator
The major difference between the <<.op then>> operator and a <<.op :then>> prefixed filter run is that the operator will replace //each item// of the input [[Title List]] with its parameter while <<.op :then>> will replace the //whole input list// with the result of its run.
|^<<.operator-example m1-1 "[tag[WikiText]] :then[[true]]">>|^<<.operator-example m1-2 "[tag[WikiText]then[true]]">><p>To make them equivalent, additional filter steps may be added:</p> <<.operator-example m1-3 "[tag[WikiText]count[]compare:number:gt[0]then[true]]">>|