It receives the filter output so far as its input. The next run is evaluated for each title of the input, removing every input title for which the output is an empty list.
Note that within the filter run, the <<.var currentTiddler>> variable is set to the title of the tiddler being processed. This permits filter runs like `:filter[{!!price}multiply{!!cost}compare:integer:gteq[5]]` to be used for computation. The value of currentTiddler outside the run is available in the variable <<.var ..currentTiddler>>.
<<.tip "Compare named filter run prefix `:filter` with [[filter Operator]] which applies a subfilter to every input title, removing the titles that return an empty result from the subfilter">>