<<.from-version "5.3.0">> The <<.op function>> operator applies a named [[function|Functions]] to the input titles, and returns the results from the function. The function is invoked once with all of the input titles (in contrast, the [[filter Operator]] invokes its function separately for each input title).
The first parameter of the <<.op function>> operator specifies the name of the function to be called. Subsequent parameters are passed to the function.
The mapping between the parameters is //positional//, with each consecutive parameter specified in the function call mapped to the corresponding parameter in the function definition. Any parameters that are not provided are given their default values.
<<.tip "Compare with the similar [[filter|filter Operator]] and [[subfilter|subfilter Operator]] operators which take a filter strings as their parameter instead of a named function, and does not permit parameters to be passed">>