A functionItem (DMN 1.6, 7.3.3): the type of a function, in an item definition. output_type_ref is the type of the result,
and parameters are the Dmn.Model.InformationItems that the function takes.
Summary
Types
@type t() :: %Dmn.Model.FunctionItem{ id: String.t() | nil, line: pos_integer() | nil, output_type_ref: String.t() | nil, parameters: [Dmn.Model.InformationItem.t()] }