Duck typing requires the primitives of the properties to also be typed. This is a building block you must built to build up to duck typing. I'm also unsure how

Duck typing requires the primitives of the properties to also be typed. This is a building block you must built to build up to duck typing. I'm also unsure how you would represent a "list of list of errors" succintly without calling it just that. A list of a list of errors. An `Error[][]`. How would "duck typing" as you describe make this type somehow less complex?