OptionalallowOptionalrejectIf specified, this function is called to filter values before they are added to the window. If the reject function returns true, the value is NOT added.
If the 'allow' function is also specified, it only gets used if 'reject' returns false.
How many values to keep
If specified, this function is called to filter values before they are added to the window. If the allow function returns true, the value IS added.
If 'reject' is also specified and it returns true, the allow function will not override it.