[Traits] Subclassing nested container types.

Is there a way to subclass composite types of container traits and
keep all the validation intact?  That is, right now, I have a trait
that I initialize in the class as "List(Tuple(Int,Int))", that is, it
must be a list of 2-tuples that contain only integers.  I would like
to add an extra step of validation, though, that constrains
specifically what set of integers are allowed in the tuples, as well
as (maybe) the length of the list.  My natural thought was to make a
subclass of the List trait, but is there any way to subclass it that
will retain the checking for 2-tuples of only int type?