How about default/constraint being applied to varray/nested_table elements

Question

Hi, I know that varrays and nested tables can themselves be defaulted by means of a no-arg constructor. Ok.
But what about their elements ? E.i:
create type Document_type as object ( foo VARCHAR2(10), bar NUMBER);
create type Document_array as VARRAY(10) of Document_type;
create type Document_table as TABLE of Document_type;
create table Documents (
ar Document_array DEFAULT Document_array(),
tb Document_table DEFAULT Document_table()
nested table tb store as Documents_nt;
The point is: how can I default/constrain the "foo" and "bar" elements for both the nested array and table ?
Perhaps I can work on the table Documents_nt, but the array remains out anyway.
Thanks for any help.

Answer 1

Even more:
create type DocumentRef_array as VARRAY(10) of REF Document_type;
create type DocumentRef_table as TABLE of REF Document_type;
create table Documents (
arr DocumentRef_array DEFAULT DocumentRef_array(),
tbr DocumentRef_table DEFAULT DocumentRef_table(),
How can I constrain array/table elements to be scoped or referring to a specific table, as for normal reference integrity ?