Q: RI and isolevels

Standard (draft) says:

Regardless of the isolation level of the SQL-transaction, phenomena
P1, P2, and P3 shall not occur during the implied reading of schema
definitions performed on behalf of executing an SQL-statement, the
checking of integrity constraints, and the execution of referen-
tial actions associated with referential constraints.

I'm not sure what they exactly mean. Could someone run two tests
for me (in Oracle and Informix/Sybase)?

create table p (k integer primary key);
create table f (k integer references p(k));

session-1:
set transaction isolation mode serializable;
select * from f; -- just to ensure that xaction began -:)

session-2:
insert into p values (1);
commit;

session-1:
insert into f values (1);
--
-- Results? Abort?
--

What's the result in the case of read committed isolevel in
session-1? Is insert succeeded?

TIA!

Vadim