Oracle Unique Constraint with Expression

Does Oracle support constraints with expressions like so?

Notice Z = 'N'

ALTER TABLE A ADD CONSTRAINT U_A_KEY UNIQUE(X,Y,Z = 'N');

Is this Unique constraint possible?

Example:

INSERT INTO A VALUES('X','Y','N');  --OK
INSERT INTO A VALUES('X','Y','Y');  --OK
INSERT INTO A VALUES('X','Y','Y');  --OK
INSERT INTO A VALUES('X','Y','N');  --VOLIATION