What is the size limit for a varchar2 PL/SQL subprogram argument in Oracle?

When you create a procedure (or a function) in Oracle PL/SQL, you cannot specify the maximum length of the varchar2 arguments, only the datatype. For example

create or replace procedure testproc(arg1 in varchar2) is
begin
  null;
end;

Do you know the maximum length of a string that you can pass as the arg1 argument to this procedure in Oracle ?