The the t_value record in the APEX_SESSION_STATE package uses the following data type constants.

subtype t_data_type is pls_integer range 1..11;

c_data_type_varchar2      constant t_data_type := apex_exec.c_data_type_varchar2;
c_data_type_clob          constant t_data_type := apex_exec.c_data_type_clob;