This structure contains UDF expression information:
old_exps: At the instantiation, they can be obtained from
the UDF feature definition by calling the public API
routine UF_MODL_init_udf_insert_data_from_def().

At the editing, they can be obtained from the UDF
instantiated feature by calling the public API routine
UF_MODL_ask_instantiated_udf().

new_exp_values: They can be inputted by the user for both of
instantiation and editing.