void set_value_in_list(bool val, bool ok_if_empty);

WARNING! This method has been deprecated in PHP-GTK 2 and should NOT be used in newly written code.

Specifies whether the value entered in the text entry field must match one of the values in the list. If this is set then the user will not be able to perform any other action until a valid value has been entered.

If an empty field is acceptable, the ok_if_empty parameter should be true.