void set_insert_mode(bool im);
If invoked with true, the edit mode is set to insert (entering a character in the middle of a string will insert it, and not overwrite the next character). If invoked with false, the edit mode is overwrite. Note that the user is capable of changing this state by pressing the insert key, and that this change will be saved for the next inputs to the stream. The default value is true.
gstream-get_insert_mode(3), gstream-insert(3), gstream-overwrite(3).