Description

   The decc$feature_set_value function sets the default value or
   the current value (as determined by the mode argument) for the
   feature specified by index.

   If this function is successful, it returns the previous value.

   On error, -1 is returned and errno is set to indicate the error.

   See also decc$feature_get, decc$feature_get_index, decc$feature_
   get_name, decc$feature_get_value, decc$feature_set, decc$feature_
   show, and decc$feature_show_all.