The decc$feature_set function allows you to call the
    decc$feature_set_value function with a character-string feature
    name, rather than an index into an internal C RTL table.

    If successful, the function returns the previous value.

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

    See also decc$feature_set_value, decc$feature_get, decc$feature_
    get_index, decc$feature_get_name, decc$feature_get_value.
    decc$feature_show, and decc$feature_show_all.