The decc$feature_get_index function looks up the string passed
    as name in the list of supported features. If the name is found,
    decc$feature_get_index returns a (nonnegative) index that can
    be used to set or retrieve the values for the feature. The
    comparison for name is case insensitive.

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

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