index

    An integer value from 0 to the highest allocated feature.

 mode

    An integer indicating which feature value to return. The values
    for mode are:

       __FEATURE_MODE_DEFVAL        Default value
       __FEATURE_MODE_CURVAL        Current value
       __FEATURE_MODE_MINVAL        Minimum value
       __FEATURE_MODE_MAXVAL        Maximum value
       __FEATURE_MODE_INIT_STATE    Initialization state