gdk:device-pad-feature-group (pad feature index)

pad -- a gdk:device-pad object
feature -- a gdk:device-pad-feature value with the pad feature to get the group from
index -- an integer with the index of the feature to get the group from

The integer with the group number of the queried pad feature.

Returns the group the given feature and index belong to, or -1 if feature/index do not exist in pad .