More than one "infraAttrGroupRef" for a track

Bob Janssen (Siemens Netherlands) mentioned in the forum that it would be fine if a track referenced more than one infraAttrGroup in order to separate various infraAttrGroups by their functionality (e.g. electricity, speed, etc.).

That is a good idea and therefore, we suggest to create a new sub-element infraAttrGroupRefs for the track element. This is a container for an arbitrary number of infraAttrGroupRef instances.