A Seq of ReferencRegions, pre-partitioned by their referenceNames. So, for a given pair (x, regs) in this Seq, all regions R in regs must satisfy R.referenceName == x. Furthermore, all the x's must be valid reference names with respect to the sequence dictionary.
Creates a multi-reference-region collection of NonoverlappingRegions -- see the scaladocs to NonoverlappingRegions.