Supporting arrays in Dataset

We want the ability to add small supporting arrays that accompany the main array in a Dataset. I'm not sure how we would convey to someone unaware of the contents of a Dataset that this Dataset has other supporting information.

Band Excitation would be one example where the dataset comes with multiple supporting information such as the frequency bins, excitation waveform, etc. We won't need to access this information as Dataset objects themselves. However, it would be good to track this provenance / metadata at the Reader level. Once these are written to disk and read back, we can keep just the core information if need be or continue to read all these ancillary datasets as well into memory if it makes sense.