Supporting formats that split data into multiple files

[marcpabst]

Hi, how should we deal with formats that use multiple different files to store data? Think of formats that consist of a data file and a header file with the metadata. It makes sense to load them together but I'm not sure if something like that is currently possible.

[timholy]

NRRD is an example. In that case we recognize the header file which has a pointer to the data file. We don't do anything with the data file. So if there's a "top level" file I think you can just add support for that format here.