Can this be changed to something slightly more descriptive like ``array_names`` or ``data_names`` or similar?  I know you have it as private, but anyone wanting to subclass will need to implement it, so it *can't* be private.

@astrofrog or @Cadair, does the use of `_names` seem fine to you?  Or was there some other way you had in mind for how to sniff out the names of the data attributes?