I noticed in the latest ECMAScript 5 spec that Date's toJSON is defined to
return the same string as Date's toISOString. (as of:
candidate-draft-tc39-2009-025_errata-5-19)

Does this mean that toISOString should now be defined to return "null" for NaN
dates, or that the strict 1:1 correspondence between toISOString and toJSON
should be relaxed?

I'm sorry to keep raising the issue of NaN dates, it's truly not all I think
about, I just don't want to head into our bold new scriptalicious future with
wiggle room for implementors.