in reply to Hash key composition with a comma?

It may have been a nice idea back then but you really should eliminate all such things from your code today.   Because, sooner or sooner, your actual-data is going to include an instance of that "separator" and ... congratulations, you've just been waked-up at three o'clock in the morning when your pager went off, and ushered into Debugging Triage Hell. When you encounter such logic, it should be promptly refactored into a HoH = Hash of Hashes re-implementation.