You're doing two separate sorts. Which sorts by the first criteria and then resorts by the second criteria (completely ignoring the first).
No, that's not true. His first (last executed) sort code block is wrong, but in a modern perl, i.e. one with a table sort, the concept is valid: you can sort items according to one field, while keeping items that compare to the same value in their original order. Just like sgifford shows in Re: Sorting on Exists.

In reply to Re^2: Sorting on Exists by bart
in thread Sorting on Exists by ropey

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