I don't know what Mirror is. But this was so cool. How did you get this? The WSJ article I posted is behind a paywall.
Not the original poster, but a mirror in the context of websites usually means a backup copy of a piece of content that is accessible from another source.
You can archive most site on the internet on archive.is for free.
Most of the time, archive.is can defeat the paywall and save a copy of what you see for ever.
As a matter of fact, I think people should directly post archive.is links on HN instead of the original.