What is a "Delve Event"?

While playing around a bit with the PoE APIs, I noticed that this URL:
https://api.pathofexile.com/league/Mercenaries
...has something named "delveEvent" set to true.

What is this "Delve Event"? The closest thing to that which I could find is the "Endless Delve" void event, which was last run in the Kalandra league.

"

Novynn wrote:

That means that the league has a Delve ladder available (sortable by depth).

Unfortunately this isn't described in the docs like it should be... though it is mostly irrelevant for third parties I suppose.
https://www.pathofexile.com/developer/docs/reference#type-League

Thanks! That helps clear it up.

Got my hopes up a little, but that makes sense, thanks for clearing it up.