I ask because I was playing on the outside DC Icons starter map and Icons flash attempted to attack my Lockjaw who was standing on one of the buildings with his butt end blocking the ladder. I told him you couldn't, but upon reading the errata, the bottom half and top half of stairs are considered adjacent but not the same elevation.

But I thought stairs were consisted of two full squares. The ladders are not. How does this one go?

Ladders are in fact different from stairs. All ladders do is allow a character to move onto the elevated terrain.

So would that attack be legal or not?

Sorry

No, grounded characters in the square with the ladder can not make cc attacks against elevated targets (because of the stairs anyway).

That's what I thought. It worked to my advantage because lockjaw was blocking the ladder so his flash couldn't get to my punisher with trickshot who I sat on a corner. His only ranged was Rookie Icons Bats who I neutered with Nightcrawler anyway.
gggg
gepg
gLL=
gggg

g is ground level
e is the unoccupied elevated
P is punisher
L is lockjaw
= is the ladder

That was my setup so flash couldn't get up or attack lockjaw

mmm... campy goodness.