Blue border appearing around NSScrollView

I'm sure this is normal and I'm just misunderstanding something, but since making one of my NSScrollViews slightly inset from the bottom of the window (as opposed to taking the full height), a blue border has appeared around it.

I've set NSNoBorder on the scroll view, so this must be something else.

[scrollView setBorderType:NSNoBorder];

Any pointers would be greatly appreciated. I'd like the border to go away as it 开发者_高级运维spoils the look of the app and just looks broken.

I assume it's the scroll view. The view inside it as an NSOutlineView, so maybe it's something on that?

That's the focus ring. It shows which view is going to get the keystrokes if the user types anything. If you suppress it, then your app will not be in compliance with the UI guidelines.