I'll post the tweet:
Ryan Block posts an image of a popup dialog. At the top is the word "cancel" to the left and an x to the right in a grey box; this would presumably be to remove the popup entirely and cancel whatever action caused it.
The message text says:
Are you sure you want to cancel this action? Click 'OK' to cancel the current action or 'Cancel' to continue.
The buttons presented are OK and Cancel.