Visualize the first responder?

Question

Is there any AppKit debug option NSDocument// NSApplication, a debug flag, or another third-party extension to render the current one firstResponderfor any given instance NSWindowin the current application?

We are creating a single-window application that dynamically loads and replaces views in and out of a window, and tracking / debugging the current one firstResponderbecomes a pain in the neck.

Any hints / practices are greatly appreciated!