Enable WAN down browser redirect notice

[wouterv]

RT-N66U with 3004.376.3657 firmware.
I noticed this option under Advanced Settings>Administration>System: "Enable WAN down browser redirect notice", enabled by default.
See picture below.
I do not see any result, e.g. at manual disconnect from WAN and trying to open some web page, I would expect an "Asus router page" telling me the WAN is down.
What should it do?

 

[wouterv]

Hmm...is it intentional or brought in unintented from code for an other product:

ASUS DSL-AC68U Firmware version 3.0.0.4.376_2139 (This product supports both Annex A and Annex B)
....
11. Now supports "Enable WAN down browser redirect notice" feature(Advanced Settings > Administration > System).

 

[Nullity]

Maybe it only gets triggered when the WAN port is connected but the gateway link is down?