What does the property "TreatAsDesktopFullscreen" exactly do?

[Aetopia]

I have been poking around the source code of WindowInvestigator and was wondering what does "TreatAsDesktopFullscreen" exactly do?

[dechamps]

According to my reverse engineering notes, the internal DesktopFullscreenHelpers::IsValidDesktopFullscreenWindow() will return true if:

(
  GetWindowBand() == 1 &&
  GetPropW("NonRudeHWND") == 0 &&
  GetPropW("LivePreviewWindow") == 0 &&
  IsShellManagedWindow() == 0
) || GetPropW("TreatAsDesktopFullscreen") != 0

So I'd intuitively expect it to behave as the opposite of NonRudeHWND - as in, TreatAsDesktopFullscreen can be used to force a window to be considered "rude".

This is only my recollection from rough notes I took at the time though, so please take this with a grain of salt. In order to confirm the above I would need to dig into the binary code again, which I'm not going to do because it would take me a long time to refamiliarise myself with it since I last looked at this more than a year ago.

[Aetopia]

Thank you!