Applying Ambient occlusion using a decal projector. Is this possible?

Hi, all!
I was reading through Unity's blog document on "Setting up HDRP environment,"
And it says that baked ambient occulusion map (achived in DCC package)
can be applied to the mesh using a decal projector.
(NOT SSAO or any other realtime techniques. as mentioned in the document.)

Until now, I thought that decal projector is just like a sticker
(a totally separate thing from existing meshes in the scene.),
so I was intrigued once I heard this approach.

But Its very hard for me to find right document, or tutorials using technique.

any information that could help
to shed some light on this matter would be greatly appreciated.


thanks!

(I have attached information that I saw in the blog post.)