relating to this page, I think we could be more specific.
According to my tests, it seems the World Ambient Occlusion is the equivalent of adding an ambient occlusion node in the existing material and mixing it with the diffuse node using an “Add Shader” and doing so in every material that includes a diffuse (but only mixing with the diffuse).
Side note : it becomes impossible to get the same result with shaders when using a Principled BSDF that is partially diffuse and partially something else that the World Ambient Occlusion doesn’t take into account (e.g. Metallic, SSS, transmission).
Is this interpretation right ?