It was merged. The docs are lacking, but if you are familiar with PBR from other engines and materials in Urho, then it's simple enough. When making a material, pick one of the PBR techniques. I've only tested the metalness/roughness workflow, so in that case in the specular texture you feed a roughness (red) /metalness (green) texture. Then you use zones in Urho to provide a zone texture for image based lighting. There is an example scene you can open in the editor to see how it was done.