"Note: The only surface types that PBR materials cannot describe are transparent surfaces (refractive or not). For transparent materials, the legacy material type should be used instead."
1. Is this an inherent problem with PBR or something that is being worked on?
"In MicroStation we allow you to toggle on PBR for these materials strictly for enabling more realistic shading in Realtime using QuickVision."
2. Quickvision can handle PBR materials for transparent materials?
"When Ray Tracing MicroStation will use the material definition you see when PBR is toggled off in the material editor."
3. Raytracing engine: is this old Modo or Mstn Masterpiece engine or the new Vue Render Path Tracer?