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The Physically Based Shading Nodes you use in your MaterialX graphs are all converted to PxrSurface and then passed to RenderMan.  PxrSurface can represent most of what MaterialX defines.  Because each renderer is different, the picture you get from RenderMan with a given MaterialX network may vary from the picture you get from another renderer with the same network.  One limitation that currently exists is that we don't support material layering via MaterialX.

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