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• The new material workflows requires that the most downstream VOP node is a PxrMaterialBuilder. 
• RSL (RenderMan Shading Language) support was removed in RenderMan 21. Materials (BxDFs) are C++ constructions and patterns should be OSL when possible.
• We accept the Houdini attribute names for use in shading by connecting a PxrPrimvar or PxrAttribute node to a parameter using the appropriate name.

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