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• float
• double (converted to float)
• string
• int
• color3
• normal3
• vector2
  
• vector3
• point2
• point3
• point4
• matrix16

Katana only has four values for arbitrary attribute "scope": primitive, face, point, and vertex.  For the most part, these scope values map to the RenderMan primvar tags as follows: primitive = constant, face = uniform, point = varying, and vertex = facevarying.  Subdivision meshes support different interpolation of primvars with the "point" scope using the "interpolationType" attribute.  If geometry.arbitrary.<group>.interpolationType is set to "subdiv", the primvar will be "vertex", otherwise the primvar will be "varying".

Here is an example OpScript showing how to set an arbitrary constant color primvar:

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