Vector property missing when translating RSL to OSL


This was originally posted in the RenderMan forum, but I think someone here might know the answer, so I'll try posting here.

I'm in the process of translating the wood BRDF from the paper Measuring and Modeling the Appearance of Finished Wood by Marschner et al. from RenderMan Shading Language to Open Shading Language.
One line reads:

  1. thOutPrime = asin ( ssOutDir.axis );

where ssOutDir is a vector and thOutPrime is a float.
The OSL compiler complains about that line, saying there is no 'axis' property of a vector, so I'm wondering what the axis property actually is equivalent to. I've scoured the docs and forums but have found no answer. Anyone who knows and can tell me?

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