Missing Renderman Block in Shader Mixer? (PxrFacingRatio)

ZaeZodTheToonCrafter

I've gone through the list of blocks from Renderman in the Shader Mixer multiple times and not found PxrFacingRatio (https://renderman.pixar.com/resources/RenderMan_20/PxrFacingRatio.html). It isn't exactly a new thing to Renderman, as best as I can tell, so shouldn't it be in Daz's copy of Renderman? Why can't I find it? If it isn't there at all, how would I go about adding it (or could a more experienced person do it)?