halfDir?

What is the fixed3 “halfDir” parameter found on some shaders (such as Mobile/Bumped Specular)?
It seems to be undocumented ( Unity Manual as opposed to Unity Manual )

I didn’t look at the “Mobile/Bumped Specular” source code, but I assume it’s the halfway vector.

Agree with Peter77. Use of the halfway vector is explained at, e.g. Cg Programming/Unity/Brushed Metal - Wikibooks, open books for an open world

Thanks for the help. I did eventually find a little documentation for it on Unity’s site, although not by that name (“halfasview”).