Where is the documentation on RVK's?

I tried looking in the documentation on blender.org and couldn’t find any info on RVK’s. Maybe I just missed it, I don’t know.

I have a face I want to animate, and from the posts I have read bones are ok for some things - but RVK’s better for others.

I’m coming from the place of not even knowing what the heck an RVK is.

<EDIT>I just looked at Hos’s Sticky post on getting ahead in animation and noticed the RVK links. I’ll try checking there first.</EDIT>

just after lattice animation section (look for the filmstrip with the spaceship) there is a section on vertex keys, followed by a section on relative vertex keys