Are functions like OnAnimatorIK() included in a package?

I'm learning about 3D IK and in all of the tutorials I've seen, Visual Studios autofills in OnAnimatorIK() with its parameter, but when I type it in it does not show up. I can type it in manually, but my Unity console just tells me to call me to use the code that I want to use in OnAnimatorIK(), which I can't get the real version of.

So I was wondering if those functions were a part of another package that I need to download? Going through the list the only one that I can think to try is Animation Rigging.