I used them back in the 90's. They were already designed in to systems when I arrived, so I only made minor modifications to the software. And it WAS 20 years ago. Much may have changed, and much has been forgotten.
As best I remember, we just linked to a supplied library in C++. I was supporting DOS based machines, and they were dropping DOS support about that time. When I asked about information so I could write my own routines, I was told that that information was proprietary.