Cannot find documentation for CGSGetNumberOfDisplayModes

I was looking at the code on the repo below and found that it's invoking a function named CGSGetNumberOfDisplayModes. I couldn't find any documentation for such function on my Google searches. Any ideas on where it is documented?


https://github.com/avibrazil/RDM/blob/master/utils.mm


It's a pretty trivial function, but I just would like to know where this function's documentation is located so I can look at what else is available.