[Plugin: NextGEN Gallery] Where to find developer's documentation and APIs?

I’m struggling all the day looking for NextGEN Gallery complete documentation for developers or, more in general, some APIs documentation.

Looks like there is nothing like that.

Considering the huge amount of people using it, I’m surprised that there is no documentation, but just some sparse post about specific issues that mentions some specific function.

Maybe I’m just looking in the wrong way?