So I want to use this in my mod but there is no documentation. How am I supposed to use it now?

Additionally, the API page on the wiki is private. https://github.com/Virtuoel/Pehkui/wiki/Mod-Developer-API

It's still private after half a year, could it be finally made public?

@Virtuoel Any update on better documentation at all?

This is still a problem

After 2 and a half years, there still isn't any documentation. Not even one line of documentation! Please do something about this @Virtuoel. We need to at least know how to import the mod.

This is getting ridiculous. Are we just supposed to figure out how to use this on our own through experimentation?

In the meantime you can look at how other mods do it. An example for Fabric would be Extra Origins' modify size power.