Why isRailties not included in standard API doc distribution

I was Googling around the other day to figure something out and in my
quest found this page:

Hmmm, I thought, that isn’t included at http://api.rubyonrails.org.
Why? I
did a little further digging, but this was all I could find (from

Unfortunately, RailTies, the Rails library which defines
generator behavior, intializer behavior, and the rails script
itself isn’t included in the distributed API [docs]…

However, no explanation is provided.

Why isn’t it included in the distributed API docs? What is the proper
way to gain visibility into those APIs?