This is a Ruby tree! It shows every object from the Ruby Programming Language in a tree format.

< 

        # Module.<

(from ruby core)
---
    mod < other   ->  true, false, or nil

---

Returns true if *mod* is a subclass of *other*. Returns `nil` if there's
no relationship between the two. (Think of the relationship in terms of
the class definition: "class A < B" implies "A < B".)

This is MURDOC! A Ruby documentation browser inspired by Smalltalk-80. It allows you to learn about Ruby by browsing through its class hierarchies, and see any of its methods.