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

attr 

        # Module.attr

(from ruby core)
---
    attr(name, ...) -> array
    attr(name, true) -> array
    attr(name, false) -> array

---

The first form is equivalent to #attr_reader. The second form is
equivalent to `attr_accessor(name)` but deprecated. The last form is
equivalent to `attr_reader(name)` but deprecated. Returns an array of
defined method names as symbols.

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.