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

add? 

        # Set.add?

(from ruby core)
---
    add?(o)

---

Adds the given object to the set and returns self. If the
object is already in the set, returns nil.
    Set[1, 2].add?(3)                    #=> #<Set: {1, 2, 3}>
    Set[1, 2].add?([3, 4])               #=> #<Set: {1, 2, [3, 4]}>
    Set[1, 2].add?(2)                    #=> nil

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.