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

union 

        # Set.union

(from ruby core)
---
    union(enum)

---

(This method is an alias for Set#|.)

Returns a new set built by merging the set and the elements of the
given enumerable object.
    Set[1, 2, 3] | Set[2, 4, 5]         #=> #<Set: {1, 2, 3, 4, 5}>
    Set[1, 5, 'z'] | (1..6)             #=> #<Set: {1, 5, "z", 2, 3, 4, 6}>

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.