===

        # Range.===

(from ruby core)
---
    self === object ->  true or false

---

Returns `true` if `object` is between `self.begin` and `self.end`.
`false` otherwise:

    (1..4) === 2       # => true
    (1..4) === 5       # => false
    (1..4) === 'a'     # => false
    (1..4) === 4       # => true
    (1...4) === 4      # => false
    ('a'..'d') === 'c' # => true
    ('a'..'d') === 'e' # => false

A case statement uses method `===`, and so:

    case 79
    when (1..50)
      "low"
    when (51..75)
      "medium"
    when (76..100)
      "high"
    end # => "high"

    case "2.6.5"
    when ..."2.4"
      "EOL"
    when "2.4"..."2.5"
      "maintenance"
    when "2.5"..."3.0"
      "stable"
    when "3.1"..
      "upcoming"
    end # => "stable"