%

        # Range.%

(from ruby core)
---
    %(n) {|element| ... } -> self
    %(n)                  -> enumerator

---

Iterates over the elements of `self`.

With a block given, calls the block with selected elements of the range;
returns `self`:

    a = []
    (1..5).%(2) {|element| a.push(element) } # => 1..5
    a # => [1, 3, 5]
    a = []
    ('a'..'e').%(2) {|element| a.push(element) } # => "a".."e"
    a # => ["a", "c", "e"]

With no block given, returns an enumerator, which will be of class
Enumerator::ArithmeticSequence if `self` is numeric; otherwise of class
Enumerator:

    e = (1..5) % 2 # => ((1..5).%(2))
    e.class        # => Enumerator::ArithmeticSequence
    ('a'..'e') % 2 # =>  #<Enumerator: ...>

Related: Range#step.