Why Spock suggest no indentation after labels?

I'm wondering why Spock, in its official documentation suggests using no indentation after labels. E.g. here:

def "events are published to all subscribers"() {
  given:
  def subscriber1 = Mock(Subscriber)
  def subscriber2 = Mock(Subscriber)
  def publisher = new Publisher()
  publisher.add(subscriber1)
  publisher.add(subscriber2)

  when:
  publisher.fire("event")

  then:
  1 * subscriber1.receive("event")
  1 * subscriber2.receive("event")
}

? Is it something that comes from Groovy coding style?