def within(&block)
      raise ArgumentError if block.nil?
      Within.new(block, broker)
    end
def within(&block)
      raise ArgumentError if block.nil?
      Within.new(block, broker)
    end
Use for starting temporary subscriptions.
 {http://railseventstore.org/docs/subscribe/#temporary-subscriptions Read more}

 @param block [Proc] block of code during which the temporary subscriptions will be active
 @return [Within] builder object which collects temporary subscriptions