# File lib/sass/util.rb, line 1016
    def flatten_vertically(arrs)
      result = []
      arrs = arrs.map {|sub| sub.is_a?(Array) ? sub.dup : Array(sub)}
      until arrs.empty?
        arrs.reject! do |arr|
          result << arr.shift
          arr.empty?
        end
      end
      result
    end