docs: function Sequence (opts) {
      if (opts.actions) {
          return initWithActions(Object.getPrototypeOf(this).constructor, opts.actions)
      }
  
      if (!opts.one) {
          throw "Sequence argument one must be non-nil"
      }
      if (!opts.two) {
          throw "Sequence argument two must be non-nil"
      }
      this.actions = []
  
      var d = opts.one.duration + opts.two.duration
  
      Sequence.superclass.constructor.call(this, {duration: d})
  
      this.actions[0] = opts.one
      this.actions[1] = opts.two
  }