docs: function internal_download_task(center, taskId) {
  	// taskDef is obj, decoded and distributed
  	function cached_as_promise(taskDef) {
  		return GLOBAL_CACHED_TASKS[this] = Promise.resolve(taskDef);
  	}
  	return GLOBAL_CACHED_TASKS[taskId] || Promise.resolve(center.download_task(taskId))
  		.then(distributed_task.bind([this, taskId]))
  		.then(cached_as_promise.bind(taskId));
  }