code: func (pq *txPriorityQueue) Pop() interface{} {
  	n := len(pq.items)
  	item := pq.items[n-1]
  	pq.items[n-1] = nil
  	pq.items = pq.items[0 : n-1]
  	return item
  }
docs: // Pop removes the highest priority item (according to Less) from the priority
  // queue and returns it.  It is part of the heap.Interface implementation.