code: func (s items) find(item Item) (index int, found bool) {
  	i := sort.Search(len(s), func(i int) bool {
  		return item.Less(s[i])
  	})
  	if i > 0 && !s[i-1].Less(item) {
  		return i - 1, true
  	}
  	return i, false
  }
docs: // find returns the index where the given item should be inserted into this
  // list.  'found' is true if the item already exists in the list at the given
  // index.