from, until, rev_until, rev_from이 뭔가요?

// reverse_iterator example
#include <iostream>     // std::cout
#include <iterator>     // std::reverse_iterator
#include <vector>       // std::vector
 
int main () {
  std::vector<int> myvector;
  for (int i=0; i<10; i++) myvector.push_back(i);
 
  typedef std::vector<int>::iterator iter_type;
                                                         // ? 0 1 2 3 4 5 6 7 8 9 ?
  iter_type from (myvector.begin());                     //   ^
                                                         //         ------>
  iter_type until (myvector.end());                      //                       ^
                                                         //
  std::reverse_iterator<iter_type> rev_until (from);     // ^
                                                         //         <------
  std::reverse_iterator<iter_type> rev_from (until);     //                     ^
 
  std::cout << "myvector:";
  while (rev_from != rev_until)
    std::cout << ' ' << *rev_from++;
  std::cout << '\n';
 
  return 0;
}