The following code example is taken from the book
C++20 - The Complete Guide by Nicolai M. Josuttis, Leanpub, 2021
The code is licensed under a Creative Commons Attribution 4.0 International License. Creative Commons License

// raw code

#include <iostream>
#include <string>
#include <vector>
#include <array>
#include <ranges>
#include "printcoll.hpp"

int main()
  std::vector<std::string> rg1{"he", "hi", "ho"};
  std::vector<std::string> rg2{"---", "|", "---"};
  std::array coll{rg1, rg2, rg1};

  printColl(coll);                                       // ranges of ranges of strings
  printColl(std::ranges::join_view{coll});               // range of strings
  printColl(coll | std::views::join);                    // range of strings
  printColl(coll | std::views::join | std::views::join); // ranges of chars