The following code example is taken from the book
C++ Move Semantics - The Complete Guide by Nicolai M. Josuttis, Leanpub, 2020
The code is licensed under a Creative Commons Attribution 4.0 International License. Creative Commons License

// raw code

#include <iostream>
#include <string>
#include <vector>

template<typename T>
class Coll {
  std::vector<T> values;
  Coll() = default;

  // function in class template:
  void insert(T&& val) {

int main()
  Coll<std::string> coll;
  coll.insert(std::string{"prvalue"});  // OK
  std::string str{"lvalue"};
  coll.insert(str);              // ERROR: T&& of Coll is not a universal reference
  coll.insert(std::move(str));   // OK