The standard needs to better clarify the section on vector iterator invalidation.

Why i think its important:

Some implementations added checks like: "oh, we must store all .end() iterators into global map under mutex and mark them invalid on each push_back, it will be SO useful for our developers!"
So, minimal example where it breaks completely:

 std::vector<int> v;
  v.reserve(10);

  v.push_back(1);

  auto b = v.begin();
  auto e = v.end();
  v.push_back(1);
  ++b;
  REQUIRE(b == e); // assertion failure:
  // _STL_VERIFY(this->_Getcont() == _Right._Getcont(), "vector iterators incompatible");

Its common pattern when using vector to reserve memory and push values, there are no "better way to do it", thats why it must be valid


Now about standard:

here's a quote from the standard regarding append_range and, apparently, push_back (https://eel.is/c++draft/vector#modifiers-2):

  

It explicitly states that despite there are no relocation happen, the past-the-end iterator is invalidated, although there's no reason for a vector to be so.
Yes, a past-the-end iterator will no longer be past-the-end, but that doesn't make it invalid. In any implementation, even a foolish one, it's hard to imagine how, without relocation, this iterator could become anything other than just an iterator to the last element of the vector.