repeated_ptr_field.h -- document lifetime of pointers and references

In STL containers that store value elements (e.g. vector<Bar> as opposed to vector<Bar*>), element pointers are invalidated by operations such as adding or removing elements from the container.

The generated C++ code for repeated message fields returns a container of value elements:
https://protobuf.dev/reference/cpp/cpp-generated/#repeatedmessage

const RepeatedPtrField<Bar>& bar()
RepeatedPtrField<Bar>* mutable_bar()

However, based on the "Ptr" in the name, and looking at the current implementation, it seems that the intention is for RepeatedPtrField to behave more like vector<Foo*>, where it is safe to hold on to pointers to the underlying messages.

For example, is this safe?:

message Bar {
  string baz = 1;
}
message Foo {
  repeated Bar bar = 1;
}
...

std::string do_something(Foo *foo) {
  // Get a reference to first element of bar
  const Bar& bar = *foo->bar()->begin();

  // Add a bar to foo
  foo->add_bar();

  // Do something with the first bar reference
  return bar.baz();
}

I'm not finding clear documentation on this behavior though. Assuming it is meant to be safe to hold on to these references/pointers, could this please be documented?

Related stack overflow making the same assumption:
https://stackoverflow.com/questions/33219022/do-pointers-to-items-of-a-repeated-gpb-field-stay-valid-if-the-field-is-modified