1. Create a text frame with 2 Anchored text frames with the same width.
2. Make the anchored frames Auto-Size --> Vertical only
3. insert text to the first frame, when type enter to the next line the frame become higher but the next frame remain in the same position. just after typing the first character in the second line the next frame adjust in the right position.
4. The same happen when pasting text that make the frame bigger.
5. The same happen without Auto-Size when fit frame to content.