Can a TextBox return any information about appended text (directly)?

I'm aware of detecting when new text is added to a TextBox, however I'd like to know if it's possible to get the appended text directly. I'm only asking because in my circumstance, text inside my TextBox is both ahead, and behind where the user input is focused (eliminating the option to sub(-1) for the newest character appended). Anyway, here are some ideas and things I've tried:

Input Objects

I've also tried using other input events such as InputBegan and InputChanged (opposed to just using the Changed), but it doesn't seem to detect any keyboard input with a TextBox.

Text comparator

If there isn't a simple built-in solution of getting appended text directly, I was thinking about creating something that can find the difference between two text messages. For example:

--> Input
-- arg #1 being original text
-- arg #2 being altered text
func("testing 123", "testing-123")

--> Output
> "-"

That way it wouldn't matter where the text is being appended to, it would just return characters that are inconsistent with the previous change. Either way, I'd love to hear other opinions, ideas, and suggestions, or if I'm just overlooking something very blatant. Thanks.