Why is this Flutter FilteringTextInputFormatter regex not working?

Question

On a Flutter TextField I have the following FilteringTextInputFormatter:

FilteringTextInputFormatter.allow(RegExp(r"^\d+\.?\d{1,2}"));

It tries to match a decimal number up to two places, but I can't input any numbers into the TextField.

https://regexr.com/7fpho

Answer 1

After messing with RegExr, I found that what I wanted was:

RegExp(r"^\d{1,4}(\.\d{0,2})?")

This expression allows four digits with two decimal places.