To implement a custom input formatter in Flutter, create a class that extends ________.

To implement a custom input formatter in Flutter, create a class that extends TextInputFormatter. This class allows you to define custom formatting logic for text input in text fields. By extending TextInputFormatter, you can intercept and modify user input as it is entered, enabling you to implement custom formatting rules such as masking, character restrictions, or any other desired behavior for input fields in your Flutter applications.