What type of validation does not exist in OutSystems?

Input sanitization is not a distinct type of validation in OutSystems. Instead, it is considered part of the broader process of ensuring that the data being processed is safe and appropriate for the application's context. In the OutSystems development environment, while developers implement security measures to sanitize inputs against potential vulnerabilities, this is typically not categorized as a specific type of validation like the other options.

Client-side validation refers to checks that are performed in the user's browser before the data is sent to the server, ensuring a quicker response and a better user experience. Required fields ensure that users enter necessary information before form submission, while maximum length validation limits the character count for text input fields to prevent overflow and maintain the integrity of the database. Each of these plays a clear and significant role in maintaining the application's functionality and user experience, which is why they are well-defined and established within the OutSystems platform.