Which of the following options is not a built-in validation in OutSystems?

The correct choice is based on the understanding of what constitutes built-in validations in OutSystems. Mandatory Fields refer to a validation that checks whether a required field has been filled out by the user. This is a common feature in forms to ensure that necessary information is collected before submission.

Data types of input fields represent another built-in validation mechanism that ensures the user inputs data of the correct type, such as integers, dates, or strings. This helps in maintaining data integrity and prevents errors during data processing.

However, the Maximum length of text fields isn't considered a built-in validation in the same context as mandatory fields or data types. While OutSystems provides mechanisms to manage the length of text inputs, it doesn't automatically enforce a maximum length validation unless specifically configured by the developer using local validations. Developers have to implement such validations manually in their logic or UI configurations for different text inputs.

Thus, the reasoning solidifies the view that the maximum length of text fields does not belong to the set of inherent validations provided by the OutSystems platform unlike the other options.