What is the interface behavior when a widget is not valid (Valid set to False)?

When a widget's valid property is set to False, the interface behavior typically involves providing visual feedback to the user to indicate that there is an issue with the input. Choosing this behavior enhances user experience by drawing attention to the error without completely obscuring the widget.

In this case, the correct answer indicates that the regular widget remains visible, which ensures users can see the widget they need to correct. The application of a specific styling, such as a red border, serves as an immediate cue that something is wrong. Additionally, displaying the validation error message when the widget gains focus allows users to clearly understand what the issue is at the moment they attempt to engage with the input field, promoting clarity and ease of correction.

This approach is effective in user interface design, as it keeps users informed and promotes a smoother interaction as they work to resolve input errors. It supports an iterative correction process, where users can directly interact with the widget and receive feedback in a timely manner.