How do you inform users that they have entered an invalid value in a field?

Using validation expressions is the most effective way to inform users that they have entered an invalid value in a field. Validation expressions are built directly into the application's logic and allow for real-time feedback when users input data. This feedback can be displayed inline, near the specific field in which the error occurred, providing a clear and immediate indication of any issues.

Validation expressions help ensure data integrity by enforcing rules such as data types, required fields, and specific formatting. By employing this method, users can correct their inputs right away, enhancing their experience and reducing frustration. Immediate feedback through validation promotes a smooth workflow, as users can address issues before attempting to submit the form.

While pop-up messages, status bar warnings, or disabling the submit button could be used to indicate an invalid entry, these methods may not provide the same level of clarity or convenience. Validation expressions directly tied to a field allow users to understand what they need to change, which increases the likelihood of successful data entry on the first attempt.