Why Use This Pattern
Form Validation provides specific contextual instructions on how to solve the problem. The validation message is presented next to a control or section of a form that has a problem as in the case incorrect or malformed data. It verifies that a form has all required information and that it is in the correct format. It validates user input at the field level, at the page level, and when the user submits a dialog or wizard
What is the Solution
Provide field-level validation so that users get immediate feedback when a problem is found, while focus is in a text input box, or immediately after it loses focus. A text box with invalid data has a red border. When the user moves the pointer over the text box, a red tooltip (contectual message) appears.
Form validation used to occur at the server, after the user had entered all necessary data and then pressed the 'Submit' button. If some of the data that had been entered by the user was in the wrong form or was simply missing, the system would have to send all the data back to the user, and request that the form be resubmitted with correct information.