<Validation Message> is not used to validate input but rather to display a message when input is invalid. If it is not empty the client behaves as follows:
1. The display element will appear with a red background and (when hovering over it) a tooltip containing the text in <Validation Message>.
2. If a button in a same view has html.validate property set to true (the default for new buttons), then when the button is pressed it's modeling is not performed, and instead the <Validation Message> is displayed as an alert.
To validate input, you should add an <On Change> action to each input element you wish to validate, and model the validation (which ultimately results in setting or clearing <Validation Message>) in there.
For best results, use the Firefox browser..