By default the validator uses JavaScript alert boxes to display errors to the user. If we want to display errors in a custom, more user friendly way, use " tmt.validator.errorBoxCallback" as callback:
<form action="index.htm" method="post" tmt:validate="true" tmt:callback="tmt.validator.errorBoxCallback">
If you need more flexibility, you can create a custom callback.
Styling and formatting for error box is specified inside an external CSS file. You can tweak and modify it to suit your needs.