What you can do is attach an onsubmit event to your form.
This means that when the user submits their data, a function is fired which validates the user's input.
If the input meets the appropriate criteria, the function returns true and the form is submitted.
Otherwise the function, displays an error message and returns false. This will stop submission.
If this is the kind of thing your after, it's not hard to code, so just let me know.