Lithium: How to add html attributes after form validation

Question

I'm using form helper and Validator Util. After form submission a div with error class appended to the fields were not verified.

How we can add html attributes to this fields too?

generated sample which errorClass added because of field error:

<div class="form-group">
    <label for="fieldName">Label text</label>
    <input type="text" name="fieldName" class="errorClass" max-length="15" id="fieldName">
    <div class="error">Error description.</div>
</div>