AUI Form Validation For file uploads with extension

<aui:input type="file" name="field2" >

    <!--
    For use with input type="file"
    Only allow file uploads with this extension.
    Specify multiple values either comma delimted 'jpg, png',
    whitespace delimited 'jpg png', or pipe 'jpg|png' delimited.
    Do not include the period before the extension
    -->
    <aui:validator name="acceptFiles">
        'jpg, png'
    </aui:validator>
   
</aui:input>