<required>true</required>

<config>
   <sections>
    <au translate="label" module="auth">
        <groups>
            <aug translate="label" module="auth">
                <fields>
                    <email_input translate="label">
                        <required>true</required>
                        <label>email: </label>
                        <frontend_type>text</frontend_type>
                        <sort_order>1</sort_order>
                    </email_input>
                </fields>
            </aug>
        </groups>
    </au>
</sections>

<field id="au" translate="label" required="true"type="text" sortOrder="1" showInDefault="1" showInWebsite="0" showInStore="1">
    <label>email:</label>
 </field>

<field id="au" translate="label" type="text" sortOrder="1" showInDefault="1" showInWebsite="0" showInStore="1">
    <label>email:</label>
    <required>true</required>
</field>

<field id="title" translate="label" type="text" sortOrder="5" showInDefault="1" showInWebsite="1" showInStore="1">
                    <label>Title</label>
                   <validate>required-entry</validate>
   </field>

<field id="title" translate="label" type="text" sortOrder="5" showInDefault="1" showInWebsite="1" showInStore="1">
                    <label>Title</label>
                    <validate>required-entry validate-digits</validate>
   </field>

'required-entry'                => 'This is a required field.'
'validate-number'               => 'Please enter a valid number in this field.'
'validate-email'                => 'Please enter a valid email address. For example
johndoe@domain.com.'
'validate-date'                 => 'Please enter a valid date.'
'validate-select'               => 'Please select an option.'
'validate-no-html-tags'         => 'HTML tags are not allowed'
'validate-digits'               => 'Please use numbers only in this field. Please avoid spaces or other characters such as dots or commas.'
'validate-url'                  => 'Please enter a valid URL. Protocol is required (http://, https:// or ftp://)'
'validate-not-negative-number'  => 'Please enter a number 0 or greater in this field.'
'validate-zero-or-greater'      => 'Please enter a number 0 or greater in this field.'
'validate-state'                => 'Please select State/Province.'
'validate-cc-number'            => 'Please enter a valid credit card number.'
'validate-data'                 => 'Please use only letters (a-z or A-Z), numbers (0-9) or underscore(_) in this field, first character should be a letter.'

<field id="au" translate="label" type="text" sortOrder="1" showInDefault="1" showInWebsite="0" showInStore="1">
    <label>email:</label>
    <validate>required-entry</validate>
</field>

'validate-no-html-tags' => 'HTML tags are not allowed'
'validate-select' => 'Please select an option.'
'required-entry' => 'This is a required field.'
'validate-number' => 'Please enter a valid number in this field.'
'validate-digits' => 'Please use numbers only in this field. Please avoid spaces or other characters such as dots or commas.'
'validate-date' => 'Please enter a valid date.'
'validate-email' => 'Please enter a valid email address. For example johndoe@domain.com.'
'validate-url' => 'Please enter a valid URL. Protocol is required (http://, https:// or ftp://)'
'validate-not-negative-number' => 'Please enter a number 0 or greater in this field.'
'validate-zero-or-greater' => 'Please enter a number 0 or greater in this field.'
'validate-state'  => 'Please select State/Province.'
'validate-cc-number' => 'Please enter a valid credit card number.'
'validate-data' => 'Please use only letters (a-z or A-Z), numbers (0-9) or underscore(_) in this field, first character should be a letter.'