title: Gravity Forms - Validate first 6 characters of a field is equal to date field before submission
body: <p>I've two fields which are :-</p>
  
  <ol>
  <li>Date field (dd/mm/yyyy) [Field ID 5]</li>
  <li>Text field (mask format is 999999-99-9999) [Field ID 6]</li>
  </ol>
  
  <p>I want to verify that the first 6 characters of the Text field is equal to the Date field in yymmdd format. Which means, if the date selected is 15/02/2001, the text field input should be 010215-XX-XXXX (X can be any characters). </p>
  
  <p>I already checked the Gravity Forms documentation, but I've no idea how to grab the input field value and also how to convert the date field value to yymmdd and how to grab only the first 6 characters of the text field value. This is what I got so far :-</p>
  
  <pre><code>$birthDateInput = 'To get field_id_5 &amp; convert it into yymmdd';
  $icInput = 'To get field_id_6 &amp; only grab the first 6 characters';
  
  function gravityICFormValidation( $result, $value, $form, $field )
  {
  
      if( $icInput != $birthDateInput )
          {
              $result['is_valid'] = false;
              $result['message'] = 'Your IC Number "'.$icInput.'" is different than your Date of Birth.';
          } 
  
      return $result;
  }
  add_filter( 'gform_field_validation_1_6', 'gravityICFormValidation', 10, 4 );
  </code></pre>