title: jQuery Validate: Validating multiple forms on single page if has same value
body: <p>Example if I have multiple forms, how I can validate the "identity_passport" must be different cannot be the same:</p>
  
  <pre><code>&lt;form id="form_1"&gt;
    &lt;input name="name_1"&gt;
    &lt;input name="email_1"&gt;
    &lt;input name="identity_passport_1" data-field="identity_passport"&gt;
  &lt;/form&gt;
  
  &lt;form id="form_2"&gt;
    &lt;input name="name_2"&gt;
    &lt;input name="email_2"&gt;
    &lt;input name="identity_passport_2" data-field="identity_passport"&gt;
  &lt;/form&gt;
  
  &lt;form id="form_3"&gt;
    &lt;input name="name_3"&gt;
    &lt;input name="email_3"&gt;
    &lt;input name="identity_passport_3" data-field="identity_passport"&gt;
  &lt;/form&gt;
  
  &lt;button type="submit" id="button_submit"&gt;Submit&lt;/button&gt;
  </code></pre>
  
  <p>I have custom submit button that place outside of the form in a single page. I am using .each() method like (below):</p>
  
  <pre><code>&lt;script&gt;
    $('form').each(function () {
  
      $(this).validate({
        errorElement: "span",
        errorPlacement: function (error, element) {
          //
        },
        success: function (label, element) {
          //
        },
        highlight: function (element, errorClass, validClass) {
          //
        }
      });
  
    });
  &lt;/script&gt;
  </code></pre>
  
  <p><strong>UPDATE 2018/01/25:</strong>
  After a long try, is possible. Here is my test and demo:
  <a href="https://jsfiddle.net/claudchan/4t41kjLr/4/" rel="nofollow noreferrer">https://jsfiddle.net/claudchan/4t41kjLr/4/</a></p>