title: jQuery validation of multiple not equal inputs
body: <p>I've managed to set up jQuery validate plugin on my form and I gave rules for two fields in which their values should not match. Specifically, the email and email_2 inputs can not be the same now, and that works. But my real need is to validate multiple inputs in the same way (in this case 4 of them). I have email, email_2, email_3, email_4 and none of them should not be equal. You can see it in my <a href="http://jsfiddle.net/zPetY/" rel="noreferrer">jsfiddle here</a>, and if you have solution, you can update it and put it back in answer: </p>
  
  <p>html:</p>
  
  <pre><code>&lt;form id="signupform" method="post"&gt;
  &lt;input id="email" name="username" /&gt;
  &lt;br/ &gt;
  &lt;input id="email_2" name="email_2" /&gt;
  &lt;br /&gt;
  &lt;input id="email_3" name="email_3" /&gt;
  &lt;br /&gt;
  &lt;input id="email_4" name="email_4" /&gt;
  &lt;br /&gt;
  &lt;input id="submit" type="submit" value="submit" /&gt;   
  &lt;/form&gt;
  </code></pre>
  
  <p>jquery:</p>
  
  <pre><code>$.validator.addMethod("notequal", function(value, element) {
   return $('#email').val() != $('#email_2').val()}, 
   "* You've entered this one already");
  
  // validate form    
  $("#signupform").validate({
  
  rules: {
      email: {
          required: true,
          notequal: true
      },
      email_2: {
          required: true,
          notequal: true
      },
  },
  });
  </code></pre>
  
  <p>what is the best solution for validate of all inputs?</p>