title: jQuery validate across multiple fields
body: <p>I have 3 input fields that ask for the number of people, and of them how many are adults and how many are children. I am trying to use jQuery validate plugin to add a custom method where
  children + adults = number of people</p>
  
  <p>This is my validation call</p>
  
  <pre><code>$("#form2").validate({
      errorElement: "span",
          rules: {
          attendees: {
               required: true,
               digits: true
          },              
          adults: {
               required: true,
               digits: true
          },              
          children: {
               required: true,
               digits: true
          }
      },
      messages: {
          attendees: "Enter the number of persons (including yourself)", 
          adults: "Enter number of adults", 
          children: "Enter number of childern"                
      }               
  });
  </code></pre>
  
  <p>I looked at the group feature and <code>.addMethod()</code> method of the validate plugin but it seems that it was crafted only with one element in mind. Any ideas?</p>