title: What does this.optional(element) do when adding a jQuery validation method?
body: <p>Please see the documentation:<br>
  <a href="https://jqueryvalidation.org/jQuery.validator.addMethod/" rel="noreferrer">https://jqueryvalidation.org/jQuery.validator.addMethod/</a>  </p>
  
  <p>I wonder what <code>this.optional(element)</code> does. I created two forms to test:<br>
  <a href="https://jsfiddle.net/Mori/ctLqyzhc/" rel="noreferrer">Form1</a> and <a href="https://jsfiddle.net/Mori/Lu0nsaub/" rel="noreferrer">Form2</a> — one with <code>this.optional(element)</code> and the other without it. Theoretically speaking and according to a couple of comments on <a href="https://stackoverflow.com/a/12756090/478018">this answer</a> by Andrew Whitaker: </p>
  
  <blockquote>
    <p>all <code>this.optional</code> does is say "if the field is optional, return true if it is blank"</p>
  </blockquote>
  
  <p>and  </p>
  
  <blockquote>
    <p>The <code>this.optional</code> check is basically checking to see if the field is blank or not before evaluating whether or not it meets the rule.</p>
  </blockquote>
  
  <p>But in action I see no difference in how <a href="https://jsfiddle.net/Mori/ctLqyzhc/" rel="noreferrer">Form1</a> and <a href="https://jsfiddle.net/Mori/Lu0nsaub/" rel="noreferrer">Form2</a> work. Please help me understand the difference in action.</p>