title: Simple datepicker validation
body: <p>Can someone help me write a function for showing a line of text (preferably by showing a css class) for a jquery datepicker after someone has clicked a date?</p>
  
  <p>The notice has to appear IF the date picked falls between TODAY and 21 DAYS FROM TODAY.</p>
  
  <p>It's the function I need help with, as I don't know how to write it.</p>
  
  <pre><code>&lt;script&gt;
       $(function() {
            $( "#delivery_date" ).datepicker({ 
                  dateFormat: "dd/mm/yy",
            });
       });
   &lt;/script&gt;
  
  &lt;input type="text" id="delivery_date" name="delivery_date" required  /&gt;
  </code></pre>