title: Wordpress TinyMCE add a description to a popup form
body: <p>I have been creating custom buttons for the TinyMCE editor in wordpress today, they are linked to shortcodes and when clicked they open a popup where the user can fill out the parameters for the given shortcode. This all works fine, however I feel it needs a bit more guidance for the users, so I'd like to add a description in the pop-up window under each parameter.</p>
  
  <p>Here is an example of the javascript that handles the popup - you'll see this creates a dropdown list of 5 items for the user to choose from.</p>
  
  <pre><code>(function() {
  tinymce.PluginManager.add('skizzar_container', function( editor, url ) {
      editor.addButton( 'skizzar_container', {
          title: 'Add a Container',
          icon: 'icon dashicons-media-text',
          onclick: function() {
  editor.windowManager.open( {
      title: 'Container',
      body: [{
          type: 'listbox',
          name: 'style',
          label: 'Style',
          'values': [
              {text: 'Clear', value: 'clear'},
              {text: 'White', value: 'white'},                
              {text: 'Colour 1', value: 'colour1'},
              {text: 'Colour 2', value: 'colour2'},
              {text: 'Colour 3', value: 'colour3'},
          ]
      }],
      onsubmit: function( e ) {
          editor.insertContent( '[container style="' + e.data.style + '"]&lt;br /&gt;&lt;br /&gt;[/container]');
      }
  });
  }
  
      });
  });
  })();
  </code></pre>
  
  <p>What I want to do is add some description text underneath the dropdown - how can I achieve this?</p>