title: CakePHP 3 - Create multiselect dropdown list
body: <p>Using CakePHP 3 framework. </p>
  
  <p>First of all, I don't know if this is possible. </p>
  
  <p><strong>What I have now</strong></p>
  
  <ul>
  <li>Multiselect checkbox list. </li>
  </ul>
  
  <p><strong>Example</strong></p>
  
  <ul>
  <li>Bikes 1 <em>checkbox</em></li>
  <li>Bikes 2 <em>checkbox</em></li>
  <li>Bikes 3 <em>checkbox</em></li>
  <li>Cars 1 <em>checkbox</em></li>
  <li>Cars 2 <em>checkbox</em></li>
  </ul>
  
  <p>The user is now allowed to select al 5 items. </p>
  
  <p><strong>TODO</strong></p>
  
  <ul>
  <li>Users many-many relation with Vehicles</li>
  <li>Users is allowed to select one per group. </li>
  </ul>
  
  <p><strong>Example TODO (my idea)</strong></p>
  
  <ul>
  <li><p>Dropdown bikes [
  Bikes 1, Bikes 2, Bikes 3
  ]</p></li>
  <li><p>Dropdown cars [ Cars 1, Cars 2 ]</p></li>
  </ul>
  
  <p>The user needs to be only allowed to choose one per group. </p>
  
  <p>Is it possible to achieve this by one array?</p>
  
  <p><strong>EDIT</strong></p>
  
  <p>Is it possible to group a list, like the example above, of radiobuttons?</p>