title: customising wp_nav_menu and adding text before submenu elements
body: <p>I would want to make a very specific menu with wp_nav_menu that only load the main menu elements and the submenu element of a main menu element if it has been selected.</p>
  
  <p>Exemple:</p>
  
  <blockquote>
    <p>Menu1<br />
    &nbsp;&nbsp;+Submenu1<br />
    &nbsp;&nbsp;+Submenu2<br />
    Menu2<br />
    Menu3<br /></p>
  </blockquote>
  
  <p>I don't want to hide the other submenus using CSS.</p>
  
  <p>I also want to add a "+" before each submenu element.</p>
  
  <p>How can I do this using wp_nav_menu function?</p>
  
  <p>Thanks a lot for your help.</p>