And the jQuery is just that simple!

$(document).ready(function(){
     $("legend").click(function(event){
          if ( $(this).parent().children('div').is('.hidden') ) {
              $(this).parent().children('div').removeClass('hidden') ;
              }
          else {
              $(this).parent().children('div').addClass('hidden') ;
              }
          });
      });

Except I think I will want an external link, so I'll have to add another level of parent(). But jQuery is hardly distinguishable from magic.