title: jQuery reject certain characters input
body: <p>I'm making a system where you press a key and it changes text box. I only want to be able to put the values <code>X, x, E, e, /</code>
  My current jQuery code is </p>
  
  <pre><code>$('.today').keyup(function(e) {
    var self = $(this);
    var currentInput = self.data('number');
    var next = $(currentInput + 1);
    var previous = $(currentInput - 1);
    var keyCode = e.keyCode || e.which;
    var num = self.data('number') + 1;
    var nom = self.data('number') - 1;
    if(('input.today[data-number="' + num +'"]').length &amp;&amp; keyCode === 40)
      $('input.today[data-number="' + num +'"]').focus()
    else if(('input.today[data-number="' + nom +'"]').length &amp;&amp; keyCode === 38)
      $('input.today[data-number="' + nom +'"]').focus();
    else if(('input.today[data-number="' + num +'"]').length &amp;&amp; self.val().length == self.attr('size')) {
      $('input.today[data-number="' + num +'"]').focus();
    }
  });
  </code></pre>
  
  <p>I only want the focused box to move if the key up is one of these: <code>X, x, E, e, /, UP, DOWN, LEFT, RIGHT</code>. And if the values are not <code>X, x, E, e, /</code> then to not write in the box</p>