Ignore all hidden div but not one in jQuery validation

You can use the :not() selector:

ignore: ":hidden:not(.my_item)"

Accepted answer is perfectly fine but when you need some more control than the jQuery selector provides. You could pass a function that tests each element.

for example:

ignore: function (index, el) {
   var $el = $(el);

   if ($el.hasClass('always-validate')) {
       return false;
   }

   // Default behavior
   return $el.is(':hidden');
},