make a field required only if it's visible

jQuery.validate.requiredIfVisible.js

// jQuery.validate.requiredIfVisible.js
// Copyright (c) 2010 Ori Peleg, http://orip.org, distributed under the MIT license
(function($) {
$.validator.addMethod(
    "requiredIfVisible",
    function(value, element, params) {
      function isVisible(e) {
        // the element and all of its parents must be :visible
        // inspiration: http://remysharp.com/2008/10/17/jquery-really-visible/
        return e.is(":visible") && e.parents(":not(:visible)").length == 0;
      }

      if (isVisible($(element))) {
        // call the "required" method
        return $.validator.methods.required.call(this, $.trim(element.value), element);
      }

      return true;
    },
    $.validator.messages.required
  );
})(jQuery);

Ultimately worked for me in Chrome after wrapping the 'return true;' line in an else clause:

if (isVisible($(element))) {
return $.validator.methods.requried.call(this, $.trim(element.value), element);
} else {
return true;
}