Determines validity by running through an array of functions in the data object.

jquery.validate.js

// Checks if a DOM object is valid.
// Expects an array of functions in data('validations') that return true when
// valid.
//
// Triggers field_invalid or field_valid.
// Calls options.invalid() or options.valid().

$.fn.validate = function(options) {
  var $this = $(this);
  /* $this.data('validations') is an array of functions, each of which
   * accepts the value of the form field, and returns true if it passes the
   * validation, and false if it fails.
   */
  if($this.data('validations')) {
    var invalid = false;
    $.each($this.data('validations'), function() {
      if(!this($this.val())) {
        invalid = true;
        return false;
      }
    });
    if(invalid) {
      $this.trigger('field_invalid');
      $this.focus().select();
      if(options && options.invalid) options.invalid();
    } else {
      $this.trigger('field_valid');
      if(options && options.valid) options.valid();
    }
  }
};