public function validate(FormField $field)
 {
     $value = strlen($field->get_value());
     $is_required = $field->is_required();
     if (!empty($value) || $is_required) {
         return $value >= $this->lower_bound && $value <= $this->upper_bound;
     }
     return true;
 }
 public function validate(FormField $field)
 {
     $value = $field->get_value();
     $is_required = $field->is_required();
     if ($value instanceof Date) {
         $value = $value->format(Date::FORMAT_ISO_DAY_MONTH_YEAR);
     }
     if (!empty($value) || $is_required) {
         return preg_match($this->php_regex, $value) > 0;
     }
     return true;
 }
 public function validate(FormField $field)
 {
     $is_required = $field->is_required();
     $value = $field->get_value();
     if (!is_numeric($value)) {
         return false;
     }
     $value = (int) $value;
     if (!empty($value) || $is_required) {
         return $value <= $this->upper_bound;
     }
     return true;
 }