public function isValid(Field $field) { return filter_var($field->getValue(), FILTER_VALIDATE_EMAIL) !== false; }
public function isValid(Field $field) { return is_numeric($field->getValue()); }
public function isValid(Field $field) { return !empty($field->getValue()); }
public function isValid(Field $field) { return call_user_func($this->callable, $field->getValue()); }
public function isValid(Field $field) { return strlen($field->getValue()) <= $this->max; }
public function isValid(Field $field) { return preg_match($this->pattern, $field->getValue()); }
public function isValid(Field $field) { return ctype_alpha($field->getValue()); }