Zend\Diactoros\RequestTrait::validateMethod PHP Method

    private function validateMethod($method)
    {
        if (null === $method) {
            return;
        }
        if (!is_string($method)) {
            throw new InvalidArgumentException(sprintf('Unsupported HTTP method; must be a string, received %s', is_object($method) ? get_class($method) : gettype($method)));
        }
        if (!preg_match('/^[!#$%&\'*+.^_`\\|~0-9a-z-]+$/i', $method)) {
            throw new InvalidArgumentException(sprintf('Unsupported HTTP method "%s" provided', $method));
        }
    }