Source

File: wp-includes/Requests/IRI.php

protected function set_port($port) {
		if ($port === null) {
			$this->port = null;
			return true;
		}

		if (strspn($port, '0123456789') === strlen($port)) {
			$this->port = (int) $port;
			$this->scheme_normalization();
			return true;
		}

		$this->port = null;
		return false;
	}