Source

File: wp-includes/Requests/Cookie.php

public function is_expired() {
		// RFC6265, s. 4.1.2.2:
		// If a cookie has both the Max-Age and the Expires attribute, the Max-
		// Age attribute has precedence and controls the expiration date of the
		// cookie.
		if (isset($this->attributes['max-age'])) {
			$max_age = $this->attributes['max-age'];
			return $max_age < $this->reference_time;
		}

		if (isset($this->attributes['expires'])) {
			$expires = $this->attributes['expires'];
			return $expires < $this->reference_time;
		}

		return false;
	}