src/HTTP/Request2/CookieJar.php
public function domainMatch($requestHost, $cookieDomain)
    {
        if ($requestHost == $cookieDomain) {
            return true;
        }
        // IP address, we require exact match
        if (preg_match('/^(?:\d{1,3}\.){3}\d{1,3}$/', $requestHost)) {
            return false;
        }
        if ('.' != $cookieDomain[0]) {
            $cookieDomain = '.' . $cookieDomain;
        }
        // prevents setting cookies for '.com' and similar domains
        if (!$this->useList && substr_count($cookieDomain, '.') < 2
            || $this->useList && !self::getRegisteredDomain($cookieDomain)
        ) {
            return false;
        }
        return substr('.' . $requestHost, -strlen($cookieDomain)) == $cookieDomain;
    }
public function domainMatch($requestHost, $cookieDomain)
    {
        if ($requestHost == $cookieDomain) {
            return true;
        }
        // IP address, we require exact match
        if (preg_match('/^(?:\d{1,3}\.){3}\d{1,3}$/', $requestHost)) {
            return false;
        }
        if ('.' != $cookieDomain[0]) {
            $cookieDomain = '.' . $cookieDomain;
        }
        // prevents setting cookies for '.com' and similar domains
        if (!$this->useList && substr_count($cookieDomain, '.') < 2
            || $this->useList && !self::getRegisteredDomain($cookieDomain)
        ) {
            return false;
        }
        return substr('.' . $requestHost, -strlen($cookieDomain)) == $cookieDomain;
    }
Checks whether a cookie domain matches a request host.

The method is used by {@link store()} to check for whether a document
at given URL can set a cookie with a given domain attribute and by
{@link getMatching()} to find cookies matching the request URL.

@param string $requestHost  request host
@param string $cookieDomain cookie domain

@return   bool    match success