private static function validateSrcAttribute(Header $header, $attributeName)
    {
        Types::assert(['string' => [$attributeName]], [2]);

        $Errors = [];

        if ($header->hasAttribute($attributeName))
        {
            $value = $header->getAttributeValue($attributeName);

            $badFlags = ["'unsafe-inline'", "'unsafe-eval'"];
            foreach ($badFlags as $badFlag)
            {
                if (strpos($value, $badFlag) !== false)
                {
                    $friendlyHeader = $header->getFriendlyName();

                    $Errors[] = new Error(
                        $friendlyHeader . ' contains the <b>'
                        . $badFlag . '</b> keyword in <b>' . $attributeName
                        . '</b>, which prevents CSP protecting
                                against the injection of arbitrary code
                                into the page.',

                        E_USER_WARNING
                    );
                }
            }
        }

        return $Errors;
    }