protected function getVatRateLookupMetadataByTaxClass($taxClassId)
    {
        // '' denotes the 'standard'tax class, use 'standard' in meta data, ''
        // when searching.
        if ($taxClassId === '') {
            $taxClassId = 'standard';
        }
        $result = array(
            Meta::VatClassId => sanitize_title($taxClassId),
            // Vat class name is the non-sanitized version of the id
            // and thus does not convey more information: don't add.
            Meta::VatRateLookup => array(),
            Meta::VatRateLookupLabel => array(),
        );
        if ($taxClassId === 'standard') {
            $taxClassId = '';
        }

        // Find applicable vat rates. We use WC_Tax::find_rates() to find them.
        $args = array(
            'tax_class' => $taxClassId,
            'country' => $this->invoice[Tag::Customer][Tag::CountryCode],
            'city' => isset($this->invoice[Tag::Customer][Tag::City]) ? $this->invoice[Tag::Customer][Tag::City] : '',
            'postcode' => isset($this->invoice[Tag::Customer][Tag::PostalCode]) ? $this->invoice[Tag::Customer][Tag::PostalCode] : '',
        );
        $taxRates = WC_Tax::find_rates($args);
        foreach ($taxRates as $taxRate) {
            $result[Meta::VatRateLookup][] = $taxRate['rate'];
            $result[Meta::VatRateLookupLabel][] = $taxRate['label'];
        }
        return $result;
    }