private function extractField($blocks)
    {
        $fieldData = array();

        $pattern = "/([a-zA-Z]+) *(.+)/";

        foreach ($blocks as $block) {
            $match = preg_match($pattern, $block, $matches);

            // A full double string match found
            if (count($matches) == 3) {
                $docLabel = trim(strtolower($matches[1]));
                $docValue = trim($matches[2]);

                if (in_array($docLabel, self::$VALID_EXPRESSIONS)) {
                    $fieldData[self::$VALID_EXPRESSIONS_NAMES[$docLabel]] = $docValue;
                }
            }
        }

        return $fieldData;
    }