Recently, the first Google search in a clean, guest or incognito browser window has the parameter sei appended to the URL (e.g. https://www.google.com/search?q=example) with a 22- or 23-digit cryptic value (e.g. FFKeZ7zZJveB9u8P9PCGiQY): https://www.google.com/search?q=example&sei=FFKeZ7zZJveB9u8P9PCGiQY
What is this all about?