<http://schema.org/description>
"At the heels of Google and Yahoo, and Bing's tests, Yandex, the largest Russian search engine has dropped out all search query data from the referrer.  That means, Yandex has gone 100% not provided.  "^^<http://www.w3.org/2001/XMLSchema#string>
<https://www.seroundtable.com/yandex-not-provided-18715.html>