The about and mentions markups are properties of webpage schema which explicitly tell search engines like Google and Bing what topics a page is primarily about and what other subjects are just getting outlined or referred to. It features references for the Schema.org and Google documentation for the particular form https://bookmarkforce.com/story19507846/helping-the-others-realize-the-advantages-of-seo-automatique-google-rich-snippets-json-ld-open-graph