How is the output of the page content (title, photos and parts of the text) arranged by a link in VKontakte or Facebook posts?

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I just can’t find how to display a fragment of another page in a text editor (and then in a post) on my site when you enter a link to it. That is, when a person wants to publish a link to some page and immediately after entering the link, he sees a fragment of this page in his editor and then in a published post, as is done in VK, FB and other social networks. networks?
Is it a kind of parsing or how does it work?