A OneBox converts your web links into useful preview excerpts that help inform readers about the target before they click through.
So if a user on another site wanted to show the OneBox for https://swi-prolog.discourse.group they would put the link on a line by itself, e.g.
Test to demonstrate a OneBox.
https://swi-prolog.discourse.group/
This is a test of a one box for SWI-Prolog
and it currently shows up as
Many sites have a nice sentence that describes the site in the OneBox.
While we know what SWI-Prolog is, our OneBox should also state that.
The text for the OneBox is from the HTML meta field with name="description" and uses content="SWI-Prolog forum" for the wording.
<html lang="en-US" class="desktop-view not-mobile-device text-size-normal">
<head>
<meta charset="utf-8">
<title>SWI-Prolog - Users and developers of SWI-Prolog, an implementation of the Prolog programming language</title>
<meta name="description" content="SWI-Prolog forum">
The Discourse setting for the content value can be found with
Admin → Settings → Required → site description
Should we change it to
SWI-Prolog offers a comprehensive free Prolog environment. Since its start in 1987, SWI-Prolog development has been driven by the needs of real world applications. SWI-Prolog is widely used in research and education as well as commercial applications.
Or something with one less sentence as that will probably get cut off.
NB I don’t know how to get a OneBox for this site on this site. To get the OneBox image above I had to use another site.