Thanks for the links.
They explain how to create and use shortcodes but not how to document a specific shortcode.
In the example I gave, I needed to remember the name of the plugin (create_link_to_supplier), and the name of the attributes (id, tag, user).
I’d hoped that there would be some standard way of doing shortcode documentation – as there is with a plugin – but couldn’t find it. Maybe that’s just the way it is ??