There’s a de facto convention for rendering footnotes in HTML that enables feed readers to give them special treatment, e.g. NetNewsWire and Feedbin display them inline if you select the numbered footnote popup.
Simon Willison, referencing Chris Coyier, both with screenshots:
I found this code in the NetNewsWire source (it’s MIT licensed) which runs against elements matching this CSS selector:
sup > a[href*='#fn'], sup > div > a[href*='#fn']
So any link with an
hrefattribute containing#fnthat is a child of a<sup>(superscript) element.
This Just Works ™️ in Hugo and I’d never wondered why – it’s a feature of Goldmark, Hugo’s default Markdown parser.
(And I was inspired by Simon to start posting ‘Today I learned’ posts – just a tag at this stage, not sure if I’ll make its own category or subdomain.)