demo · v135

Hover, focus, long-press → invoke

The interestfor attribute on <button> and <a> declaratively shows a popover (or invokes another command) when the user "shows interest" — hover with a mouse, focus from the keyboard, long-press on touch. No JavaScript wiring needed.

Behind a flag Enable chrome://flags/#html-interestfor to use the real attribute. The demo also wires up a JS fallback so the popover works in any browser.
interestfor: ?

Bertrand Russell wrote that paradox sometimes signals genuine progress in mathematics. Hover the underlined word, focus it with Tab, or long-press it on mobile.

Russell's paradox

Whether the set of all sets that don't contain themselves contains itself. Discovered 1901 — collapsed Frege's naive set theory.

event log

the code

<a href="/glossary/paradox" interestfor="card-1">paradox</a>

<div popover="auto" id="card-1">
  <h4>Russell's paradox</h4>
  <p>…</p>
</div>

see also