WCAG 3.1.3 — Unusual Words

What this requires

A mechanism is available for identifying specific definitions of words or phrases used in an unusual or restricted way, including idioms and jargon. The mechanism can be inline (a definition list on the page, a <dfn> element on first use), contextual (a tooltip or popover), or external (a glossary linked from the page).

How AI coding tools fail this

When asked to write technical documentation or marketing copy, AI tools use industry shorthand without defining it. "Serverless", "observability", "shift-left", "developer experience" — terms that mean very specific things inside the niche and roughly nothing outside it.

The second pattern: glossaries that exist as a separate page but aren't linked from where the terms appear. The reader has to know the glossary exists, leave the article, search for the term, and return.

The third: definitions hidden behind hover tooltips with no discoverable affordance. A keyboard or touch user has no way to find them.

Passing examples

Define on first use with <dfn> and a glossary link:

<p>
  Our platform supports{" "}
  <dfn>
    <a href="/glossary#observability">observability</a>
  </dfn>{" "}
  — the ability to understand what is happening inside a system based
  on its outputs — across the entire request lifecycle.
</p>

A definition popover keyed off a button (not hover):

<p>
  We instrument every request with{" "}
  <Popover>
    <Popover.Trigger asChild>
      <button className="border-b border-dotted text-link">
        traces
      </button>
    </Popover.Trigger>
    <Popover.Content>
      A trace is a record of the path a request takes through the
      system, including timing for each step.
    </Popover.Content>
  </Popover>{" "}
  and report them to the observability backend.
</p>

Edge cases

Audience expectation matters. A technical-architecture document on a tools site can use "API" without definition; a marketing landing page might not.
Linked glossary entries are the cheapest mechanism on a docs site. Build it once, reuse everywhere.
<dfn> element marks the defining instance of a term, helping screen readers and indexes.
Idioms ("by and large", "out of pocket") are also in scope. A multilingual audience may not parse them.
AAA target. Most projects target AA; 3.1.3 is the polish layer.

How Jeikin handles this

This is a manual editorial review. The dashboard records, per content piece, whether a glossary is linked and whether jargon is defined on first use. The scanner can extract candidate jargon terms from a lexicon and surface them for review, but the call is editorial.

References

W3C — Understanding 3.1.3 Unusual Words (opens in new tab)