a11y/deprecated-element · Obsolete HTML element

An element in the HTML standard's obsolete-features list is non-conforming and has a conforming replacement.

Severity: info · Category: a11y

Scored info rather than warning: the element still renders and browsers keep it working. What is lost is the guarantee: its semantics are unspecified for assistive technology, and each element has a replacement the standard does define.

What it checks

Flags an element named in the HTML standard’s obsolete-features list, meaning <center>, , <strike>, <big>, <tt>, <frame>, <applet> and the rest of that section, in component source.

Not flagged:

Anything inside <svg>, or in a component declaring <svelte:options namespace="svg" />. The check is for HTML elements only; content under <foreignObject> returns to HTML and is checked.
The conforming replacements: <s> for <strike>,  plus CSS font-size for <big> (/ would change the meaning), <code>/<kbd>/<samp> for <tt>.

<strike>old price</strike>
<font color="red">styled with markup</font>

<marquee> and <blink> are reported here and by the Svelte compiler (a11y_distracting_elements). That overlap is deliberate: the compiler streams into the build log and does not score, gate, or suppress, and a score that counted  but not <marquee> would be blind to two obsolete elements. The two never disagree; both say the element must go.

An obsolete element yields one finding. Its deprecated attributes () are not reported a second time by a11y/deprecated-attr, and that stays true when this rule is turned off or suppressed inline: the attribute rule skips obsolete elements by name, not by looking at this rule’s result.

The element list is the obsolete column of the vendored HTML spec data (@markuplint/html-spec), which matches the WHATWG obsolete-features section exactly.

Why it matters

Obsolete elements are non-conforming: browsers keep rendering them so that legacy pages do not break, but the standard defines no meaning for them, so what assistive technology announces, and what a future browser renders, is not something the page can rely on. Each has a replacement whose semantics are defined.

How to fix

Replace the element with its conforming equivalent and move presentation to CSS:

<s>old price</s>
<span class="alert">styled with CSS</span>

Mode differences

None. This rule reads source, the same .svelte and .ts files, everywhere it runs. The CLI, the Vite plugin’s build pass, and the live dashboard’s static baseline all report it identically, and the rendered-HTML pass never re-evaluates it. Scoping a run with --route skips it: component-scoped rules have no route to attribute a finding to.

Disabling

Silence a single element with , or turn the rule off:

export default {
  rules: {
    'a11y/deprecated-element': 'off'
  }
};