a11y/pattern-title · Pattern input without a format description

When an input has a pattern, the spec says authors should include a title describing the expected format; without it a failed submit tells the user only that the value is wrong.

Severity: info · Category: a11y

What it checks

Flags an <input> with a literal pattern but no title describing the expected format:

<input pattern="[A-Za-z]+-[0-9]+" />

Only inputs where pattern is actually effective are judged: no type (the missing type defaults to Text) or a literal type in the spec’s applies-to set: text, search, url, tel, email, password (matched case-insensitively). A blank literal title="" describes nothing and is flagged; an expression-valued title={expr} counts as present.

Not flagged:

A literal type outside the applies-to set (type="number"), where pattern is inert, so requiring a title would be wrong.
An expression-valued type or pattern, which is unknowable statically.
An input with a spread attribute, or one inside <svg> (it never renders as a form control there).

Why it matters

The spec says that when a pattern attribute is specified, authors should include a title giving a description of the pattern. Browsers surface that title in the validation error, so without it a failed submit tells the user only that the value is wrong, not what right looks like.

How to fix

Describe the expected format in plain words, and mirror it in visible help text (title alone is unavailable to touch and keyboard users and to many assistive-technology users):

<input pattern="[A-Za-z]+-[0-9]+" title="Letters, a dash, then digits" />

Limitations

An unknown type keyword (type="txet") falls back to the Text state per spec, where pattern does apply, but this rule skips types outside the known set rather than guess at typos, a deliberate, conservative false negative.

A regex quantifier brace ({3}) is parsed as a Svelte expression inside a template attribute, so a pattern using one is typically written as an expression, pattern={'[A-Za-z]{3}[0-9]{4}'}, which this rule skips as unknowable. Patterns written as plain literals (no braces) are fully covered.

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

If the format is explained some other way this rule can’t see (visible help text tied via aria-describedby), silence the element with , or turn the rule off:

export default {
  rules: {
    'a11y/pattern-title': 'off'
  }
};