no-nonstandard-features

Warns about elements and attributes marked as non-standard in the HTML specification data bundled with markuplint.

info

Split from the former no-unsupported-features rule's checkNonStandard option (#3989). Enabling this rule is equivalent to the old checkNonStandard: true. See the no-unsupported-browser-features rule for the browserslist-based support check, or the no-experimental-features rule for experimental features.

Default Severity

warning

Options

Option	Type	Default	Description
ignoreFeatures	string[]	[]	Features to ignore.

ignoreFeatures Format

Uses exact string matching (no glob or wildcard patterns), except for the case of letters. The element part is compared as the tag names of the language are: case-sensitively where the parser tells the case of a tag name apart (JSX, Svelte, Astro, MDX), and without regard to ASCII case otherwise. The attribute part is compared as the DOM compares the name of that attribute (see Attribute name case).

• "dialog" — Ignores the <dialog> element. The element name is compared as the document compares tag names: without regard to ASCII case in HTML, and exactly in a syntax that tells tag names apart (JSX, Svelte), where DIALOG is not <dialog>.
• "input[list]" — Ignores the list attribute on <input> elements. The attribute name is compared as the DOM compares it with the attribute that is checked: LIST is the same attribute in HTML, and on an HTML element in JSX or Svelte, but on an <svg> element that JSX sets, only the same spelling is.

Examples

❌ Examples of incorrect code for this rule

<canvas moz-opaque></canvas>

✅ Examples of correct code for this rule

<canvas></canvas>

Migration from deprecated-element

In v4.x, the deprecated-element rule detected deprecated, obsolete, and non-standard elements. In v5.x, the non-standard detection has moved to this rule.

{
  "rules": {
    "no-nonstandard-features": true
  }
}

If you use the recommended preset, this is already enabled automatically via the compat preset.

Interface

{
  "no-nonstandard-features": boolean
}

Options

{
  "no-nonstandard-features": {
    "options": {
      "ignoreFeatures"?: string[]
    }
  }
}

Property	Type	Default Value	Description
ignoreFeatures	string[]	undefined	Features to ignore. Element name ("dialog") or attribute pattern ("input[list]").

Default Severity

warning