1. Form validation

    Method of setting required fields and field types without requiring JavaScript. This includes preventing forms from being submitted when appropriate, the `checkValidity()` method as well as support for the `:invalid`, `:valid`, and `:required` CSS pseudo-classes.

  2. elementinternals api: ariainvalid

  3. element api: ariainvalid

  4. htmlinputelement api: `invalid` event

  5. webgl2renderingcontext api: invalidateframebuffer

  6. webgl2renderingcontext api: invalidatesubframebuffer

  7. xpathresult api: invaliditeratorstate

  8. css at-rule: `@font-face`: src: drop invalid item (not src string)

  9. css selector: `:-moz-submit-invalid`

  10. css selector: `:invalid`

  11. css selector: `:invalid`: applies to `<form>` elements

  12. css selector: `:user-invalid`