1. :optional CSS pseudo-class

    The `:optional` pseudo-class matches form inputs (`<input>`, `<textarea>`, `<select>`) which are not `:required`.

  2. 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.

  3. batterymanager api: secure context required

  4. beforeunloadevent api: user interaction required for dialog box

  5. cachestorage api: secure context required

  6. caches api: secure context required

  7. crypto api: subtle: secure context required

  8. elementinternals api: ariarequired

  9. element api: ariarequired

  10. eyedropper api: secure context required

  11. gamepadbutton api: secure context required

  12. gamepadevent api: secure context required

  13. gamepadhapticactuator api: secure context required

  14. gamepadpose api: secure context required

  15. gamepad api: secure context required

  16. geolocationcoordinates api: secure context required

  17. geolocationpositionerror api: secure context required

  18. geolocationposition api: secure context required

  19. geolocation api: secure context required

  20. htmlinputelement api: required

  21. htmlselectelement api: required

  22. htmltextareaelement api: required

  23. mediadevices api: getusermedia: secure context required

  24. navigator api: activevrdisplays: secure context required

  25. navigator api: geolocation: secure context required

  26. navigator api: getbattery: secure context required

  27. navigator api: getgamepads: secure context required

  28. navigator api: mediadevices: secure context required

  29. navigator api: registerprotocolhandler: secure context required

  30. navigator api: requestmidiaccess: secure context required

  31. navigator api: useragentdata: secure context required

  32. ndefmessage api: secure context required

  33. ndefreader api: secure context required

  34. ndefreadingevent api: secure context required

  35. ndefrecord api: secure context required

  36. notification api: secure context required

  37. presentationrequest api: secure context required

  38. subtlecrypto api: secure context required

  39. svganimationelement api: requiredextensions

  40. svggraphicselement api: requiredextensions

  41. css selector: `:last-child`: matches elements with no parent

  42. css selector: `:nth-child()`: matches elements with no parent

  43. css selector: `:required`

  44. html element: html: manifest: secure context required

  45. html element: select: required

  46. html element: textarea: required

  47. headers http header: clear-site-data: secure context required

  48. headers http header: set-cookie: `samesite`: secure context required

  49. global_attributes: requiredextensions

  50. global_attributes: requiredextensions: recognizes mathml namespace