1. CSS3 Background-image options

    New properties to affect background images, including background-clip, background-origin and background-size

  2. :optional CSS pseudo-class

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

  3. "once" event listener option

    Causes an event listener to be automatically removed after it gets invoked, so that it only gets invoked once. Similar to jQuery's `$.one()` feature.

  4. X-Frame-Options HTTP header

    An HTTP header which indicates whether the browser should allow the webpage to be displayed in a frame within another webpage. Used as a defense against clickjacking attacks.

  5. cookiestore api: delete: `partitioned` option

  6. cookiestore api: set: `maxage` option

  7. cookiestore api: set: `partitioned` option

  8. credentialscontainer api: get: `identity` option

  9. credentialscontainer api: get: `identity` option: `identity.context`

  10. credentialscontainer api: get: `identity` option: `identity.mode`

  11. credentialscontainer api: get: `identity` option: support for multiple `providers`

  12. credentialscontainer api: get: `identity` option: `identity.providers.domainhint`

  13. credentialscontainer api: get: `identity` option: `identity.providers.fields`

  14. credentialscontainer api: get: `identity` option: `identity.providers.loginhint`

  15. credentialscontainer api: get: `identity` option: `identity.providers.nonce`

  16. credentialscontainer api: get: `identity` option: `identity.providers.params`

  17. credentialscontainer api: get: `otp` option

  18. credentialscontainer api: get: `publickey` option

  19. credentialscontainer api: get: `publickey` option: `get()` extensions

  20. credentialscontainer api: get: `publickey` option: `get()` extensions: `appid` extension

  21. credentialscontainer api: get: `publickey` option: `hints` option

  22. css api: `supports()` static method: parentheses for single-argument version are optional.

  23. gpudevice api: createcomputepipeline: `entrypoint` properties are optional for determined default compute shader entry points.

  24. gpudevice api: createrenderpipeline: `depthcompare` and `depthwriteenabled` properties are optional when not needed (for example, formats without depth).

  25. gpudevice api: createrenderpipeline: `entrypoint` properties are optional for determined default fragment and vertex shader entry points.

  26. gpu api: requestadapter: `featurelevel` option

  27. htmldatalistelement api: options

  28. htmlselectelement api: options

  29. pushsubscription api: options

  30. range api: collapse: `tostart` parameter is optional

  31. response api: `response()` constructor: `body` parameter is optional

  32. rtcrtpscripttransformer api: options

  33. selection api: extend: `offset` parameter is optional

  34. urlpattern api: `urlpattern()` constructor: `ignorecase` option

  35. videodecoder api: configure: `flip` configuration option

  36. videodecoder api: configure: `rotation` configuration option

  37. videoframe api: `videoframe()` constructor: `flip` option

  38. videoframe api: `videoframe()` constructor: `metadata` option

  39. videoframe api: `videoframe()` constructor: `rotation` option

  40. css at-rule: `@container`: `<container-query>` is optional (allows name-only queries)

  41. css property: border-image: optional `<border-image-slice>`

  42. html element: option

  43. html element: option: disabled

  44. html element: option: label

  45. html element: option: selected

  46. html element: option: value

  47. http method: options

  48. javascript operator: optional chaining operator (`?.`)

  49. javascript statement: `try...catch`: optional catch binding