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. cssstylesheet api: `insertrule()`: `index` parameter is optional

  6. document api: createtreewalker: `whattoshow` and `filter` parameters are optional

  7. element api: animate: `options.composite` parameter

  8. element api: animate: `options.id` parameter

  9. element api: animate: `options.pseudoelement` parameter

  10. element api: scroll: `options.behavior` parameter

  11. element api: scroll: `options.left` parameter

  12. element api: scroll: `options.top` parameter

  13. eventtarget api: addeventlistener: `usecapture` parameter is optional

  14. eventtarget api: removeeventlistener: `usecapture` parameter is optional

  15. htmldatalistelement api: options

  16. htmlselectelement api: options

  17. htmltablerowelement api: insertcell: `index` parameter is optional

  18. pushsubscription api: options

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

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

  21. rtcrtpscripttransformer api: options

  22. selection api: collapse: `offset` parameter is optional

  23. selection api: containsnode: `partialcontainment` parameter is optional

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

  25. window api: scrollby: `options.behavior` parameter

  26. window api: scrollby: `options.left` parameter

  27. window api: scrollby: `options.top` parameter

  28. window api: scrollto: `options.behavior` parameter

  29. window api: scrollto: `options.left` parameter

  30. window api: scrollto: `options.top` parameter

  31. window api: scroll: `options.behavior` parameter

  32. window api: scroll: `options.left` parameter

  33. window api: scroll: `options.top` parameter

  34. worker api: `worker()` constructor: `options.name` parameter

  35. worker api: `worker()` constructor: `options.type` parameter

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

  37. html element: option

  38. html element: option: disabled

  39. html element: option: label

  40. html element: option: selected

  41. html element: option: value

  42. http method: options

  43. javascript built-in: bigint: tolocalestring: options

  44. javascript built-in: date: tolocaledatestring: options

  45. javascript built-in: date: tolocalestring: options

  46. javascript built-in: date: tolocaletimestring: options

  47. javascript built-in: number: tolocalestring: options

  48. javascript built-in: string: localecompare: options

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

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