1. Audio Tracks

    Method of specifying and selecting between multiple audio tracks. Useful for providing audio descriptions, director's commentary, additional languages, alternative takes, etc.

  2. CSS text-box-trim & text-box-edge

    Provides the ability to remove the vertical space appearing above and below text glyphs, allowing more precise positioning and alignment. Previously specified as the `leading-trim` & `text-edge` properties.

  3. CSS3 Transitions

    Simple method of animating certain properties of an element, with ability to define property, duration, delay and timing function.

  4. Do Not Track API

    API to allow the browser's Do Not Track setting to be queried via `navigator.doNotTrack`. Due to lack of adoption the Do Not Track specification was deprecated in 2018.

  5. PageTransitionEvent

    Fired at the Window when the page's entry in the session history stops being the current entry. Includes the `pageshow` and `pagehide` events.

  6. PNG alpha transparency

    Semi-transparent areas in PNG files

  7. CSS3 2D Transforms

    Method of transforming an element including rotating, scaling, etc. Includes support for `transform` as well as `transform-origin` properties.

  8. CSS3 3D Transforms

    Method of transforming an element in the third dimension using the `transform` property. Includes support for the `perspective` property to set the perspective in z-space and the `backface-visibility` property to toggle display of the reverse side of a 3D-transformed element.

  9. Trusted Types for DOM manipulation

    An API that forces developers to be very explicit about their use of powerful DOM-injection APIs. Can greatly improve security against XSS attacks.

  10. TTF/OTF - TrueType and OpenType font support

    Support for the TrueType (.ttf) and OpenType (.otf) outline font formats in @font-face.

  11. Video Tracks

    Method of specifying and selecting between multiple video tracks. Useful for providing sign language tracks, burnt-in captions or subtitles, alternative camera angles, etc.

  12. View Transitions API (single-document)

    Provides a mechanism for easily creating animated transitions between different DOM states, while also updating the DOM contents in a single step. This API is specific to single-document transitions, support for same-origin cross-document transitions is [being planned](https://github.com/WICG/view-transitions/blob/main/cross-doc-explainer.md).

  13. WebAssembly Non-trapping float-to-int Conversion

    An extension to WebAssembly adding floating-point to integer conversion operators which saturate instead of trapping

  14. WebVTT - Web Video Text Tracks

    Format for marking up text captions for multimedia resources.

  15. trackevent api

  16. trackevent api: track

  17. transitionevent api

  18. transitionevent api: elapsedtime

  19. transitionevent api: propertyname

  20. transitionevent api: pseudoelement

  21. treewalker api

  22. treewalker api: currentnode

  23. treewalker api: filter

  24. treewalker api: firstchild

  25. treewalker api: lastchild

  26. treewalker api: nextnode

  27. treewalker api: nextsibling

  28. treewalker api: parentnode

  29. treewalker api: previousnode

  30. treewalker api: previoussibling

  31. treewalker api: root

  32. treewalker api: whattoshow

  33. trustedhtml api

  34. trustedhtml api: tojson

  35. trustedscript api

  36. trustedscripturl api

  37. trustedscripturl api: tojson

  38. trustedscript api: tojson

  39. trustedtypepolicy api

  40. trustedtypepolicyfactory api

  41. trustedtypepolicyfactory api: emptyhtml

  42. trustedtypepolicyfactory api: ishtml

  43. trustedtypepolicyfactory api: isscript

  44. trustedtypepolicyfactory api: isscripturl

  45. trustedtypepolicy api: createhtml

  46. trustedtypepolicy api: createscript

  47. trustedtypepolicy api: createscripturl

  48. trustedtypepolicy api: name

  49. trustedtypes api

  50. html element: tr