1. CSS Container Queries (Size)

    Size queries in Container Queries provide a way to query the size of a container, and conditionally apply CSS to the content of that container.

  2. CSS Container Style Queries

    Style queries in Container Queries provide a way to query the current styling of a container, and conditionally apply additional CSS to the contents of that container.

  3. CSS Container Query Units

    Container Query Units specify a length relative to the dimensions of a query container. The units include: `cqw`, `cqh`, `cqi`, `cqb`, `cqmin`, and `cqmax`.

  4. CSS Feature Queries

    CSS Feature Queries allow authors to condition rules based on whether particular property declarations are supported in CSS using the @supports at rule.

  5. Media Queries: interaction media features

    Allows a media query to be set based on the presence and accuracy of the user's pointing device, and whether they have the ability to hover over elements on the page. This includes the `pointer`, `any-pointer`, `hover`, and `any-hover` media features.

  6. Media Queries: Range Syntax

    Syntax improvements to make media queries using features that have a "range" type (like width or height) less verbose. Can be used with ordinary mathematical comparison operators: `>`, `<`, `>=`, or `<=`. For example: `@media (100px <= width <= 1900px)` is the equivalent of `@media (min-width: 100px) and (max-width: 1900px)`

  7. Media Queries: resolution feature

    Allows a media query to be set based on the device pixels used per CSS unit. While the standard uses `min`/`max-resolution` for this, some browsers support the older non-standard `device-pixel-ratio` media query.

  8. CSS3 Media Queries

    Method of applying styles based on media information. Includes things like page and device dimensions

  9. High-quality kerning pairs & ligatures

    When used in HTML, the unofficial `text-rendering: optimizeLegibility` CSS property enables high-quality kerning and ligatures in certain browsers. Newer browsers have this behavior enabled by default.

  10. matchMedia

    API for finding out whether or not a media query applies to the document.

  11. Payment Request API

    Payment Request is a new API for the open web that makes checkout flows easier, faster and consistent on shopping sites.

  12. prefers-color-scheme media query

    Media query to detect if the user has set their system to use a light or dark color theme.

  13. prefers-reduced-motion media query

    CSS media query based on a user preference for preferring reduced motion (animation, etc).

  14. querySelector/querySelectorAll

    Method of accessing DOM elements using CSS selectors

  15. requestAnimationFrame

    API allowing a more efficient way of running script-based animation, compared to traditional methods using timeouts. Also covers support for `cancelAnimationFrame`

  16. requestIdleCallback

    API allowing the execution of JavaScript to be queued to run in idle browser time, either at the end of a frame or when the user is inactive. Also covers support for `cancelIdleCallback`. The API has similarities with `requestAnimationFrame`.

  17. Web SQL Database

    Method of storing data client-side, allows SQLite database queries for access and manipulation.

  18. Upgrade Insecure Requests

    Declare that browsers should transparently upgrade HTTP resources on a website to HTTPS.

  19. XMLHttpRequest advanced features

    Updated functionality to the original XHR specification including things like file uploads, transfer progress information and the ability to send FormData. Previously known as [XMLHttpRequest Level 2](https://www.w3.org/TR/2012/WD-XMLHttpRequest-20120117/), these features now appear simply in the XMLHttpRequest spec.

  20. canvasrenderingcontext2d api: quadraticcurveto

  21. css api: `q()` static method

  22. documentfragment api: queryselector

  23. documentfragment api: queryselectorall

  24. document api: querycommandenabled

  25. document api: querycommandindeterm

  26. document api: querycommandstate

  27. document api: querycommandsupported

  28. document api: querycommandvalue

  29. document api: queryselector

  30. document api: queryselectorall

  31. element api: queryselector

  32. element api: queryselectorall

  33. filesystemhandle api: querypermission

  34. gpudevice api: queue

  35. lockmanager api: query

  36. offscreencanvasrenderingcontext2d api: quadraticcurveto

  37. orientationsensor api: quaternion

  38. path2d api: quadraticcurveto

  39. permissions api: query

  40. queuemicrotask api

  41. window api: querylocalfonts

  42. css at-rule: `@container`: style queries for custom properties

  43. css at-rule: `@media`: media query value support

  44. css at-rule: `@media`: nested media queries

  45. css property: quotes

  46. css property: quotes: auto

  47. css property: quotes: none

  48. html element: q

  49. html element: q: cite

  50. regular_expressions: quantifier: `*`, `+`, `?`, `{n}`, `{n,}`, `{n,m}`