1. Audio element

    Method of playing sound on webpages (without requiring a plug-in). Includes support for the following media properties: `currentSrc`, `currentTime`, `paused`, `playbackRate`, `buffered`, `duration`, `played`, `seekable`, `ended`, `autoplay`, `loop`, `controls`, `volume` & `muted`

  2. CSS element() function

    This function renders a live image generated from an arbitrary HTML element

  3. CSS Filter Effects

    Method of applying filter effects using the `filter` property to elements, matching filters available in SVG. Filter functions include blur, brightness, contrast, drop-shadow, grayscale, hue-rotate, invert, opacity, sepia and saturate.

  4. ::first-letter CSS pseudo-element selector

    CSS pseudo-element that allows styling only the first "letter" of text within an element. Useful for implementing initial caps or drop caps styling.

  5. Custom Elements (deprecated V0 spec)

    Original V0 version of the custom elements specification. See [Custom Elements V1](#feat=custom-elementsv1) for support for the latest version.

  6. Custom Elements (V1)

    One of the key features of the Web Components system, custom elements allow new HTML tags to be defined.

  7. Customizable Select element

    Customization of the `<select>` element's appearance. Previously envisioned as a separate element (`<selectlist>` or `<selectmenu>`).

  8. Details & Summary elements

    The <details> element generates a simple no-JavaScript widget to show/hide element contents, optionally by clicking on its child <summary> element.

  9. Dialog element

    Method of easily creating custom dialog boxes to display to the user with modal or non-modal options. Also includes a `::backdrop` pseudo-element for behind the element.

  10. Element.closest()

    DOM method that returns the current element if it matches the given selector, or else the closest ancestor element that matches the given selector, or else null.

  11. document.elementFromPoint()

    Given coordinates for a point relative to the viewport, returns the element that a click event would be dispatched at if the user were to click the point (in other words, the element that hit-testing would find).

  12. Scroll methods on elements (scroll, scrollTo, scrollBy)

    Methods to change the scroll position of an element. Similar to setting `scrollTop` & `scrollLeft` properties, but also allows options to be passed to define the scroll behavior.

  13. disabled attribute of the fieldset element

    Allows disabling all of the form control descendants of a fieldset via a `disabled` attribute on the fieldset element itself.

  14. CSS Flexible Box Layout Module

    Method of positioning elements in horizontal or vertical stacks. Support includes all properties prefixed with `flex`, as well as `display: flex`, `display: inline-flex`, `align-content`, `align-items`, `align-self`, `justify-content` and `order`.

  15. Fullscreen API

    API for allowing content (like a video or canvas element) to take up the entire screen.

  16. Element.getBoundingClientRect()

    Method to get the size and position of an element's bounding box, relative to the viewport.

  17. HTML5 semantic elements

    HTML5 offers some new elements, primarily for semantic purposes. The elements include: `section`, `article`, `aside`, `header`, `footer`, `nav`, `figure`, `figcaption`, `time`, `mark` & `main`.

  18. maxlength attribute for input and textarea elements

    Declares an upper bound on the number of characters the user can input. Normally the UI ignores attempts by the user to type in additional characters beyond this limit.

  19. Media Capture from DOM Elements API

    API to capture Real-Time video and audio from a DOM element, such as a `<video>`, `<audio>`, or `<canvas>` element via the `captureStream` method, in the form of a `MediaStream`

  20. Context menu item (menuitem element)

    Method of defining a context menu item, now deprecated and [removed from the HTML specification](https://github.com/whatwg/html/issues/2730).

  21. Picture element

    A responsive images method to control which image resource a user agent presents to a user, based on resolution, media query and/or support for a particular image format

  22. readonly attribute of input and textarea elements

    Makes the form control non-editable. Unlike the `disabled` attribute, `readonly` form controls are still included in form submissions and the user can still select (but not edit) their value text.

  23. CSS user-select: none

    Method of preventing text/element selection using CSS.

  24. wbr (word break opportunity) element

    Represents an extra place where a line of text may optionally be broken.

  25. CSS -webkit-user-drag property

    The non-standard `-webkit-user-drag` CSS property can be used to either make an element draggable or explicitly non-draggable (like links and images). See the standardized [draggable attribute/property](/mdn-api_htmlelement_draggable) for the recommended alternative method of accomplishing the same functionality.

  26. html element: a: url text fragments

  27. html element: base: href: `data:` and `javascript:` urls are not allowed

  28. html element: base: href: relative uris.

  29. html element: h1: no user agent styles in `<article>`, `<aside>`, `<nav>`, and `<section>`.

  30. html element: iframe: allow: usb

  31. html element: img: usemap

  32. html element: img: usemap: content is case-sensitive

  33. html element: object: usemap

  34. html element: u

  35. html element: ul

  36. html element: ul: compact

  37. html element: ul: type

  38. html element: usermedia

  39. elements: semantics: use the algorithm described on mdn to determine the visible child.

  40. svg element: use

  41. svg element: use: load from `data:` uri

  42. svg element: use: load from external uri

  43. svg element: use: height

  44. svg element: use: href

  45. svg element: use: width

  46. svg element: use: x

  47. svg element: use: `xlink:href`

  48. svg element: use: y