The modern standard API for adding DOM event handlers. Introduced in the DOM Level 2 Events spec. Also implies support for `removeEventListener`, the [capture phase](https://dom.spec.whatwg.org/#dom-event-capturing_phase) of DOM event dispatch, as well as the `stopPropagation()` and `preventDefault()` event methods.
Method of easily manipulating classes on elements, using the `DOMTokenList` object.
Crisp edges/pixelated images
Scales images with an algorithm that preserves edges and contrast, without smoothing colors or introducing blur. This is intended for images such as pixel art. Official values that accomplish this for the `image-rendering` property are `crisp-edges` and `pixelated`.
:focus-visible CSS pseudo-class
The `:focus-visible` pseudo-class applies while an element matches the `:focus` pseudo-class, and the UA determines via heuristics that the focus should be specially indicated on the element (typically via a “focus ring”).
:is() CSS pseudo-class
The `:is()` (formerly `:matches()`, formerly `:any()`) pseudo-class checks whether the element at its position in the outer selector matches any of the selectors in its selector list. It's useful syntactic sugar that allows you to avoid writing out all the combinations manually as separate selectors. The effect is similar to nesting in Sass and most other CSS preprocessors.
selector list argument of :not()
Selectors Level 3 only allowed `:not()` pseudo-class to accept a single simple selector, which the element must not match any of. Thus, `:not(a, .b, [c])` or `:not(a.b[c])` did not work. Selectors Level 4 allows `:not()` to accept a list of selectors. Thus, `:not(a):not(.b):not([c])` can instead be written as `:not(a, .b, [c])` and `:not(a.b[c])` works as intended.
Method of setting a list of options for a user to select in a text field, while leaving the ability to enter a custom value.
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.
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`.
The element generates a block container box, and lays out its contents using flow layout. It always establishes a new block formatting context for its contents. It provides a better solution to the most use cases of the "clearfix" hack.
HEIF/ISO Base Media File Format
HEIF (High Efficiency Image File Format) is a standard developed by the Moving Picture Experts Group (MPEG) for storage and sharing of images and image sequences. Can use `.heif` or `.heic` file extensions.
A security mechanism that allows developers to explicitly enable or disable various powerful browser features for a given site. Similar to [Document Policy](/document-policy).
When the promise is settled, whether fulfilled or rejected, the specified callback function is executed.
A promise represents the eventual result of an asynchronous operation.
Method of using small symbols next to each glyph to emphasize a run of text, commonly used in East Asian languages. The `text-emphasis` shorthand, and its `text-emphasis-style` and `text-emphasis-color` longhands, can be used to apply marks to the text. The `text-emphasis-position` property, which inherits separately, allows setting the emphasis marks' position with respect to the text.
event api: istrusted
external api: issearchproviderinstalled
fetchevent api: isreload
filesystementry api: isdirectory
filesystementry api: isfile
filesystemhandle api: issameentry
htmlelement api: iscontenteditable
htmlimageelement api: ismap
idbindex api: isautolocale
inputevent api: iscomposing
keyboardevent api: iscomposing
mediarecorder api: istypesupported
mediasource api: istypesupported
node api: isconnected
node api: isdefaultnamespace
node api: isequalnode
node api: issamenode
node api: issupported
pointerevent api: isprimary
range api: ispointinrange
scheduling api: isinputpending
selection api: iscollapsed
text api: iselementcontentwhitespace
uievent api: ischar
usbdevice api: isochronoustransferin
usbdevice api: isochronoustransferout
window api: issecurecontext
window api: issecurecontext: considers `window.opener`
xrview api: isfirstpersonobserver
css property: isolation
html element: img: ismap