Customized built-in elements are HTML elements that extend built-in elements using the is attribute, to add new behaviors that you define.

Background fetch downloads data in the background even when the web page is closed.

The trackVisibility parameter for the IntersectionObserver constructor enables tracking the visibility of an element, to detect if it may be obscured by other content or visual effects. Also known as IntersectionObserver v2.

The Web Bluetooth API enables selecting and communicating with nearby Bluetooth devices.

The WebUSB API exposes USB compatible devices to web pages.

An element performance entry measures the time to render elements that have the elementtiming attribute.

A longtask performance entry measures tasks that occupy the UI thread for 50 milliseconds or more, a metric for input latency, delayed animations, and other sources of "jank."

The Presentation API shows or controls content on another display, such as a network-connected TV or projector.

The word-break: break-word CSS declaration sets word breaks to occur according to their customary rules.

The <input type="color"> HTML element shows a color picker from which users can choose a color value.

The WebDriver protocol allows out-of-process programs to inspect and control browsers to, for example, run tests of web applications. Also known as WebDriver classic.

The touched property of a GamepadButton object indicates whether a button capable of detecting touch is currently touched.

The ::selection CSS pseudo-element selects text a user has highlighted.

The navigator.connection API provides information about the network connection a device is using and fires events when the connection type changes.

TLS 1.3 sessions may be resumed more quickly by sending so-called early data to servers before the TLS handshake has finished. Also known as zero round-trip time resumption or 0-RTT.

The ping attribute for <a> elements sets a URL to send a POST request to when the <a> is clicked. This is typically used for outbound link reporting.

The PaymentRequest API prompts the user to make a payment through the browser's user interface.

The speak-as CSS property sets how any element's content is spoken. Not to be confused with the speak-as descriptor of @counter-style at-rules.

The <input type="month"> HTML element shows a month picker.

The hand and pose properties of a Gamepad object represent the position in space and the hand that WebVR controllers are held in.

The lr, lr-tb, rl, rl-tb, tb, and tb-rl keyword values for the writing-mode CSS property set the text direction for elements in SVG 1.1 documents.

Touch events touchstart, touchmove, touchend, and touchcancel fire when users interact with a touch-sensitive surface, such as a screen or drawing tablet. These events are similar to mouse events.

The DOM level 2 style specification defined interfaces to access and modify CSS styles, such as CSSValue and CSSPrimitiveValue, that were later excluded from the CSS object model.

The with JavaScript statement adds a given object to the chain of scopes used to evaluate names.

The cross-fade() CSS function generates an image by mixing two images.

The inverted-colors CSS media query sets styles based on whether the user has inverted all colors, such as with mobile accessibility settings.

The Notification() constructor shows a message to the user, typically using the notification system of the host operating system.

The filter() CSS function applies one or more graphic effects to a CSS image, such as a background image. You can use functions, such as blur() and drop-shadow(), alone or combined to produce different effects. For instance, background: filter(url(image.png), blur(2px)).

The MediaSource API is a custom data source for media elements commonly used for adaptive streaming. Also known as Media Source Extensions (MSE).

The substr() method of strings returns part of a string, starting from an index and ending a given number of characters after.