The fill-box, stroke-box, and view-box values for clip-path set an edge of the element's box to use as the clipping shape.

The :user-valid and :user-invalid pseudo-classes match form controls that have been marked as valid or invalid based on their validation constraints.

WAI-ARIA attributes have corresponding properties on Element and ElementInternals objects.

The rel="modulepreload" attribute for the <link> HTML element indicates that a module script should be fetched, parsed, and compiled preemptively, and stored for later execution.

The overflow-block and overflow-inline CSS media queries set styles based on the way a device displays content that's larger than the viewport or page area. For example, a laptop lets users scroll to reveal content, while a printer displays overflowing content on additional pages.

The of syntax for the :nth-child() and :nth-last-child() CSS functional pseudo-classes match elements by the relative position of elements, counted from the first or last sibling matching a selector list.

The Oklab color space expresses colors in terms of lightness and how red/green and blue/yellow a color is, aiming to match how humans perceive colors. OkLCh is a variant of Oklab with polar coordinates. These color spaces can be used with the CSS oklab() and oklch() functions.

The range syntax of CSS media queries allows you to use mathematical comparison operators such as <, >, <=, and >= to define a range of values for a media query. For example, (400px < width < 1000px) returns true if the viewport width is between 400px and 1000px.

The messageerror event fires on a target, such as a window or worker, when an incoming message cannot be deserialized. This event can fire for many types of messages, such as cross-document messages or broadcast channel messages.

Notifications via service worker registration's showNotification() method, sent from installed web applications (for example, saved to the Home Screen on Safari for iOS), show a message to the user, typically using the notification system of the host operating system.

The OffscreenCanvas API provides a canvas that can be drawn to off screen, with no dependencies on the DOM, which can be used to run heavy rendering operations inside a worker context.

The navigator.storage.getDirectory() method returns a FileSystemDirectoryHandle that is restricted to a specific origin and invisible to the user's actual file system for faster file-based applications, such as SQLite databases.

The outline CSS shorthand sets the color, style, and width of a line around an element, outside of the border.

MathML, or the Mathematical Markup Language, describes mathematical notation, such as expressions and formulas. Also known as MathML Core.

The offset CSS property animates an element along a defined motion path.

The overflow: clip CSS declaration clips an element's overflowing content to the box that's defined by the overflow-clip-margin property. Unlike overflow: hidden, it allows you to hide overflow on one axis while keeping overflow on the other axis visible.

The :modal pseudo-class selects elements that put other elements into a non-interactive state, such as a fullscreen element or a <dialog> element used with showModal().

The navigator.mediaCapabilities API queries the encoding and decoding abilities of the device, such as supported codecs, resolutions, and bitrates.

The Object.hasOwn() static method checks whether an object has a given property. It's a more robust alternative to the Object.prototype.hasOwnProperty() method.

The navigation performance entry and the PerformanceNavigationTiming API measures navigation events, such as loading time or the number of redirects.

CSS logical properties control borders, size, margin, and padding with directions and dimensions relative to the writing mode. For example, in a left to right, top to bottom writing mode, block-end refers to the bottom. Also known as flow relative.

The MediaRecorder API captures data generated by MediaStream or HTMLMediaElement objects for analysis, processing, or saving to disk. Also known as the Media Recording API.

The OES_fbo_render_mipmap extension for WebGL 1.0 contexts attaches any level of a texture to a framebuffer object.

The OfflineAudioContext API represents an audio processing graph that writes to an AudioBuffer instead of an output device.

The rel="preload" attribute for the <link> HTML element requests resources, such as images or style sheets, that the page needs soon, so the browser may prioritize them for loading before rendering begins.

The :not() functional pseudo-class matches elements that do not match the selectors in its argument.

The logical AND assignment (&&=) and the logical OR assignment (||=) operators short-circuit the respective binary logical operators.

The nullish coalescing (??) and nullish coalescing assignment (??=) operators return (or assign) its right-hand side operand when its left-hand side operand is null or undefined, and otherwise returns its left-hand side operand.

The min() and max() CSS functions return the minimum or maximum of the arguments, while clamp() clamps a value to a given range.

To improve readability for numeric literals, underscores (_) can be used as separators. For example, 1_050.95 is equivalent to 1050.95.

The overflow CSS property sets the behavior for when content doesn't fit in an element.

The getVideoPlaybackQuality() method of HTMLVideoElement returns metrics that can be used to determine the playback quality of a video, such as how many frames were dropped.

The rel="preconnect" attribute for the <link> HTML element is a hint to the browser that the page or user is likely to request resources from another origin, so the browser should preemptively start a connection to the href value's origin.

The :link CSS pseudo-class matches unvisited links, :visited matches visited links, and :any-link matches both.

The mask-type CSS property on an SVG <mask> element sets whether the mask is a luminance or alpha mask.

The min-content and max-content CSS keywords represent the smallest and largest intrinsic sizes of an element.

The mix-blend-mode CSS property blends an element's content with its background or parent elements using blend modes like multiply, difference, or color.

When a document is loaded over HTTPS, browsers ensure that none of the document's resources are loaded over an insecure protocol. Instead, resources that the document attempts to load over an insecure protocol are either loaded over HTTPS or are blocked.

The object-fit CSS property sets how images, videos, and other replaced elements are scaled within their container.

The object-position CSS property places images, videos, and other replaced elements within their boxes.

Omit the binding parameter of a catch clause when you don't need information about the exception in a try ... catch statement.

The <meter> element represents a scalar value within a known range or a fractional value, typically shown as a progress bar.

The OES_vertex_array_object extension for WebGL 1.0 contexts adds vertex array objects (VAOs) which encapsulate vertex array states. These objects keep pointers to vertex data and names for different sets of vertex data.

The navigator.mediaDevices.getUserMedia() API requests access to devices that produce audio or video streams, such as microphones or video cameras.

The outline-color, outline-style, and outline-width and outline-offset CSS properties style a line around an element, outside of the border.

Multi-column layout flows an element's content across one or more columns in a single row, without affecting the display property of its children.

The OES_texture_half_float extension for WebGL 1.0 contexts adds texture formats with 16-bit (also known as half float) and 32-bit floating-point components.

The <link> element creates a relationship between the current document and an external resource, such as a stylesheet or favicon.

The <ol>, <ul>, and <li> HTML elements represent ordered and unordered lists.

The list-style shorthand CSS property and the list-style-image, list-style-position, and list-style-type longhand properties set the position and appearance of a list item's marker.

The localStorage and sessionStorage APIs store data as key-value pairs. While localStorage persists across sessions, sessionStorage data is discarded when the page is closed.

The location global object represents the current page's address. You can use it to get the parts of the address (such as location.hostname or location.pathname) or navigate to another URL.

The <main> element represents the dominant content of a document. It is commonly used together with <header> and <footer>.

Map objects hold key-value pairs and remember the original insertion order of the keys.

The margin CSS property sets space around an element. It is a shorthand for margin-top, margin-right, margin-bottom, and margin-left.

The <mark> element represents text which is marked or highlighted for reference or notation purposes.

The window.matchMedia() method checks whether a media query applies to the document.

The @media CSS rule conditionally applies styles based on the output device type, its capabilities, and the user's preferences. Media queries are composed of an optional media type such as screen or print, and one or more mandatory media features, such as prefers-reduced-animations.

The <menu> element represents an unordered list of action items (<li>), such as a toolbar. It is a semantic alternative to the <ul> element.

The <meta> element represents metadata about the page used by the browser or search engines, including description, keywords, and character sets.

The <meta http-equiv="refresh"> HTML element and the equivalent Refresh HTTP header trigger a page reload or redirect. They apply only when the page is fully loaded, after other HTTP redirects or scripted redirects that might execute before the page is fully loaded.

The min-width, min-height, max-width, and max-height CSS properties set the minimum and maximum size of an element.

Mouse events, such as click, mousedown, or mousemove, fire when users interact with an input or pointing device such as a mouse, trackpad, or touchscreen.

The MutationObserver API watches for changes to the DOM tree and calls a callback function when DOM changes occur.

Some CSS color values can be referenced by name, such as red or limegreen. They stand in for specific RGB color values.

The @namespace CSS rule sets a default namespace or namespace prefix. Namespace prefixes allow CSS selectors to distinguish elements with the same name but different document types, such as the HTML <a> element and the SVG <a> element.

The <nav> element represents a section of a page whose purpose is to provide navigation links, either within the current document or to other documents.

The window.navigator API is a generic global object, under which many other, more interesting APIs are located. It doesn't do anything interesting on its own.

The :nth-child() and :nth-last-child() CSS functional pseudo-classes match elements based on their index within a list of elements. The :first-child and :last-child pseudo-classes match the first and last element in a list, and the :only-child pseudo-class matches an element with no siblings.

The :nth-of-type() and :nth-last-of-type() CSS functional pseudo-classes match elements based on their position among siblings of the same type. The :first-of-type, :last-of-type, and :only-of-type pseudo-classes match the first, last, and only elements of its type.

The number type (and Number object) represents floating-point numbers, such as 42 or -4.201, while the Math API contains mathematical functions and constants. JavaScript can also represent boundless negative and positive values as Infinity or not-a-number as NaN (as in 0 * Infinity).

The <object> element represents an external resource such as a PDF or SVG document. It was historically used for plugins such as Shockwave Flash.

Objects in JavaScript are collections of key-value pairs.

The OES_element_index_uint extension for WebGL 1.0 contexts adds support for gl.UNSIGNED_INT types to WebGLRenderingContext.drawElements().

The OES_standard_derivatives extension for WebGL 1.0 contexts adds the GLSL derivative functions dFdx, dFdy, and fwidth.

The OES_texture_float extension for WebGL 1.0 contexts adds floating-point pixel types for textures.

The OES_texture_float_linear extension for WebGL 1.0 and 2.0 contexts adds linear filtering with floating-point pixel types for textures.

The navigator.onLine property is a boolean for whether the browser is connected to some network (though not necessarily the internet). The online and offline events fire when the connection state changes.

The opacity CSS property sets the transparency of an element.

The fill-opacity, and stroke-opacity SVG attributes and CSS properties control the transparency of a stroke or fill of an SVG element.

The <output> element represents the result of a calculation, user action, or form entry.

The isWellFormed() method of strings returns a boolean indicating if the string contains any Unicode lone surrogates. The toWellFormed() method returns a new string where all lone surrogates are replaced by the Unicode replacement character.

The <search> HTML element is a container that represents the parts of the web page with search functionality.

The contain-intrinsic-size CSS property sets the intrinsic size of an element. When using size containment, the browser will lay out the element as if it had a single child of this size.

The @counter-style CSS at-rule sets custom counter styles for list items. For example, you can use a sequence of specific symbols instead of numbers for an ordered list.

The DeviceMotion and DeviceOrientation events report the movement and orientation of the browser's device in physical space. Note that coordinates can differ noticeably between platforms and devices.

The hyphenate-character CSS property sets the character or string to use at the end of a line before a line break.

The hyphens CSS property controls when long words are broken by line wrapping. Although called hyphens, the property applies to word-splitting behavior across languages, such as customary spelling changes or the use of other characters. Support for non-English languages varies significantly.

The image-set() CSS function provides a set of images at different resolutions or pixel densities, which the browser can pick from, depending on the device capabilities.

The navigator.storage API provides information about the availability and persistence of the data that a site stores on the device, by using APIs such as the Cache API or the IndexedDB API.

The update CSS media query sets styles based on whether and how fast the user's device can modify display after it has been rendered. For example, you can avoid animations on devices that aren't fast enough to display them smoothly.

The subgrid value for the grid-template-columns and grid-template-rows properties allows a grid item to inherit the grid definition of its parent grid container.

The dirname attribute of <textarea> and <input> HTML elements includes the field's writing direction as form data on submission.

The display CSS property accepts multiple keyword values, such as inline flex or block flow, to explicitly set an element's inner and outer layout mode. Also known as 2-value, multi-keyword, or multiple value syntax.

The animation-composition CSS property chooses how to combine animations that affect the same property.

The toReversed(), toSorted(), toSpliced(), and with() methods of arrays and typed arrays return changed copies of arrays. They stand in contrast to methods such as sort() or reverse() that change arrays in place.

The e, pi, infinity, and NaN keywords represent well-defined constants accepted in CSS math functions such as calc().

The Worker() constructor accepts { type: "module" } to load scripts that use import and export. Also known as ECMAScript modules or ESM in workers.

The window.print() method opens the browser's print dialog.

The color() function picks a color from a given color space. Wide gamut color spaces like display-p3 allow showing more vibrant and saturated colors than the standard srgb color space.

The color-mix() function mixes two colors in a given color space and by a given amount. Commonly, lighter or darker variations of a color are created by mixing with white or black.

The CompressionStream and DecompressionStream APIs compress and decompress data using the gzip or deflate formats.

The CIE Lab color space expresses colors in terms of lightness and how red/green and blue/yellow a color is. LCH is a variant of Lab with polar coordinates. These color spaces can be used with the CSS color(), lab(), and lch() functions. Also known as CIELAB and CIELCH.

The sctp object on RTCPeerConnection represents the negotiated SCTP transport. SCTP (Stream Control Transmission Protocol) is the protocol that RTCDataChannel uses.

The createConicGradient() methods draw a conic gradient to a 2D canvas.

The roundRect() methods draw a rounded rectangle to a 2D canvas.

The inert HTML attribute marks an element and its descendants as non-interactive. Inert elements don't get focus or fire click events.

The CSSStyleSheet constructor creates a new stylesheet which can be shared between a document and multiple shadow roots using adoptedStyleSheets.

The font-synthesis-small-caps CSS property sets whether or not the browser should synthesize small caps typefaces when they're missing from the font.

The font-synthesis-style CSS property sets whether or not the browser should synthesize italic and oblique typefaces when they're missing from the font.

The font-synthesis-weight CSS property sets whether or not the browser should synthesize bold typefaces when they're missing from the font.

Custom elements may act like built-in form elements, via the attachInternals() method of HTMLElement and the ElementInternals API.

A <script type="importmap"> HTML element provides an import map as a JSON string. An import map controls how the browser should resolve module specifiers when importing JavaScript modules.

The navigator.pdfViewerEnabled property is a boolean for whether the browser navigates to and shows a PDF in the browser window or downloads the PDF.

The Push API subscribes to and receives server-initiated messages. Subscribers receive pushed messages in the background, even after periods inactive or offline.

The requestAnimationFrame() method in workers schedules a function that runs before the next repaint. Together with offscreen canvas, you can animate content from a worker.

The decodedBodySize, encodedBodySize, and transferSize properties of the PerformanceResourceTiming API reports the size of resources loaded.

The screen.orientation API gets information about the orientation of the viewport, such as landscape or portrait. With this API, you can adapt an application's layout or behavior in response to changes in orientation.

The serverTiming property of the PerformanceResourceTiming API contains server timing information about network requests.

The assign() method for <slot> elements assigns nodes to the slot, as an alternative to using the slot and name HTML attributes. The nodes must be children of a shadow host and the shadow root must be created with the slotAssignment set to "manual". Also known as manual slot assignment.

128-bit SIMD (Single Instruction Multiple Data) performs one instruction on multiple units of data, when running on hardware that supports such instructions. Also known as vector instructions.

The translate HTML attribute marks whether an element's text should be translated.

The font-variant-alternates CSS property, along with the @font-feature-values at-rule, chooses when to use a font's alternate glyphs.

The sin(), cos(), tan(), asin(), acos(), atan(), and atan2() CSS functions compute various trigonometric functions.

The color-gamut media query sets styles based on the colors a device can display.

Container size queries with the @container at-rule apply styles to an element based on the dimensions of its container.

The OES_draw_buffers_indexed extension for WebGL 2.0 contexts allows you to control blending on a per-color basis when writing to multiple color buffers simultaneously.

The sv*, lv*, and dv* CSS viewport units are relative to the smallest, largest, and current (dynamic) viewport size. They are used to size elements in relation to the viewport's dimensions.

The font-palette CSS property selects a color palette from the font, optionally overriding individual colors in the @font-palette-values at-rule.

Grid animation allows you to animate the grid-template-columns and grid-template-rows CSS properties.

The ic CSS length unit corresponds to the width of CJK ideographic characters.

The contain: inline-size CSS declaration prevents the element's inline dimension from being set by the element's contents. This permits the browser to avoid slower layout calculations.

The forced-colors CSS @media rule detects when a user has chosen to use a forced colors mode, also known as high-contrast mode, and the forced-color-adjust CSS property sets whether forced colors apply to an element.

The navigator.permissions API checks whether a permission, such as access to geolocation data, has been granted.

The resolution CSS media query sets styles based on the pixel density, or how many pixels a device uses to display a single CSS pixel.

The text-align-last CSS property sets the alignment of the last line of text before a forced line break.

The findLast() and findLastIndex() methods of arrays and typed arrays search an array in reverse order for the first item that satisfies a test function.

The translate, rotate, and scale CSS properties apply single transformations independently, as opposed to applying multiple transformations with the transform CSS property.

The contain: style CSS declaration permits the browser to avoid slower layout calculations by preventing modification to counter (counter-increment and counter-set) and quotation styles (content property quote values) beyond the element's descendants.

The streams API creates, composes, and consumes continuously generated data.

The prefers-contrast CSS media query sets styles based on whether the user prefers more or less contrast, the difference between foreground and background colors.

The dynamic-range CSS media query sets styles based on whether a device can display at least standard range colors or at least high range colors. Non-visual devices will match neither.

Exceptions break the normal control flow of execution to represent exceptional behavior, such as an error. You can respond to the exception in JavaScript code.

The hwb() CSS function picks colors using hue, whiteness, and blackness channels.

The appearance CSS property controls the appearance of form controls. Using appearance: none disables any default native appearance and allows the elements to be styled with CSS.

The at() method of arrays and typed arrays returns the item at an index, including negative indices for getting items relative to the end of an array. Also known as the relative indexing method.

The ::backdrop CSS pseudo-element is a box underneath an element in the top layer, such as a <dialog>. It can be used to create obscuring effects distinguishing a modal element from the elements underneath.

The BroadcastChannel API allows you to send messages between same-origin browsing contexts, such as between the same page loaded in multiple tabs.

The @layer CSS at-rule avoids specificity conflicts by providing priority levels for different groups of CSS rules, such as low-priority styles like resets, and high-priority styles like UI components.

The contain CSS property sets limits to the scope of styles, layout, and paint rendering for speed and efficiency. The none keyword value disables containment, strict is equivalent to contain: size layout style paint, and content is equivalent to contain: layout style paint.

The contain: layout CSS declaration isolates the inside of an element such that it cannot affect the layout of the rest of the page or be affected by the rest of the page. This permits the browser to avoid slower layout calculations.

The contain: paint CSS declaration prevents an element's descendants from being drawn outside the boundaries of the containing element, with any overflow clipped. This permits the browser to avoid slower painting calculations.

The contain: size CSS declaration sets an element's dimensions exclusively by its height and width properties, ignoring its contents and descendants. This permits the browser to avoid slower layout calculations.

The <dialog> HTML element represents a modal or non-modal dialog box, such as a confirmation prompt or a subwindow used to enter data.

The :focus-visible CSS pseudo-class selects elements that match the :focus pseudo-class and meets the browser's criteria for visually emphasizing focused elements.

The navigator.hardwareConcurrency property is the number of logical processors available to run threads on the user's computer.

The scroll-behavior CSS property controls whether scrolling is smooth or snaps, for scroll actions not performed by the user such as those triggered by navigation.

The at() method of strings returns the character (one UTF-16 code unit) at an index, including negative indices for getting the character relative to the end of the string. Also known as the relative indexing method.

The structuredClone() global method creates a deep copy of an object. Values that cannot be cloned can instead be transferred, making the original value no longer usable.

The text-combine-upright CSS property displays multiple characters in the space of a single character in vertical text. This is used in East Asian documents to display Latin-based strings such as components of a date or letters of an initialism.

The text-decoration-skip-ink CSS property sets whether underlines and overlines may be interrupted where the line would cross a glyph.

The transform CSS property and its 3D transform functions allow rotations and other transforms in three dimensions, including perspective transforms.

The navigator.locks API coordinates work with shared resources through mutually exclusive ownership of a resource's name. Also known as web locks.

The text-emphasis CSS property sets position and style for text emphasis marks, especially for East Asian languages.

The color-scheme CSS property sets which color schemes (light or dark) an element uses and may prevent automatic dark mode adjustments by the browser.

The font-synthesis CSS shorthand property disables all font synthesis except the given kinds. To disable a specific kind of font synthesis, instead use the longhand properties such as font-synthesis-style and font-synthesis-weight.

The SharedArrayBuffer object represents bytes shared between multiple workers and the main thread. The Atomics object safely accesses SharedArrayBuffer data to make sure predictable values are read and written and that operations are not interrupted.

Threads in WebAssembly run code in parallel, while atomic memory instructions can guarantee that no two threads can read or write to shared memory at the same time.

The inputmode global HTML attribute gives a hint about what type of data is to be entered into an <input> element, such as text, numeric, or email, so the browser may help the user enter data using an adapted input mechanism, such as an on-screen virtual keyboard.

The externref type can be both a value type and a table element type, while funcref can be a value type.

The enterkeyhint global HTML attribute sets the label for a virtual keyboard's Enter key. For example, enterkeyhint="search" may label the key with a magnifying glass icon.

The fit-content CSS keyword expands a box as needed to fit its contents until the maximum size is reached, preserving the content's preferred aspect ratio.

Bulk memory operations, such as copy and init, mirror the efficiency of native memcpy and memmove operations.

Saturating floating-point to integer conversion operators return the maximum or minimum integer value on overflow instead of trapping.

The image-rendering CSS property sets how images are scaled, retaining smoothness for photos, or hard edges for pixel art and QR codes.

The aspect-ratio CSS property controls the width-to-height ratio of elements. For <img> and <video> elements, the width and height attributes used together with height: auto control the aspect ratio while the image/video is loading.

The BigInt64Array and BigUint64Array typed arrays represent 64-bit integers, signed and unsigned respectively.

The cause property of errors records the specific original cause of the error, particularly for errors that have been re-thrown.

The EXT_color_buffer_float extension for WebGL 2.0 contexts adds color-renderable floating point formats to renderbufferStorage().

The IndexedDB API is a local storage transactional object database.

The Referrer-Policy HTTP header and referrerpolicy HTML attributes control whether requests have the Referer header and what information the header contains.

The WEBGL_color_buffer_float extension for WebGL 1.0 contexts adds the 32-bit floating-point type RGBA32F as a color-renderable format.

The WebGL2RenderingContext API is the "webgl2" rendering context for the <canvas> element. It represents a space for drawing two- and three-dimensional graphics and animations. It corresponds to OpenGL ES 3.0.

The font-family: system-ui CSS declaration uses the operating system default font for text.

The web authentication API allows you to create public key-based credentials and use them for authentication, such as when signing in. Also known as WebAuthn.

The tab-size CSS property sets the width of the tab character.

The visualViewport API provides a way to query and modify the user-visible viewport of a web page.

The AudioWorklet API runs module code in a separate thread, specifically for non-blocking, low latency audio processing.

The ::file-selector-button CSS pseudo-element selects the button of a <input type="file"> element.

The gap CSS property in a flexbox layout sets the size of the space between items.

The <input type="date"> and <input type="time"> HTML elements show date and time pickers.

The Intl.DisplayNames API provides localized names of language, region, script, and currency codes.

The Intl.ListFormat API creates a locale-aware formatter that turns iterable objects into localized strings.

The paint performance entry and the PerformancePaintTiming API measures the duration of "paint" (also called "render") operations as a page loads. The API measures the time to First Paint (FP) and First Contentful Paint (FCP), common metrics for perceived loading times.

The quotes CSS property sets the quotation marks inserted via the content CSS property or <q> element.

Integer values pass bidirectionally between JavaScript and WebAssembly, converted to i64 values in WebAssembly or BigInt values in JavaScript.

Sign-extension operator instructions extend the width of 8-bit, 16-bit, and 32-bit values to 32-bit and 64-bit values.

The WeakRef and FinalizationRegistry objects hold references to garbage-collectable objects without creating strong references that prevent their garbage collection.

The Web Audio API creates graphs of audio nodes that handle sound inputs, synthesize sounds, apply effects, create visualizations, and output to audio devices.

The clip-path CSS property and SVG attribute set the visible area of an element. Everything outside the area will be hidden.

The :is() CSS functional pseudo-class takes a selector list as its argument, and matches any element that can be selected by one of the selectors in that list.

The :where() CSS functional pseudo-class takes a selector list as its argument, and matches any element that can be selected by one of the selectors in that list. It is functionally equivalent to the selectors in the list, but doesn't affect the CSS rule specificity.

The text-underline-offset CSS property shifts underlines on text from the initial position by a given distance. The initial position is affected by the text-underline-position property.

The conic-gradient() and repeating-conic-gradient() CSS functions create backgrounds that progress between two or more colors around a center point.

Instructions and blocks can produce multiple result values.

The BigInt JavaScript type represents integers of any size, including integers too large for the primitive Number type.

The EXT_color_buffer_half_float extension for WebGL 1.0 and 2.0 contexts renders 16-bit floating-point color buffers.

The Intl.Locale API parses Unicode locale identifiers, with language, region, and script codes, such as zh-Hans-CN or en-GB.

The Intl.RelativeTimeFormat API creates a locale-aware formatter that turns an object representing a relative time (such as '1 day ago') into a localized string.

The Promise.any() static method returns a promise that fulfills as soon as the first of an iterable of promises fulfills, with that promise's value. Otherwise, it rejects with an AggregateError when all of the promises have rejected.

The scroll() and scrollBy() methods change the scroll position of overflow content within an element. Similar to setting scrollTop and scrollLeft properties, but with options setting whether the scroll should animate smoothly or jump. Note that scrollTo() is an alias for scroll().

The steps() CSS easing function divides an animation or transition into equidistant intervals, jumping from value to value. The step-start and step-end keyword values are presets with a single interval.

The text-orientation CSS property sets the how text is typeset within a line when the writing mode is vertical.

The web animation API programmatically creates, inspects, and controls element animations, to change and synchronize appearance over time.

The WEBGL_debug_shaders extension for WebGL 1.0 and 2.0 contexts adds the getTranslatedShaderSource() method to debug shaders from privileged contexts.

The WebP image format is a raster graphics file format that supports animation, alpha transparency, and lossy as well as lossless compression.

The replaceAll() method of strings returns a new string where all matches of a pattern (a string or regular expression) have been substituted with a replacement string.

The column-span CSS property controls whether a child element extends across all columns of a multi-column parent.

The line-break CSS property sets how strictly to apply rules for wrapping text to new lines, especially for symbols and punctuation.

Pointer events, such as pointerdown, and the PointerEvent API, represent general pointing inputs, from a wide range of devices, such as a mouse, pen or stylus, or touch with one or more fingers. Not to be confused with the pointer-events CSS property.

The Promise.allSettled() static method waits for an array of promises to settle (resolve or reject).

The queueMicrotask() method schedules a function to run after the currently running synchronous JavaScript finishes but before returning to the event loop.

The :read-only and :read-write CSS pseudo-classes match elements that are read-only or read-write, respectively. For example, :read-only matches <input> and <textarea> elements with the readonly attribute.

The ResizeObserver API observes and reacts to changes in the size of DOM elements.

The part and exportparts HTML attributes expose elements of a shadow DOM as named parts, which can be selected by the ::part() CSS pseudo-element for styling.

The text-underline-position CSS property sets the position of underlines on text. For example, text-underline-position: under places the underline below the text, avoiding crossing descenders. The underline may be further adjusted by the text-underline-offset property.

The revert CSS keyword resets any property to its previous default, provided by either the user or browser stylesheets. For example, setting display: revert on a <div> will likely result in display: block, the browser default style. This is often confused with initial.

The image-orientation CSS property corrects the rotation of an image using the image's metadata, such as EXIF.

The font-optical-sizing CSS property sets whether text rendering is optimized for viewing at different sizes.

The #! comment at the absolute start of a script or module is treated as a normal comment and is ignored by the JavaScript engine.

The Q CSS length unit is an absolute length anchored to the physical measurement of quarter-millimeters. 1Q is equivalent to 1/40 of 1 centimeter.

Mutable global variables are importable and exportable.

The EXT_sRGB extension for WebGL 1.0 contexts adds sRGB support to textures and framebuffer objects.

The all CSS property is a shorthand for all CSS properties, except for direction and unicode-bidi. It accepts only the keywords for explicit defaulting (such as initial and inherit), since they are the only values supported on all CSS properties.

The flat() and flatMap() methods for arrays creates a new array such that each nested array item is concatenated into it.

Async generator functions (async function*) create iterators that return multiple promises, one after another, on-demand.

Asynchronous iterator objects, such as those returned by promises or generator functions, are iterable with the for await .. of loop.

Autonomous custom elements are HTML elements with a hyphenated tag name (like <example-element>) that have behaviors you define.

The background-blend-mode CSS property blends an element's background image and background color using blend modes like multiply, difference, or color.

The <bdi> element isolates text that may have a different text direction from its surrounding text. This prevents the browser's bidirectional text algorithm from affecting or being affected by the direction of the surrounding text.

The captureStream() method for <canvas> elements returns a MediaStream which includes a CanvasCaptureMediaStreamTrack representing real-time video of the canvas image. You can use this to record the canvas, or send it elsewhere, such as another canvas or WebRTC connection.

The caret-color CSS property sets the color of the text insertion pointer in a text input.

The i identifier in a CSS attribute selector matches attribute values case-insensitively in document languages like XML where attribute values are case-sensitive.

The clip-path property can be animated using CSS transitions and animations.

COLRv0 is a font format that supports multi-color glyphs. COLRv0 supports only solid colors.

The navigator.credentials API provides generic storage for authentication credentials. Other credential APIs represent specific kinds of credentials, such as password or public key credentials, that the credential management API stores.

The CSS.escape() static method escapes a string so that it can be used in a valid CSS selector.

The CSS.supports() static method returns whether the browser supports a CSS declaration (given by two arguments, a property and value) or an @supports at-rule condition string.

The :default CSS pseudo-class matches the default element in a group of related form controls, such as checkboxes and radio buttons with the checked attribute.

The destructuring assignment syntax is a JavaScript expression that unpacks values from arrays, or properties from objects, into distinct variables.

The <details> element is a disclosure widget which can be expanded to reveal additional content. When closed, only the nested <summary> element is visible.

The display: flow-root CSS declaration sets an element as the root element of a new flow layout for its children, preventing margin collapse with sibling elements.

The DOMMatrix, DOMPoint, DOMQuad and DOMRect APIs represent points, rectangles, quadrilaterals and transformation matrices within JavaScript. They can be used in transformations in CSS, <canvas>, and SVG.

The dominant-baseline CSS property sets the specific baseline used to align an elements's text and inline-level contents.

The document.elementFromPoint() and document.elementsFromPoint() methods find the top-most element at a given point in the viewport, or all elements at a given point in the viewport, respectively.

The <embed> element represents an external resource such as a PDF or SVG document. It was historically used for plugins such as Shockwave Flash.

The File API represents and reads from file data and metadata. Typically, you get files through other APIs, such as the <input type="file"> element or drag-and-drop events. You may also send file data to other APIs, such as creating images or drawing on canvases.

The :focus-within CSS pseudo-class matches an element if the element or any of its children are focused.

The font-display CSS descriptor sets whether to show a substitute font or nothing while a font face loads. The property manages what's known as a flash of unstyled text or flash of invisible text.

The font-kerning CSS property sets whether kerning data from a font is used to adjust the space between letters.

The document.fonts API dynamically loads custom fonts and tracks when fonts are loading or ready to use.

The font-stretch CSS property selects a font face from a font family based on width, either by a keyword such as condensed or a percentage.

The font-variant-caps CSS property sets whether text should be displayed in small caps, petite caps, or with capital letters designed for titles.

The font-variant-east-asian CSS property controls glyph substitution and sizing in East Asian text.

The font-variant-ligatures CSS property sets how characters can be visually combined for readability or stylistic reasons.

The font-variant-numeric CSS property sets how numeric characters are displayed. For example, you can align columns of numbers or use zeroes that have a slash.

The globalThis property accesses the global this value (and hence the global object itself) across environments.

The :host CSS pseudo-class selects the containing element of the shadow tree in which it is used. The :host() CSS pseudo-class selects the that element only if it matches the provided selector.

The hsl() and hsla() CSS functions pick colors using hue, saturation, lightness, and alpha (transparency) channels.

The srcdoc attribute for the <iframe> HTML element sets a string of HTML to embed in the document. The value of srcdoc overrides loading a document from the src attribute.

The ImageBitmapRenderingContext API is the "bitmaprenderer" rendering context for the <canvas> element. It is commonly used to transfer frames from an OffscreenCanvas to a user-visible <canvas> element.

The :indeterminate CSS pseudo-class selects any form element whose state is indeterminate, such as checkboxes that have been set to an indeterminate state with JavaScript, or radio buttons which are members of a group in which all radio buttons are unchecked.

The input event fires when a form control changes or an element with the contenteditable attribute changes.

The isolation CSS property creates a new stacking context, which impacts z-index ordering and blend modes.

The unicode-bidi and direction CSS properties override the Unicode layout algorithm. They are intended for Document Type Definition (DTD) designers. For HTML documents, you should use the dir global HTML attribute and <bdo> HTML element instead.

The ::placeholder CSS pseudo-element selects help text in <input> and <textarea> elements when no value is set.

The :placeholder-shown CSS pseudo-element selects <input> and <textarea> elements when no value is set and the element's placeholder attribute is not empty. Not to be confused with ::placeholder, which selects the placeholder text itself.

The PNG (Portable Network Graphics) image format is a raster graphics file format with animation, alpha transparency, and lossless compression.

The prefers-color-scheme CSS media query sets styles based on the requested color scheme, light or dark.

The prefers-reduced-motion CSS media query sets styles based on whether the user prefers to minimize the amount of non-essential animations on the device, such as scrolling, panning, zooming, and strobing.

The rgb(), rgba(), and hexadecimal (as in #004488ff) notations pick colors using red, green, blue, and alpha (transparency) channels.

The safe-area-inset- CSS environment variables represent a rectangle that cannot cut off content within a non-rectangular screen. For example, top:\ env(safe-area-inset-top); positions the top of an element below the notch on an iPhone.

The :scope CSS pseudo-class matches the scoping root, for instance the element that querySelector() is called on, or the root of a DOM subtree specified with @scope.

The scrollIntoView() method scrolls an element's ancestor containers such that the element is visible to the user.

CSS scroll snap controls the panning and scrolling behavior within a scroll container.

The EventSource API creates a connection to a server and listens to a stream of events sent by the server.

Shadow DOM allows you to attach encapsulated "shadow" DOM trees to elements. A shadow DOM tree is a separate component, isolated from the scripts and styles in other parts of the document. This is a part of Web Components.

The shape-outside CSS property, along with shape-margin and shape-image-threshold, sets the shape around which adjacent content will wrap.

The circle(), ellipse(), inset(), and polygon() CSS shape functions create shapes for use with clip-path and shape-outside.

The <slot> HTML element is a placeholder inside a web component where consumers of the component can insert their own markup.

The <animate>, <animateMotion>, and <animateTransform> SVG elements declaratively animate SVG elements. Also known as SMIL.

The Sourcemap HTTP response header links generated code to a source map, so the browser shows the original source in a debugger. This makes it easier to work with minified or transpiled code.

The spread (...) syntax allows an iterable, such as an array or string, to be expanded in places where zero or more arguments (for function calls) or elements (for array literals) are expected.

Stable array sort() function

The matchAll() method of strings matches a string against a regular expression and returns an iterator of all results, including capturing groups.

The trimStart() and trimEnd() methods of strings return a new string with whitespace removed from the beginning or end of the string.

The SVG image format, represented by the <svg> element, creates two-dimensional vector graphics with declarative or scripted interaction and animation.

Template literals are literals delimited with backtick (`) characters, allowing for multi-line strings, string interpolation with embedded expressions, and special constructs called tagged templates.

The TextEncoder API transforms a stream of code points into a byte stream with UTF-8 encoding, and TextDecoder does the reverse.

The WEBGL_compressed_texture_astc extension for WebGL 1.0 and 2.0 contexts adds the Adaptive Scalable Texture Compression format to compressedTexImage2D() and compressedTexSubImage2D().

The WebRTC API establishes real-time communication channels directly between browsers. It is commonly used in video conferencing applications.

The RTCPeerConnection.getStats(), RTCRtpSender.getStats(), and RTCRtpReceiver.getStats() methods return detailed information about the status, performance, network, and media for a given WebRTC connection.

The VTTCue API updates various aspects of cues dynamically, such as alignment, size and position.

The will-change CSS property gives hints to the browser about expected changes to an element's scroll position, contents, or style. These hints allow browsers to optimize for upcoming style changes.

The download attribute for <a> elements loads the target URL as a file to be saved, instead of navigating to it. An optional attribute value sets a default file name.

The Intl.PluralRules API creates a locale-aware object that tells you which of the language's pluralization rules apply based on a given number.

An alternative to @media print queries, the beforeprint and afterprint events allow you to change the page for printing and restore the page after printing.

The position: sticky CSS declaration positions an element in the normal flow until it crosses a specified threshold, at which points it becomes fixed (stuck) at that position.

The touch-action CSS property sets whether an element on a touch screen can be panned or pinched to zoom.

If you construct a fetch request with an AbortSignal, you can cancel the request.

The AbortController and AbortSignal APIs allow you to cancel an ongoing operation, such as a fetch() request.

The mediaKeys property of HTMLMediaElement and the navigator.requestMediaKeySystemAccess() method control the playback of content subject to digital rights management. Also known as EME.

The IntersectionObserver API asynchronously observes changes in the intersection of a target element with an ancestor element or with a top-level document's viewport.

In printed page layouts, the break-after, break-before, break-inside CSS properties control where printed pages start and end. Also known as pagination or page breaking.

Methods that validate form controls before submission, such as checkValidity(), reportValidity() and setCustomValidity().

The pointer, any-pointer, hover, and any-hover CSS media queries set styles based on the presence of pointing devices and their ability to hover over elements. For example, most smartphones match the (hover: none) and (pointer: coarse) media query.

The -webkit-device-pixel-ratio, -webkit-min-device-pixel-ratio, and -webkit-max-device-pixel-ratio CSS media queries are standardized compatibility alternatives to resolution media queries.

The overflow-wrap CSS property breaks a line of text onto multiple lines inside the targeted element in an otherwise unbreakable place to prevent overflow. The legacy property is word-wrap.

The promise finally() method executes a function when the promise settles (resolves or rejects).

The tabindex HTML attribute make an element focusable, and sets the element's relative ordering for sequential focus navigation.

The font-variation-settings CSS property sets an "axis of variability" on a variable font, such as weight, optical size, or a custom axis defined by the typeface designer. When possible, use other CSS font properties, such as font-weight: bold. Also known as variable fonts.

The SpeechSynthesis API converts text to speech with artificial voices.

Arrays are iterable with the for … of statement and enumerable with the methods entries(), keys(), and values().

JavaScript modules allow code to be organized into reusable units. Modules use import to load other modules and export to declare what is available to import from other modules. In HTML, modules are loaded with <script type="module">.

The EXT_blend_minmax extension for WebGL 1.0 contexts adds two blend equations, the minimum and maximum color components of the source and destination colors.

The service worker of a website is a script that runs in its own thread and which acts as local proxy that intercepts network requests from the website. Use a service worker to implement advanced caching strategies, offline support, background tasks, or push notification support on your website.

Subresource integrity verifies that a resource, such as script served from a content delivery network, matches a known cryptographic hash. Also known as SRI.

The Upgrade-Insecure-Requests HTTP request header tells the server that the response should redirect to a secure (HTTPS) resource.

The WEBGL_lose_context extension for WebGL 1.0 and 2.0 contexts simulates losing and restoring a WebGLRenderingContext or WebGL2RenderingContext.

The navigator.sendBeacon() method asynchronously sends an HTTP POST request with a limited amount of data, typically for app state, events, and analytics data. The one-way beacon is guaranteed to be initiated before the browser unloads the page, but the sender does not get to handle the response.

The isSecureContext global property is a boolean for whether the current browsing context is secure. This is primarily a check that the page has been served over an HTTPS URL.

The spellcheck global HTML attribute sets whether the browser may check an element for spelling errors.

The <data> element links a given piece of content with a machine-readable translation.

The <time> HTML element represents a time, such as a calendar date, clock time, or duration. It may include the datetime attribute to translate dates into machine-readable format.

CSS grid is a two-dimensional layout system, which lays content out in rows and columns.

The vw, vh, vmin, and vmax CSS viewport units are relative to the size of the viewport, and are used to size elements in relation to the viewport's dimensions.

The WebAssembly.instantiate() and WebAssembly.instantiateStreaming() global static methods load WebAssembly code (also known as Wasm), a portable binary instruction format.

The Intl API provides language sensitive string comparison, number formatting, date and time formatting, and more.

Brotli is a lossless data compression algorithm. When used as a content encoding, it often provides better compression than gzip.

PerformanceResourceTiming entries report when network events happen while loading a resource, such as when connections start and end. You can use this information to measure loading times.

The compositionstart, compositionupdate, and compositionend events fire when an input method editor adds characters that might not be commonly available on keyboards. Examples of these characters are emoji, logograms in Asian languages, or input from speech recognition processors.

The WEBGL_debug_renderer_info extension for WebGL 1.0 and 2.0 contexts exposes information about the graphics driver for debugging purposes.

The async and await keywords allow you to use the asynchronous, promise-based behavior of a function without using promise chains.

Custom properties are CSS properties prefixed with -- that set values you can reuse with the var() function. For example, you can set a --key-color property to reuse as border-color: var(--key-color). Also known as CSS variables.

The font-feature-settings CSS property sets low-level OpenType feature tags for a font. When possible, use font-variant instead.

The padStart() and padEnd() methods of strings return a string lengthened to a minimum number of characters by adding characters to the start or end of the string.

The -webkit-text-stroke-width and -webkit-text-stroke-color CSS properties set the thickness and color of text outlines. The -webkit-text-fill-color sets the color within text character outlines. Both default to the text color.

The "copy", "cut", and "paste" events fire on elements when the user starts an action with the clipboard.

The exponentiation (**) operator returns the result of raising the first operand to the power of the second operand.

The fetch() method makes asynchronous HTTP requests.

The navigator.getGamepads() API accesses and responds to signals from game controllers.

The srcset and sizes attributes for <img> elements set a list of possible sources for the image and a corresponding list of size conditions for choosing a source, to show a responsive image that fits the size of the display.

The writing-mode CSS property sets whether text is laid out horizontally or vertically, and left to right, or right to left.

The <input type="range"> element represents a slider for choosing an inexact value between a minimum and maximum value.

The column-fill CSS property sets the distribution of content across columns in a multi-column layout.

The Selection API controls and modifies user text selections within the page.

The border-image CSS property draws an image around an element.

The copyWithin() method of arrays and typed arrays shifts or copies items of an array to another index of the array without changing its length.

The fill() method of arrays and typed arrays sets all or some items of an array to a given a value.

The find() and findIndex() methods of arrays and typed arrays search an array for the first item that satisfies a test function.

The Array.from() and typed array .from() static methods copy items from an iterable or array-like object to make a new array.

The includes() method of arrays and typed arrays returns whether a given value appears in the array.

The Array.of() and typed array .of() static methods create new arrays from the values of any number of arguments.

The background-repeat CSS property sets how a background image is tiled.

The atob() and btoa() global functions encode and decode strings to and from base 64, respectively.

The @font-face CSS at-rule creates a custom font-family value. The at-rule's descriptors set the font's name, source, and various display settings.

Generator functions (function*) create iterators that return multiple values, one after another, on-demand.

The let and const declarations define block-scoped variables.

The Proxy and Reflect JavaScript built-ins intercept and define custom behavior for fundamental language operations (such as property lookup, assignment, enumeration, or function invocation).

The normalize() method of strings returns a Unicode normal form of a string as a new string. More than one code point sequence can represent the same characters. You can use the normalize() method to find canonically or compatibly equivalent strings.

The @supports (-webkit-transform-3d) CSS media query is a standardized compatibility alternative to @supports (transform-style).

Typed array iteration methods

Typed arrays are iterable with the for … of statement and enumerable with the methods entries(), keys(), and values().

The navigator.userAgent property and several others loosely identify a browser. Selectively showing content based on the user agent string, also known as user agent sniffing, is unreliable. Consider using feature detection or user agent client hints instead.

The filter CSS property applies one or more graphic effects to an element. You can use filter functions, such as blur() and drop-shadow(), alone or combined to produce different effects. For instance, filter: blur(2px).

Content Security Policy (CSP) helps to mitigate certain security threats, including cross-site scripting (XSS) and clickjacking attacks. It consists of a set of directives from a website to a browser, which instruct the browser to restrict the things that the site is allowed to do.

The ANGLE_instanced_arrays extension for WebGL 1.0 contexts draws the same object multiple times or groups of similar objects multiple times, if the group shares the same vertex data, primitive count and type.

The EXT_texture_filter_anisotropic extension for WebGL 1.0 and 2.0 contexts adds anisotropic filtering (AF). AF improves the quality of mipmapped texture access when viewing a textured primitive at an oblique angle.

The DOMParser API parses XML or HTML source code from a string into a DOM Document.

The <picture> element is used for art direction in responsive images, where a different image is displayed based on the <source> element.

The unset keyword resets any CSS property, removing any values previously set by the author, user, or browser. Inherited properties (like color) reset to the parent element's computed value. Non-inherited properties (like display) reset to the specified initial value (inline).

Classes are an object-oriented syntax for JavaScript prototypes.

The initial keyword resets any CSS property to its initial value as defined by the specification. For example, the initial value of the display property is inline, regardless of the element being styled. Not to be confused with revert, which resets to the user or browser default style.

The <template> HTML element holds HTML fragments which you can clone and insert into the document using JavaScript.

The animation CSS property animates an element's style over time, using keyframes described in @keyframes rules.

The CSS object model API reads, creates, and modifies CSS stylesheets and inline styles. Also known as CSSOM.

Flexbox is a one-dimensional layout system, which places content either horizontally or vertically, with optional wrapping.

The HTTP/2 protocol is a major revision of the HTTP network protocol, providing improved performance and efficiency by using a single TCP connection to send multiple streams of data at once.

The codePointAt() method returns the numeric value of the UTF-16 code point at an index of the string. The fromCodePoint() method returns a string created from one or more code points.

The includes() method of strings returns whether a search string appears within the string.

The String.raw() static method interpolates template literal substitutions, but ignores escape sequences. It is the tag function for template literals.

The repeat() method of strings returns the original string repeated a number of times.

The startsWith() and endsWith() methods of strings returns whether a search string appears at the beginning or end of the provided string.

The @supports at-rule applies styles based on a browser's support for CSS features, such as a CSS property and value. Also known as feature queries.

A Symbol value is a unique, non-enumerable primitive value used for encapsulation or information hiding. For example, a symbol can be a key of an object that can never collide with any other key.

The transform CSS property and its 2D transform functions allow rotating, scaling, skewing, and translating an element. Arbitrary 2D transforms are also possible using a transformation matrix.

The transition shorthand CSS property sets how changes to an element's styles may occur over time. Transitions can be applied to specific CSS properties, all properties, or none.

Unicode point escapes (\\u{}) represent Unicode characters within strings.

A WeakSet object stores unique values of any type without creating strong references to the values, such that membership in the set does not prevent garbage collection of the value.

The word-break CSS property sets how lines break within words.

Channel messaging communicates one-to-one between browsing contexts on the same origin, such as between <iframe> elements or two documents using a shared worker.

The performance global object and the PerformanceObserver API provide access to performance-related information for the current execution context.

The <a> element creates a hyperlink to any resource that's accessible via a URL, such as web pages, files, email addresses, or locations within the same page.

The <abbr> HTML element represents an abbreviation or acronym.

The position: absolute CSS declaration removes an element from the normal flow and positions it relative to its containing block, which is often the root element, or closest positioned ancestor.

The accesskey global HTML attribute gives a hint for generating a keyboard shortcut for the current element. The attribute value must consist of a single printable character.

The <address> element represents contact information for a person or people, or for an organization.

The window.alert(), window.confirm(), and window.prompt() methods open modal dialogs for notifying the user, asking for confirmation, or entering text.

Arrays are ordered lists of JavaScript values.

The Array.isArray() static method checks whether a value is an array.

Array iteration methods

The array splice() method changes an array in-place. You can use it to delete items, overwrite items, or insert items, starting from an index.

The <article> element represents self-contained content, which is intended to be independently distributable or reusable, such as a comment, a blog post, or news article.

The <aside> element represents a portion of a document whose content is only indirectly related to the document's main content.

The attr() CSS function, in content property declarations, sets a ::before or ::after pseudo-element's content to the value of the specified HTML attribute.

The <audio> element plays sound such as audio effects or music, optionally with controls provided by the browser.

The autofocus HTML attribute gives focus to an element on page load.

The <b> HTML element draws reader's attention to text, styling text as bold by default.

The background CSS property is a shorthand that sets several background properties at once.

The background-clip CSS property sets the extent of the background: the padding box, the content box, or the default border box.

The background-color CSS property sets the fill color of an element, behind any content and background images or gradients.

The background-image CSS property sets the graphics to display behind the content of an element and in front of the background color. Graphics may be any combination of images or gradients.

The background-origin CSS property sets the background starting position relative to the border and padding of an element.

The background-position CSS property offsets the initial position of background images relative to the background origin.

The background-size CSS property scales or stretches a background based on the size of the element (with the contain and cover keywords), a length, or percentage.

The visible property of the window.locationbar, window.menubar, window.personalbar, window.scrollbars, window.statusbar, and window.toolbar APIs historically represented the visibility of a browser user interface. For privacy reasons, it now represents whether the window is a pop-up.

The <base> element sets the base URL (the URL that relative URLs are relative to) for all relative URLs in the document.

The <bdo> element overrides the directionality of text, so that the text within is rendered in a different direction than the surrounding text.

The ::before and ::after CSS pseudo-elements select inline boxes preceding and following an element. They are often used with the content property to generate cosmetic content.

The <blockquote> element represents an extended quotation, styling contents as an indented block by default.

The BMP image format is an uncompressed raster graphics file format. Also known as a bitmap.

The <body> element represents the content of an HTML document.

The border-radius CSS property rounds the corners of the border drawn around an element.

The border CSS property sets the color, style, and width of the line around an element.

The box-shadow CSS property applies shadow effects around an element's frame. This can create drop shadow and inner shadow effects.

The box-sizing CSS property sets whether an element's width and height are calculated based on the content-box, which does not count the size of borders or padding, or border-box, which does count them.

The <br> element produces line breaks in text.

The <button> HTML element represents a button that triggers some action, such as submitting a form or opening a dialog, styled as a labeled rectangular box by default.

The calc() CSS function computes mathematical expressions such a calc(100%/3 - 1em).

The <canvas> HTML element is a space to draw graphics in, using the 2D canvas API, WebGL, or WebGPU.

The CanvasRenderingContext2D API is the "2d" rendering context for the <canvas> element. It represents a flat, two-dimensional space for drawing graphics and animations.

The ch CSS length unit is a font-relative length based on the width of the zero (0) character.

The change event for <input>, <select>, and <textarea> elements fires when the user modifies the element's value. Unlike the input event, the change event does not necessarily fire on every alteration to an element's value.

The @charset CSS at-rule specifies the character encoding of an external style sheet.

The <cite> element represents the title of a quoted, referenced, or mentioned creative work, such as a film or book.

The <code> element displays its contents as a fragment of computer code.

The color CSS property sets the primary foreground color of an element, which is used for text, the default border color, and text decorations.

The console API logs debugging messages to the browser development tools' console.

The content CSS property sets the content inside of an element or pseudo-element, replacing the current value. It's often used with the ::before and ::after pseudo-elements to generate cosmetic content.

The contenteditable global HTML attribute allows the user to edit the content of an element, such as inserting or deleting text.

The Set-Cookie HTTP header stores limited amounts of data that persist across request and response, creating shared state between the browser and server.

Cross-Origin Resource Sharing is an HTTP-header based mechanism that allows a server to indicate any origins (domain, scheme, or port) other than its own from which a browser should permit loading resources. Also known as CORS.

The counter-reset and counter-increment CSS properties and the counter() and counters() functions automatically number headings or ordered list items.

The cubic-bezier() CSS easing function interpolates along a smooth curve, creating animations and transitions with continuous changes in speed. The ease, ease-in, ease-out, and ease-in-out keyword values are presets for common Bézier curves.

The currentColor CSS value allows you to reuse an element's computed text color for other properties.

Data URLs are URLs that start with the data: scheme and which directly contain data rather than point to remote resources.

The dataset API attaches and accesses custom data on elements, using either the dataset property of HTMLElement or attributes prefixed with data-.

The Date object represents a single moment in time.

The Worker() constructor runs a script in its own thread, which can send and receive messages with the script that created it. Also known as web workers.

The <del> element represents a range of text that has been deleted from a document, styling text as strikethrough by default.

The <dl>, <dt>, and <dd> HTML elements represent a list of terms and their associated descriptions. Use a description list to create glossaries or similar list of key-value pairs.

The <dfn> element marks a term to be defined, styling text as italic by default.

The display CSS property sets the display behavior of an element's box within its layout and sets the layout behavior for its child elements.

The display: list-item CSS declaration renders an element with the box layout of a <li> HTML element.

The display: table CSS declaration renders an element with the box layout of a <table> HTML element. Child elements may use equivalents to <table> internal elements such as display: table-row for <tr>.

The <div> HTML element is the generic container for content.

The DOM (Document Object Model) API represents HTML and XML documents as trees of nodes. You can use the API to inspect and modify the structure and content of a document.

The Drag and Drop API lets users drag and drop elements and external files such as images onto web pages. Developers can customize which elements can become draggable, the type of feedback the draggable elements produce, and the droppable elements.

The <em> HTML element emphasizes or stresses the content, styling text as italic by default.

The em CSS length unit is a font-relative length equal to the specified font size. In an element with a 2 inch font, 1em equals 2 inches.

The :empty CSS pseudo-class matches elements without child elements.

The Event API and the addEventListener() method on objects that receive events (event targets) represent and handle significant things happening on a page. Many APIs fire events for a wide range of situations relating to those APIs, such as an image loading, a user clicking, or a value changing.

The ex CSS length unit is a font-relative length equal to the used x-height of the first available font. X-height is often equal to the height of the lowercase x.

The <fieldset> and <legend> elements group several form control elements within a web form.

The <figure> and <figcaption> HTML elements represent an illustration, diagram, text, or other self-contained reference content, with an optional caption.

The ::first-letter CSS pseudo-element selects the first letter in an element for styling.

The ::first-line CSS pseudo-element selects the first line of text in an element for styling.

The position: fixed CSS declaration removes an element from the normal flow and positions it relative to the viewport or page.

The float CSS property aligns an element to either side of its container, allowing text and inline elements to flow around it. The clear CSS property sets whether an element is moved below floating elements that proceed it.

Focus events, such as focus and blur, fire when an element gets or loses focus.

The font-family CSS property sets the desired font face for text, along with optional fallback font faces.

The font CSS property shorthand sets multiple font properties, including style, weight, size, and font family.

The font-size CSS property sets the text height.

The font-style CSS property sets the text style, with normal, italic, and oblique options.

The font-variant CSS property is a shorthand for font-variant-alternates, font-variant-caps, font-variant-east-asian, font-variant-emoji, font-variant-ligatures, font-variant-numeric, and font-variant-position.

The font-weight CSS property controls the thickness of a font. It is set explicitly with the keyword bold or a number, or relative to the inherited thickness with the keywords bolder or lighter.

The <form> element contains interactive controls for submitting information.

The form validity CSS pseudo-classes match <form> elements based on the constraints of a form field, such as validity (:valid, :invalid, :in-range, :out-of-range) and necessity (:optional or :required).

Functions are series of statements that can be called and return a value. The function keyword (as in function () { }) and arrow (=>) expression create functions. The JavaScript functions protocol includes default and rest parameters and binding to this.

The navigator.geolocation API requests the user's latitude, longitude, heading, and speed.

The getComputedStyle() global method returns an CSSStyleDeclaration object that represents all CSS declarations applied to a given element.

The GIF (Graphics Interchange Format) image format is a raster graphics file format with animation and lossless compression.

The linear-gradient() and radial-gradient() CSS functions and their repeating counterparts create backgrounds that progress smoothly between multiple colors.

The hashchange event fires when the URL fragment identifier (the part of the URL starting with #) of the current page has changed.

The <head> element contains machine-readable information (metadata) about the document, such as the title, <script> and <style> elements, and <meta> elements.

The <header> and <footer> HTML elements represent content that precedes and follows the main page content, respectively.

The <h1> through <h6> HTML elements represent six levels of section headings, in order of decreasing importance.

The <hgroup> element represents a heading and related content.

The window.history API manipulates the browser session history, from navigations to state management, in the tab or frame that the current page is loaded in.

The <hr> element represents a thematic break between paragraphs, often shown as a horizontal rule.

The Strict-Transport-Security HTTP response header informs browsers that the site should only be accessed using HTTPS, and that any future attempts to access it using HTTP should automatically be converted to HTTPS. Also known as HSTS.

The <html> element represents the top-level of an HTML document and is referred to as the root element.

The Authorization and WWW-Authenticate headers authenticate a user with a server.

HTTP/1.1 is a network protocol used by browsers and servers. It has been superseded by HTTP/2 and HTTP/3.

The <i> HTML element identifies idiomatic content, styling text as italic by default.

The <iframe> element embeds another HTML page into the current page.

The sandbox attribute for the <iframe> HTML element sets many security restrictions on the iframe, such as preventing form submissions or opening modal dialogs. Optional allow- values relax specific restrictions.

The <area> and <map> elements define a clickable area on an image.

The <img> element adds an image into the document.

The @import CSS at-rule loads styles from another stylesheet.

The inherit keyword resets any CSS property to the computed value of that property from the parent element.

The <input type="text"> HTML element allows the user to enter information into a form. By default, an <input> element is a text input.

The <input type="button"> HTML element represents a button that triggers some action, such as submitting a form or opening a dialog, styled as a labeled rectangular box by default. Not to be confused with the <button> element, which contains HTML content.

The <input type="checkbox"> HTML element represents a tickable box with two states, checked and unchecked.

The <input type="email">, <input type="tel">, and <input type="url"> HTML elements represent email address, telephone number, and URL fields in a form.

The <input type="file"> HTML element shows a file picker from which users can choose a file to upload with the form.

The <input type="file" multiple> HTML element shows a file picker from which users can choose one or more files to upload with a form.

The <input type="hidden"> HTML element represents a form field that is not shown visually but is still included in the form submission.

The <input type="image"> HTML element is an image that can be used to submit a form, like the <input type="submit"> element.

The <input type="number"> HTML element represents numeric input data.

The <input type="password"> HTML element represents a field for users to enter a password. The password is hidden from view, typically replaced by dots or asterisks.

The <input type="radio"> HTML element represents one button in a group such that only one can be chosen at a time.

The <input type="reset"> HTML element represents a button that sets all form fields to their initial values.

The :checked, :disabled, and :enabled CSS pseudo-classes match form elements based on their state.

The <input type="submit"> HTML element represents a button that triggers an action on its associated <form>, such as sending the form data to a server.

The <ins> element represents a range of text that has been inserted into a document, styling text as underlined by default.

The for...of loop operates on a sequence of values sourced from an iterable object, such as arrays, array-like objects, DOM collections, iterators, generators, and user-defined iterables. All built-in iterators inherit from the Iterator class.

JavaScript is a programming language that runs in browsers, usually through the <script> element. JavaScript has changed over many years. This feature represents the oldest language features, such as built-in objects, statements, and operators. Also known as ECMAScript.

The JPEG image format is a raster graphics file format with lossy compression.

The JSON API provides static methods for parsing values from and converting values to JavaScript Object Notation (JSON), a serialization format for objects, arrays, numbers, strings, Boolean values, and null.

The <kbd> element represents textual user input, such as keyboard or voice input, styling text in monospaced type by default.

The keydown and keyup events fire for each key press (or, with modifier keys, a combination of key presses) on a keyboard.

The <label> HTML element represents a caption for a form field.

The :lang() CSS functional pseudo-class matches elements based on their content language.

The lang global HTML attribute defines the language of an element. It's used by assistive technology to correctly read the content, translation tools to select the origin language, and other applications.

The navigator.language property is a string representing the preferred language of the user, usually the language of the browser UI. The navigator.languages property is an array of strings representing the user's preferred languages.

The letter-spacing CSS property controls the amount of space between each letter in an element or block of text.

The line-height CSS property sets the spacing between text baselines, oriented to the horizontal or vertical writing mode.

The <p> element represents a paragraph of text.

The padding CSS property sets space between an element's edge and its contents. It is a shorthand for padding-top, padding-right, padding-bottom, and padding-left.

The pageshow and pagehide transition events fire when a document loads or unloads due to a navigation, such as clicking on a link on a page or the back button in a browser.

The document.visibilityState and document.hidden properties tell you whether the page is visible to the user (for example, it's not minimized or in a background tab).

The physical CSS properties, top, right, bottom, and left, set the inset position of an element relative to the corresponding side of a container determined by the element's position property.

The pointer-events CSS property sets whether a user can interact with an element using a mouse, touch, or other pointing input device.

The position CSS property sets the origin position of an element to an element, the element's scrollport, or the viewport.

The postMessage() global method sends cross-origin messages to windows and workers, including popups and iframes. Also known as cross-document messaging.

The <pre> element represents a block element of preformatted text that is presented exactly as written, including all white space.

The <progress> element displays an indicator showing the completion progress of a task, typically displayed as a progress bar.

A promise represents an asynchronous operation which eventually succeeds or fails.

The <q> element represents a short inline quotation.

The RegExp object represents a regular expression, a notation for matching text patterns.

The position: relative CSS declaration offsets the position of an element relative to its position in the normal flow.

The rem CSS length unit is a font-relative length that is equal to the font size of the root HTML element which for most browsers is 16px.

The requestAnimationFrame() method schedules a function that runs before the next repaint. You can use it to animate content with JavaScript.

The :root pseudo-class matches the root element of the document, usually the <html> element.

The <ruby> element produces small annotations that are rendered with its base text.

The <s> HTML element indicates text that is no longer relevant or accurate, styling text as strikethrough by default.

The <samp> element represents a sample or quoted output from a computer program. Styled in a monospace font by default.

The window.screen property contains information about the screen of the output device that the referenced window is being rendered on.

The <script> element contains or loads data or executable code. This is typically used to load JavaScript code. The <noscript> element represents alternative content to show when scripting is not allowed.

The <input type="search"> HTML element represents a text field for search queries.

The <section> element is a generic standalone section of a document, which doesn't have a more specific semantic element to represent it.

The <select> element provides a menu of options for a user to pick from, typically rendered as a dropdown list.

CSS selectors match elements based on their type, attributes, and relationship to other elements. They define the specific elements to which a block of styles will be applied. This feature represents the oldest selectors of CSS.

Set objects store unique values of any type.

The setInterval() global function repeatedly executes provided code on a given delay, and the accompanying clearInterval() cancels the interval.

The setTimeout() global function executes provided code after a given duration of time, and the accompanying clearTimeout() cancels the timer.

The <small> element represents side-comments and small print, like copyright and legal text, independent of its styled presentation. Styled in a reduced font size by default.

The <source> element sets a media resource for the <picture>, <video>, and <audio> elements.

The <span> HTML element is the generic inline container for content.

The position: static CSS declaration positions an element in the normal flow. A statically positioned element ignores physical and logical properties such as top or inset-block-start.

The string type (and String object) represents a sequence of characters.

The <strong> HTML element brings attention to the content, styling text as bold by default.

The <style> element embeds an inline CSS stylesheet in a document.

The style global HTML attribute applies inline CSS styling declarations to individual elements.

The <sub> and <sup> elements sets inline text to be displayed as subscript or superscript for solely typographical reasons.

The <filter> SVG element applies custom effects such as color manipulation, blurring, or morphing to SVG elements.

The system color CSS keywords, such as ButtonBorder or LinkText, allow you to match default colors from the user agent.

The <table> HTML element, with several related elements, represents tabular data in rows and columns of cells.

The :target CSS pseudo-class matches the element with an ID matching the URL fragment.

The text-align CSS property sets the horizontal placement of the inner content of a block element.

The text-decoration CSS property sets the style and color of decorative lines including underline, overline, line-through, or a combination of lines.

The text-indent CSS property sets the size of the empty space (indentation) at the beginning of lines in a text.

The text-overflow CSS property sets how hidden overflow content appears to users. The property can clip content, truncate content with an ellipsis (…), or truncate with a custom string.

The text-shadow CSS property sets the position and styles of shadow on text.

The <track> element is used as a child of the media elements that lets you specify a timed text track to be displayed in parallel with the media element.

The text-transform CSS property sets text case and capitalization.

The <textarea> element represents an editing control that allows users to enter multi-line, free-form, plain text.

The <title> element sets the title of the document and exposes it to users via the UI of the browser or app they're using and through assistive technology.

The title global HTML attribute sets information about an element, such as a name or description. The value is typically shown as a tooltip that appears on mouse over. Since it's not often available to touch-only, keyboard-only, or assistive technology users, it's not a substitute for other text.

Typed arrays are ordered lists of JavaScript values, where all values are of the same numerical type, such as 8-bit integers or 32-bit floating point numbers.

The <u> HTML element makes non-textual annotations, styling text as underlined by default.

A URL object represents a web address, like https://example.com/, and parts of the address, such as the domain, path, and query string (as URLSearchParams).

The :active, :focus, and :hover CSS pseudo-classes match elements based on how users are interacting with them.

The <var> element represents the name of a variable in a mathematical expression or a programming context.

The vertical-align CSS property sets the vertical alignment of inline, inline-block, and table cell elements. It has no effect on block-level elements.

The <video> element plays videos or movies, optionally with controls provided by the browser.

The visibility CSS property sets whether an element is shown. Invisible elements still affect the document layout.

The <wbr> HTML element represents a word break opportunity, to explicitly mark a place within a word where a line might be broken.

A WeakMap object holds key-value pairs that do not create strong references to its keys, such that value data can be associated with a key without preventing garbage collection of the key.

The Web Cryptography API performs low-level cryptographic operations, such as encryption, decryption, and signature verification. Also known as the Web Crypto API.

The WebGLRenderingContext API is the "webgl" rendering context for the <canvas> element. It represents a space for drawing two- and three-dimensional graphics and animations.

The WEBGL_depth_texture extension for WebGL 1.0 contexts defines 2D depth and depth-stencil textures.

The WebSocket API opens a two-way communication channel between the user's browser and a server.

WebVTT is a captions and subtitles format. WebVTT files are loaded using the <track> element, and the VTTCue API can be used to create or update cues dynamically.

The white-space CSS property sets how white space is collapsed and how lines wrap. It is a shorthand for white-space-collapse and text-wrap-mode.

The width and height CSS properties set the preferred physical size of an element.

The window global object represents a browser tab or iframe and its relationship to the document and other tabs. It's also a generic global object, under which many other APIs are located.

The word-spacing CSS property sets the amount of white space between words.

The XMLHttpRequest API makes HTTP requests. It's the predecessor to fetch(). Also known as XHR.

The XMLSerializer API provides the serializeToString() method to construct an XML string representing a DOM tree.

The document.evaluate() method selects elements in an HTML or XML document based on an expression of XPath, a domain specific language for querying XML documents. Also known as XML Path Language.

The XSLTProcessor API transforms XML documents into new XML or HTML documents, using XSLT stylesheets. You can use XSLT to convert data between different XML schemas or to convert XML data into web pages or PDF documents. Also known as Extensible Stylesheet Language Transformations.

The z-index CSS property orders overlapping elements, with higher values appearing in front of or on top of lower values.