HTML: The Living Standard

This specification relies on several other underlying specifications.

Infra

The following terms are defined in the WHATWG Infra standard: [INFRA]

• The general iteration terms while, continue, and break.
• code point and its synonym character
• surrogate
• scalar value
• noncharacter
• JavaScript string, code unit, and JavaScript string length
• scalar value string
• string length
• ASCII whitespace
• control
• ASCII digit
• ASCII upper hex digit
• ASCII lower hex digit
• ASCII hex digit
• ASCII upper alpha
• ASCII lower alpha
• ASCII alpha
• ASCII alphanumeric
• ASCII lowercase
• ASCII uppercase
• ASCII case-insensitive
• strip newlines
• strip leading and trailing ASCII whitespace
• strip and collapse ASCII whitespace
• split a string on ASCII whitespace
• split a string on commas
• collect a sequence of code points and its associated position variable
• skip ASCII whitespace
• The ordered map data structure and the associated definitions for exists, getting the value of an entry, and setting the value of an entry
• The list data structure and the associated definitions for append, replace, remove, empty, contains, size, is empty, and iterate
• The stack data structure and the associated definitions for push and pop
• The ordered set data structure and the associated definition for append
• The struct specification type and the associated definition for item
• The forgiving-base64 encode and forgiving-base64 decode algorithms
• HTML namespace
• MathML namespace
• SVG namespace
• XLink namespace
• XML namespace
• XMLNS namespace

Unicode and Encoding

The Unicode character set is used to represent textual data, and the WHATWG Encoding standard defines requirements around character encodings. [UNICODE]

This specification introduces terminology based on the terms defined in those specifications, as described earlier.

The following terms are used as defined in the WHATWG Encoding standard: [ENCODING]

• Getting an encoding
• Get an output encoding
• The generic decode algorithm which takes a byte stream and an encoding and returns a character stream
• The UTF-8 decode algorithm which takes a byte stream and returns a character stream, additionally stripping one leading UTF-8 Byte Order Mark (BOM), if any
• The UTF-8 decode without BOM algorithm which is identical to UTF-8 decode except that it does not strip one leading UTF-8 Byte Order Mark (BOM)
• The UTF-8 decode without BOM or fail algorithm which is identical to UTF-8 decode without BOM except that it returns failure upon encountering an error
• The encode algorithm which takes a character stream and an encoding and returns a byte stream
• The UTF-8 encode algorithm which takes a character stream and returns a byte stream

XML and related specifications

Implementations that support the XML syntax for HTML must support some version of XML, as well as its corresponding namespaces specification, because that syntax uses an XML serialization with namespaces. [XML] [XMLNS]

Data mining tools and other user agents that perform operations on content without running scripts, evaluating CSS or XPath expressions, or otherwise exposing the resulting DOM to arbitrary content, may "support namespaces" by just asserting that their DOM node analogues are in certain namespaces, without actually exposing the namespace strings.

In the HTML syntax, namespace prefixes and namespace declarations do not have the same effect as in XML. For instance, the colon has no special meaning in HTML element names.

---

The attribute with the tag name xml:space in the XML namespace is defined by the XML specification. [XML]

The Name production is defined in the XML specification. [XML]

This specification also references the <?xml-stylesheet?> processing instruction, defined in the Associating Style Sheets with XML documents specification. [XMLSSPI]

This specification also non-normatively mentions the XSLTProcessor interface and its transformToFragment() and transformToDocument() methods. [XSLTP]

URLs

The following terms are defined in the WHATWG URL standard: [URL]

• host
• domain
• IPv4 address
• IPv6 address
• URL
• Origin of URLs
• Absolute URL
• Relative URL
• The URL parser and basic URL parser as well as these parser states:
  • scheme start state
  • host state
  • hostname state
  • port state
  • path start state
  • query state
  • fragment state
• URL record, as well as its individual components:
  • scheme
  • username
  • password
  • host
  • port
  • path
  • query
  • fragment
  • cannot-be-a-base-URL flag
  • object
• valid URL string
• The cannot have a username/password/port concept
• The URL serializer
• The host parser
• The host serializer
• Host equals
• URL equals
• serialize an integer
• Default encode set
• UTF-8 percent encode
• Percent decode
• set the username
• set the password
• The application/x-www-form-urlencoded format
• The application/x-www-form-urlencoded serializer

A number of schemes and protocols are referenced by this specification also:

• The about: scheme [ABOUT]
• The blob: scheme [FILEAPI]
• The data: scheme [RFC2397]
• The http: scheme [HTTP]
• The https: scheme [HTTP]
• The mailto: scheme [MAILTO]
• The sms: scheme [SMS]
• The urn: scheme [URN]

Media fragment syntax is defined in the Media Fragments URI specification. [MEDIAFRAG]

HTTP and related specifications

The following terms are defined in the HTTP specifications: [HTTP]

• `Accept` header
• `Accept-Language` header
• `Cache-Control` header
• `Content-Disposition` header
• `Content-Language` header
• `Last-Modified` header
• `Referer` header

The following terms are defined in the Cookie specification: [COOKIES]

• cookie-string
• receives a set-cookie-string
• `Cookie` header

The following term is defined in the Web Linking specification: [WEBLINK]

• `Link` header

The following terms are defined in the WHATWG MIME Sniffing standard: [MIMESNIFF]

• MIME type
• valid MIME type
• valid MIME type with no parameters
• XML MIME type
• HTML MIME type

Fetch

The following terms are defined in the WHATWG Fetch standard: [FETCH]

• about:blank
• An HTTP(S) scheme
• A network scheme
• A fetch scheme
• HTTPS state value
• CORS protocol
• default `User-Agent` value
• extract a MIME type
• fetch
• HTTP-redirect fetch
• ok status
• navigation request
• network error
• `Origin` header
• process response
• set
• terminate
• the RequestCredentials enumeration
• the RequestDestination enumeration
• response and its associated:
  • type
  • url
  • url list
  • status
  • header list
  • body
  • internal response
  • CSP list
  • HTTPS state
  • location URL
• request and its associated:
  • url
  • method
  • header list
  • body
  • client
  • reserved client
  • target client id
  • initiator
  • destination
  • potential destination
  • translating a potential destination
  • priority
  • origin
  • referrer
  • synchronous flag
  • mode
  • credentials mode
  • use-URL-credentials flag
  • unsafe-request flag
  • cache mode
  • redirect mode
  • referrer policy
  • cryptographic nonce metadata
  • integrity metadata
  • parser metadata

The following terms are defined in Referrer Policy: [REFERRERPOLICY]

• referrer policy
• The `Referrer-Policy` HTTP header
• The parse a referrer policy from a `Referrer-Policy` header algorithm
• The "no-referrer", "no-referrer-when-downgrade", "no-referrer-when-downgrade", and "unsafe-url" referrer policies

The following terms are defined in Mixed Content: [MIX]

• a priori authenticated URL

Web IDL

The IDL fragments in this specification must be interpreted as required for conforming IDL fragments, as described in the Web IDL specification. [WEBIDL]

The following terms are defined in the Web IDL specification:

• extended attribute
• named constructor
• array index property name
• supported property indices
• determine the value of an indexed property
• set the value of an existing indexed property
• set the value of a new indexed property
• support named properties
• supported property names
• determine the value of a named property
• set the value of an existing named property
• set the value of a new named property
• delete an existing named property
• perform a security check
• platform object
• primary interface
• interface object
• interface prototype object
• global environment associated with a platform object
• callback context
• frozen array and creating a frozen array
• callback this value
• converting between Web IDL types and JS types
• invoking and constructing callback functions
• converting to a sequence of Unicode scalar values

The Web IDL specification also defines the following types that are used in Web IDL fragments in this specification:

• ArrayBuffer
• ArrayBufferView
• boolean
• DOMString
• double
• enumeration
• Error
• Function
• long
• object
• RegExp
• Uint8ClampedArray
• unrestricted double
• unsigned long
• USVString

The term throw in this specification is used as defined in the Web IDL specification. The DOMException type and the following exception names are defined by Web IDL and used by this specification:

• "IndexSizeError"
• "HierarchyRequestError"
• "InvalidCharacterError"
• "NotFoundError"
• "NotSupportedError"
• "InvalidStateError"
• "SyntaxError"
• "InvalidAccessError"
• "SecurityError"
• "NetworkError"
• "AbortError"
• "QuotaExceededError"
• "DataCloneError"
• "EncodingError"
• "NotAllowedError"

When this specification requires a user agent to create a Date object representing a particular time (which could be the special value Not-a-Number), the milliseconds component of that time, if any, must be truncated to an integer, and the time value of the newly created Date object must represent the resulting truncated time.

For instance, given the time 23045 millionths of a second after 01:00 UTC on January 1st 2000, i.e. the time 2000-01-01T00:00:00.023045Z, then the Date object created representing that time would represent the same time as that created representing the time 2000-01-01T00:00:00.023Z, 45 millionths earlier. If the given time is NaN, then the result is a Date object that represents a time value NaN (indicating that the object does not represent a specific instant of time).

JavaScript

Some parts of the language described by this specification only support JavaScript as the underlying scripting language. [JAVASCRIPT]

Users agents that support JavaScript must also implement the ECMAScript Internationalization API Specification. [JSINTL]

The term "JavaScript" is used to refer to ECMA-262, rather than the official term ECMAScript, since the term JavaScript is more widely known. Similarly, the MIME type used to refer to JavaScript in this specification is text/javascript, since that is the most commonly used type, despite it being an officially obsoleted type according to RFC 4329. [RFC4329]

The following terms are defined in the JavaScript specification and used in this specification:

• active function object
• agent and agent cluster
• automatic semicolon insertion
• The current Realm Record
• early error
• Directive Prologue
• invariants of the essential internal methods
• JavaScript execution context
• JavaScript execution context stack
• JavaScript realm
• running JavaScript execution context
• Use Strict Directive
• Well-Known Symbols, including @@hasInstance, @@isConcatSpreadable, @@toPrimitive, and @@toStringTag
• Well-Known Intrinsic Objects, including %ArrayBuffer%, %ArrayPrototype%, and %ObjProto_valueOf%
• The FunctionBody production
• The Module production
• The Pattern production
• The Script production
• The Type notation
• The List and Record specification types
• The Property Descriptor specification type
• The Script Record specification type
• The Source Text Module Record specification type and its Evaluate and Instantiate methods
• The ArrayCreate abstract operation
• The Call abstract operation
• The Construct abstract operation
• The CopyDataBlockBytes abstract operation
• The CreateByteDataBlock abstract operation
• The CreateDataProperty abstract operation
• The DetachArrayBuffer abstract operation
• The EnqueueJob abstract operation
• The EnumerableOwnProperties abstract operation
• The FunctionCreate abstract operation
• The Get abstract operation
• The GetFunctionRealm abstract operation
• The HasOwnProperty abstract operation
• The HostEnsureCanCompileStrings abstract operation
• The HostPromiseRejectionTracker abstract operation
• The HostResolveImportedModule abstract operation
• The InitializeHostDefinedRealm abstract operation
• The IsAccessorDescriptor abstract operation
• The IsCallable abstract operation
• The IsConstructor abstract operation
• The IsDataDescriptor abstract operation
• The IsDetachedBuffer abstract operation
• The IsSharedArrayBuffer abstract operation
• The NewObjectEnvironment abstract operation
• The OrdinaryGetPrototypeOf abstract operation
• The OrdinarySetPrototypeOf abstract operation
• The OrdinaryIsExtensible abstract operation
• The OrdinaryPreventExtensions abstract operation
• The OrdinaryGetOwnProperty abstract operation
• The OrdinaryDefineOwnProperty abstract operation
• The OrdinaryGet abstract operation
• The OrdinarySet abstract operation
• The OrdinaryDelete abstract operation
• The OrdinaryOwnPropertyKeys abstract operation
• The ParseModule abstract operation
• The ParseScript abstract operation
• The RunJobs abstract operation
• The SameValue abstract operation
• The ScriptEvaluation abstract operation
• The SetImmutablePrototype abstract operation
• The ToBoolean abstract operation
• The ToString abstract operation
• The ToUint32 abstract operation
• The TypedArrayCreate abstract operation
• The Abstract Equality Comparison algorithm
• The Strict Equality Comparison algorithm
• The Date class
• The SharedArrayBuffer class
• The TypeError class
• The RangeError class
• The typeof operator
• The TypedArray Constructors table

DOM

The Document Object Model (DOM) is a representation — a model — of a document and its content. The DOM is not just an API; the conformance criteria of HTML implementations are defined, in this specification, in terms of operations on the DOM. [DOM]

Implementations must support DOM and the events defined in UI Events, because this specification is defined in terms of the DOM, and some of the features are defined as extensions to the DOM interfaces. [DOM] [UIEVENTS]

In particular, the following features are defined in the WHATWG DOM standard: [DOM]

• Attr interface
• Comment interface
• DOMImplementation interface
• Document interface
• DocumentFragment interface
• DocumentType interface
• ChildNode interface
• Element interface
• Node interface
• NodeList interface
• ProcessingInstruction interface
• ShadowRoot interface
• Text interface
• node document concept
• host concept
• shadow root concept
• HTMLCollection interface
• HTMLCollection.length attribute
• HTMLCollection.item() method
• HTMLCollection.namedItem() method
• The terms collection and represented by the collection
• DOMTokenList interface
• DOMTokenList.value attribute
• createDocument() method
• createHTMLDocument() method
• createElement() method
• createElementNS() method
• getElementById() method
• getElementsByClassName() method
• appendChild() method
• cloneNode() method
• importNode() method
• preventDefault() method
• id attribute
• textContent attribute
• The tree and shadow tree concepts
• The tree order and shadow-including tree order concepts
• The child concept
• The root and shadow-including root concepts
• The inclusive ancestor and shadow-including descendant concepts
• The first child and next sibling concepts
• The document element concept
• The in a document tree, in a document (legacy), and connected concepts
• The slot concept, and its name and assigned nodes
• The find flattened slotables algorithm
• The assign a slot algorithm
• The pre-insert, insert, append, replace, replace all, remove, and adopt algorithms for nodes
• The change, append, remove, replace, and set value algorithms for attributes
• The insertion steps, removing steps, adopting steps, and child text content change steps hooks
• The attribute list concept
• The data of a text node
• The child text content of a node
• Event interface
• EventTarget interface
• The activation behavior hook
• The legacy-pre-activation behavior hook
• The legacy-canceled-activation behavior hook
• The create an event algorithm
• The fire an event algorithm
• The canceled flag
• The dispatch algorithm
• EventInit dictionary type
• type attribute
• target attribute
• currentTarget attribute
• bubbles attribute
• cancelable attribute
• composed flag
• isTrusted attribute
• initEvent() method
• addEventListener() method
• EventListener callback interface
• The type of an event
• The concept of an event listener and the event listeners associated with an EventTarget
• The encoding (herein the character encoding) and content type of a Document
• The distinction between XML documents and HTML documents
• The terms quirks mode, limited-quirks mode, and no-quirks mode
• The algorithm to clone a Node, and the concept of cloning steps used by that algorithm
• The concept of base URL change steps and the definition of what happens when an element is affected by a base URL change
• The concept of an element's unique identifier (ID)
• The concept of an element's classes
• The term supported tokens
• The concept of a DOM range, and the terms start, end, and boundary point as applied to ranges.
• The create an element algorithm
• The element interface concept
• The concepts of custom element state, and of defined and custom elements
• An element's custom element definition
• An element's is value
• MutationObserver interface and mutation observers in general

The following features are defined in the UI Events specification: [UIEVENTS]

• The MouseEvent interface
• The MouseEvent interface's relatedTarget attribute
• MouseEventInit dictionary type
• The FocusEvent interface
• The FocusEvent interface's relatedTarget attribute
• The UIEvent interface
• The UIEvent interface's view attribute
• auxclick event
• click event
• dblclick event
• mousedown event
• mouseenter event
• mouseleave event
• mousemove event
• mouseout event
• mouseover event
• mouseup event
• wheel event
• keydown event
• keypress event
• keyup event

The following features are defined in the Touch Events specification: [TOUCH]

• Touch interface
• Touch point concept
• touchend event

The following features are defined in the Pointer Events specification: [POINTEREVENTS]

• pointerup event

This specification sometimes uses the term name to refer to the event's type; as in, "an event named click" or "if the event name is keypress". The terms "name" and "type" for events are synonymous.

The following features are defined in the DOM Parsing and Serialization specification: [DOMPARSING]

• DOMParser
• innerHTML
• outerHTML

The Selection interface is defined in the Selection API specification. [SELECTION]

User agents are encouraged to implement the features described in the execCommand specification. [EXECCOMMAND]

The following parts of the WHATWG Fullscreen API standard are referenced from this specification, in part to define the rendering of dialog elements, and also to define how the Fullscreen API interacts with HTML: [FULLSCREEN]

• top layer (an ordered set) and its add operation
• requestFullscreen()
• run the fullscreen steps

The High Resolution Time specification provides the DOMHighResTimeStamp typedef and the Performance interface's now() method. [HRT]

File API

This specification uses the following features defined in the File API specification: [FILEAPI]

• The Blob interface and its type attribute
• The File interface and its name and lastModified attributes
• The FileList interface
• The concept of a Blob's snapshot state
• The concept of read errors
• Blob URL Store

Indexed Database API

This specification uses cleanup Indexed Database transactions defined by the Indexed Database API specification. [INDEXEDDB]

Media Source Extensions

The following terms are defined in the Media Source Extensions specification: [MEDIASOURCE]

• MediaSource interface
• detaching from a media element

Media Capture and Streams

The following terms are defined in the Media Capture and Streams specification: [MEDIASTREAM]

• MediaStream interface
• getUserMedia() method

XMLHttpRequest

This specification references the XMLHttpRequest specification to describe how the two specifications interact and to use its ProgressEvent features. The following features and terms are defined in the XMLHttpRequest specification: [XHR]

• XMLHttpRequest interface
• XMLHttpRequest.responseXML attribute
• ProgressEvent interface
• ProgressEvent.lengthComputable attribute
• ProgressEvent.loaded attribute
• ProgressEvent.total attribute
• Fire a progress event named e

Battery Status

The following features are defined in the Battery Status API specification: [BATTERY]

• getBattery() method

Media Queries

Implementations must support Media Queries. The <media-condition> feature is defined therein. [MQ]

CSS modules

While support for CSS as a whole is not required of implementations of this specification (though it is encouraged, at least for Web browsers), some features are defined in terms of specific CSS requirements.

When this specification requires that something be parsed according to a particular CSS grammar, the relevant algorithm in the CSS Syntax specification must be followed. [CSSSYNTAX]

In particular, some features require that a string be parsed as a CSS <color> value. When parsing a CSS value, user agents are required by the CSS specifications to apply some error handling rules. These apply to this specification also. [CSSCOLOR] [CSS]

For example, user agents are required to close all open constructs upon finding the end of a style sheet unexpectedly. Thus, when parsing the string "rgb(0,0,0" (with a missing close-parenthesis) for a color value, the close parenthesis is implied by this error handling rule, and a value is obtained (the color 'black'). However, the similar construct "rgb(0,0," (with both a missing parenthesis and a missing "blue" value) cannot be parsed, as closing the open construct does not result in a viable value.

The following terms and features are defined in the CSS specification: [CSS]

• viewport
• line box
• out-of-flow
• in-flow
• replaced element
• intrinsic dimensions
• content area
• content box
• border box
• margin box
• border edge
• margin edge
• collapsing margins
• containing block
• inline box
• block box
• The 'margin-top', 'margin-bottom', 'margin-left', and 'margin-right' properties
• The 'padding-top', 'padding-bottom', 'padding-left', and 'padding-right' properties
• The 'top', 'bottom', 'left', and 'right' properties
• The 'float' property
• The 'clear' property
• The 'width' property
• The 'height' property
• The 'line-height' property
• The 'vertical-align' property
• The 'content' property
• The 'inline-block' value of the 'display' property
• The 'visibility' property

The CSS specification also defines the following border properties: [CSS]

Border properties

	Top	Bottom	Left	Right
Width	'border-top-width'	'border-bottom-width'	'border-left-width'	'border-right-width'
Style	'border-top-style'	'border-bottom-style'	'border-left-style'	'border-right-style'
Color	'border-top-color'	'border-bottom-color'	'border-left-color'	'border-right-color'

The terms intrinsic width and intrinsic height refer to the width dimension and the height dimension, respectively, of intrinsic dimensions.

The basic version of the 'display' property is defined in the CSS specification, and the property is extended by other CSS modules. [CSS] [CSSRUBY] [CSSTABLE]

The following terms and features are defined in the CSS Logical Properties specification: [CSSLOGICAL]

• The 'margin-block-start', 'margin-block-end', 'margin-inline-start', and 'margin-inline-end' properties
• The 'padding-block-start', 'padding-block-end', 'padding-inline-start', and 'padding-inline-end' properties

The following terms and features are defined in the CSS Color specification: [CSSCOLOR]

• named color
• <color>
• The 'color' property

The term paint source is used as defined in the CSS Image Values and Replaced Content specification to define the interaction of certain HTML elements with the CSS 'element()' function. [CSSIMAGES]

The term default object size and the 'object-fit' property are also defined in the CSS Image Values and Replaced Content specification. [CSSIMAGES]

The following features are defined in the CSS Backgrounds and Borders specification: [CSSBG]

• The 'background-color' property
• The 'background-image' property
• The <position> CSS data type

The term block-level is defined in the CSS Display specification. [CSSDISPLAY]

The following features are defined in the CSS Fonts specification: [CSSFONTS]

• The 'font-family' property
• The 'font-weight' property
• The 'font-size' property
• The 'font' property

The 'list-style-type' property is defined in the CSS Lists and Counters specification. [CSSLISTS]

The 'overflow' property and its 'hidden' value are defined in the CSS Overflow specification. [CSSOVERFLOW]

The following features are defined in the CSS Positioned Layout specification: [CSSPOSITION]

• The 'position' property and its 'static' value

The 'ruby-base' value of the 'display' property is defined in the CSS Ruby Layout specification. [CSSRUBY]

The following features are defined in the CSS Table specification: [CSSTABLE]

• The 'border-spacing' property
• The 'border-collapse' property
• The 'table-cell', 'table-row', 'table-caption', and 'table' values of the 'display' property

The following features are defined in the CSS Text specification: [CSSTEXT]

• The 'text-transform' property
• The 'white-space' property
• The 'text-align' property
• The 'letter-spacing' property

The following features are defined in the CSS Writing Modes specification: [CSSWM]

• The 'direction' property
• The 'unicode-bidi' property
• The block flow direction, block size, inline size, block-start, block-end, inline-start, inline-end, line-left, and line-right concepts

The following features are defined in the CSS Basic User Interface specification: [CSSUI]

• The 'outline' property
• The 'cursor' property
• The 'appearance' property

Implementations that support scripting must support the CSS Object Model. The following features and terms are defined in the CSSOM specifications: [CSSOM] [CSSOMVIEW]

• Screen interface
• LinkStyle interface
• CSSStyleDeclaration interface
• cssText attribute of CSSStyleDeclaration
• StyleSheet interface
• create a CSS style sheet
• remove a CSS style sheet
• associated CSS style sheet
• CSS style sheets and their properties:
  • type
  • location
  • parent CSS style sheet
  • owner node
  • owner CSS rule
  • media
  • title
  • alternate flag
  • disabled flag
  • CSS rules
  • origin-clean flag
• CSS style sheet set
• CSS style sheet set name
• preferred CSS style sheet set name
• change the preferred CSS style sheet set name
• Serializing a CSS value
• run the resize steps
• run the scroll steps
• evaluate media queries and report changes
• Scroll an element into view
• Scroll to the beginning of the document
• The resize event
• The scroll event
• set up browsing context features

The following features and terms are defined in the CSS Syntax specifications: [CSSSYNTAX]

• Parse a comma-separated list of component values
• component value
• environment encoding
• <whitespace-token>

The following terms are defined in the Selectors specification: [SELECTORS]

• type selector
• attribute selector
• pseudo-class

The following features are defined in the CSS Values and Units specification: [CSSVALUES]

• <length>
• The 'em' unit
• The 'ex' unit
• The 'vw' unit
• The 'in' unit
• The 'px' unit
• The 'attr()' function
• The 'calc()' function

The term style attribute is defined in the CSS Style Attributes specification. [CSSATTR]

The following terms are defined in the CSS Cascading and Inheritance specification: [CSSCASCADE]

• specified value
• computed value
• used value

The CanvasRenderingContext2D object's use of fonts depends on the features described in the CSS Fonts and Font Loading specifications, including in particular FontFace objects and the font source concept. [CSSFONTS] [CSSFONTLOAD]

The following interfaces and terms are defined in the Geometry Interfaces Module specification: [GEOMETRY]

• DOMMatrix interface
• DOMMatrix2DInit and DOMMatrixInit dictionaries
• The create a DOMMatrix from a dictionary algorithm for DOMMatrix2DInit or DOMMatrixInit

Intersection Observer

The following term is defined in the Intersection Observer specification: [INTERSECTIONOBSERVER]

• run the update intersection observations steps

WebGL

The following interface is defined in the WebGL specification: [WEBGL]

• WebGLRenderingContext interface

WebVTT

Implementations may support WebVTT as a text track format for subtitles, captions, chapter titles, metadata, etc, for media resources. [WEBVTT]

The following terms, used in this specification, are defined in the WebVTT specification:

• WebVTT file
• WebVTT file using cue text
• WebVTT file using chapter title text
• WebVTT file using only nested cues
• WebVTT parser
• The rules for updating the display of WebVTT text tracks
• The WebVTT text track cue writing direction
• VTTCue interface

The WebSocket protocol

The following terms are defined in the WHATWG Fetch standard: [FETCH]

• establish a WebSocket connection

The following terms are defined in the WebSocket protocol specification: [WSP]

• the WebSocket connection is established
• extensions in use
• subprotocol in use
• a WebSocket message has been received
• send a WebSocket Message
• fail the WebSocket connection
• close the WebSocket connection
• start the WebSocket closing handshake
• the WebSocket closing handshake is started
• the WebSocket connection is closed (possibly cleanly)
• the WebSocket connection close code
• the WebSocket connection close reason
• Sec-WebSocket-Protocol field

ARIA

The role attribute is defined in the ARIA specification, as are the following roles: [ARIA]

• button
• presentation

In addition, the following aria-* content attributes are defined in the ARIA specification: [ARIA]

• aria-describedby
• aria-disabled
• aria-label

Finally, the following terms are defined in the ARIA specification: [ARIA]

• accessible name

Content Security Policy

The following terms are defined in Content Security Policy: [CSP]

• Content Security Policy
• Content Security Policy directive
• The Content Security Policy syntax
• enforce the policy
• The parse a serialized Content Security Policy algorithm
• The Initialize a global object's CSP list algorithm
• The Initialize a Document's CSP list algorithm
• The Should element's inline behavior be blocked by Content Security Policy? algorithm
• The Should navigation request of type from source in target be blocked by Content Security Policy? algorithm
• The Should navigation response to navigation request of type from source in target be blocked by Content Security Policy? algorithm
• The report-uri directive
• The EnsureCSPDoesNotBlockStringCompilation abstract operation
• The Is base allowed for Document? algorithm
• The frame-ancestors directive
• The sandbox directive
• The Should element be blocked a priori by Content Security Policy? algorithm

Service Workers

The following terms are defined in Service Workers: [SW]

• active worker
• client message queue
• control
• handle fetch
• match service worker registration
• scope url
• script url
• service worker
• service worker client
• service worker registration
• service worker type
• serviceworker link
• ServiceWorker interface
• ServiceWorkerContainer interface
• ServiceWorkerGlobalScope interface
• use cache
• update via cache mode

Secure Contexts

The following terms are defined in Secure Contexts: [SECURE-CONTEXTS]

• Is environment settings object a secure context?
• non-secure context
• secure context

Payment Request API

The following feature is defined in the Payment Request API specification: [PAYMENTREQUEST]

• PaymentRequest interface

MathML

While support for MathML as a whole is not required by this specification (though it is encouraged, at least for Web browsers), certain features depend upon small parts of MathML being implemented. [MATHML]

The following features are defined in the MathML specification:

• MathML annotation-xml element
• MathML math element
• MathML merror element
• MathML mi element
• MathML mn element
• MathML mo element
• MathML ms element
• MathML mtext element

SVG

While support for SVG as a whole is not required by this specification (though it is encouraged, at least for Web browsers), certain features depend upon parts of SVG being implemented.

Also, the SVG specifications do not reflect implementation reality. Implementations implement subsets of SVG 1.1 and SVG Tiny 1.2. Although it is hoped that the in-progress SVG 2 specification is a more realistic target for implementations, until that specification is ready, user agents that implement SVG must do so with the following willful violations and additions. [SVG] [SVGTINY12] [SVG2]

User agents that implement SVG must not implement the following features from SVG 1.1:

• The tref element
• The cursor element (use CSS's cursor property instead)
• The font-defining SVG elements: font, glyph, missing-glyph, hkern, vkern, font-face, font-face-src, font-face-uri, font-face-format, and font-face-name (use CSS's @font-face instead)
• The externalResourcesRequired attribute
• The enable-background property
• The contentScriptType and contentStyleType attributes (use the type attribute on the SVG script and style elements instead)

User agents that implement SVG must implement the following features from SVG Tiny 1.2:

• The non-scaling-stroke value for the vector-effect property
• The class attribute is allowed on all SVG elements
• The tabindex attribute is allowed on visible SVG elements
• The ARIA accessibility attributes are allowed on all SVG elements

The following features are defined in the SVG specifications:

• SVGImageElement interface
• SVGScriptElement interface
• SVGSVGElement interface
• SVG desc element
• SVG foreignObject element
• SVG image element
• SVG script element
• SVG svg element
• SVG title element
• SVG use element

Filter Effects

The following feature is defined in the Filter Effects specification: [FILTERS]

• <filter-function-list>

Worklets

The following feature is defined in the Worklets specification: [WORKLETS]

• WorkletGlobalScope

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This specification does not require support of any particular network protocol, style sheet language, scripting language, or any of the DOM specifications beyond those required in the list above. However, the language described by this specification is biased towards CSS as the styling language, JavaScript as the scripting language, and HTTP as the network protocol, and several features assume that those languages and protocols are in use.

A user agent that implements the HTTP protocol must implement HTTP State Management Mechanism (Cookies) as well. [HTTP] [COOKIES]

This specification might have certain additional requirements on character encodings, image formats, audio formats, and video formats in the respective sections.