HTML: The Living Standard

This specification relies on several other underlying specifications.

Infra

The following terms are defined in Infra: [INFRA]

• The general iteration terms while, continue, and break.
• Assert
• implementation-defined
• tracking vector
• code point and its synonym character
• surrogate
• scalar value
• tuple
• noncharacter
• string, code unit, code unit prefix, code unit less than, starts with, ends with, length, and code point length
• The string equality operations is and identical to
• scalar value string
• convert
• ASCII string
• ASCII tab or newline
• 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
• isomorphic decode
• isomorphic encode
• ASCII lowercase
• ASCII uppercase
• ASCII case-insensitive
• strip newlines
• normalize 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 key, value, empty, entry, exists, getting the value of an entry, setting the value of an entry, removing an entry, clear, getting the keys, getting the values, sorting in descending order, size, and iterate
• The list data structure and the associated definitions for append, extend, prepend, replace, remove, empty, contains, size, indices, is empty, item, iterate, and clone sort in ascending order sort in descending order
• The stack data structure and the associated definitions for push and pop
• The queue data structure and the associated definitions for enqueue and dequeue
• The ordered set data structure and the associated definition for append and union
• The struct specification type and the associated definition for item
• The byte sequence data structure
• The forgiving-base64 encode and forgiving-base64 decode algorithms
• exclusive range
• parse a JSON string to an Infra value
• 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 Encoding 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 Encoding: [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 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
• The BOM sniff algorithm which takes a byte stream and returns an encoding or null.

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 name space in the XML namespace is defined by Extensible Markup Language (XML). [XML]

The Name production is defined in XML. [XML]

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

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

URLs

The following terms are defined in URL: [URL]

• host
• public suffix
• domain
• IP address
• URL
• Origin of URLs
• Absolute URL
• Relative URL
• registrable domain
• The URL parser
• The basic URL parser and its url and state override arguments, 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
  • blob URL entry
• valid URL string
• The cannot have a username/password/port concept
• The opaque path concept
• URL serializer and its exclude fragment argument
• URL path serializer
• The host parser
• The host serializer
• Host equals
• URL equals and its exclude fragments argument
• serialize an integer
• Default encode set
• component percent-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
• is special

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 Media Fragments URI. [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
• `Content-Range` header
• `Last-Modified` header
• `Range` header
• `Referer` header

The following terms are defined in HTTP State Management Mechanism: [COOKIES]

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

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

• `Link` header
• Parsing a `Link` field value

The following terms are defined in Structured Field Values for HTTP: [STRUCTURED-FIELDS]

• structured header
• boolean
• token
• parameters

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

• MIME type
• MIME type essence
• valid MIME type string
• valid MIME type string with no parameters
• HTML MIME type
• JavaScript MIME type and JavaScript MIME type essence match
• JSON MIME type
• XML MIME type
• image MIME type
• audio or video MIME type
• font MIME type
• parse a MIME type
• is MIME type supported by the user agent?

Fetch

The following terms are defined in Fetch: [FETCH]

• ABNF
• about:blank
• An HTTP(S) scheme
• A URL which is local
• A local scheme
• A fetch scheme
• CORS protocol
• default `User-Agent` value
• extract a MIME type
• legacy extract an encoding
• fetch
• fetch controller
• process the next manual redirect
• ok status
• navigation request
• network error
• aborted network error
• `Origin` header
• `Cross-Origin-Resource-Policy` header
• getting a structured field value
• header list
• set
• get, decode, and split
• abort
• cross-origin resource policy check
• the RequestCredentials enumeration
• the RequestDestination enumeration
• the fetch() method
• report timing
• serialize a response URL for reporting
• safely extracting a body
• incrementally reading a body
• processResponseConsumeBody
• processResponseEndOfBody
• processResponse
• useParallelQueue
• processEarlyHintsResponse
• connection pool
• obtain a connection
• determine the network partition key
• extract full timing info
• as a body
• response body info
• resolve an origin
• response and its associated:
  • type
  • URL
  • URL list
  • status
  • header list
  • body
  • body info
  • internal response
  • location URL
  • timing info
  • service worker timing info
  • has-cross-origin-redirects
  • timing allow passed
  • extract content-range values
• request and its associated:
  • URL
  • method
  • header list
  • body
  • client
  • URL list
  • current URL
  • reserved client
  • replaces client id
  • initiator
  • destination
  • potential destination
  • translating a potential destination
  • script-like destinations
  • priority
  • origin
  • referrer
  • synchronous flag
  • mode
  • credentials mode
  • use-URL-credentials flag
  • unsafe-request flag
  • cache mode
  • redirect count
  • redirect mode
  • policy container
  • referrer policy
  • cryptographic nonce metadata
  • integrity metadata
  • parser metadata
  • reload-navigation flag
  • history-navigation flag
  • user-activation
  • render-blocking
  • initiator type
  • add a range header
• fetch timing info and its associated:
  • start time
  • end time

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", "origin-when-cross-origin", and "unsafe-url" referrer policies
• The default referrer policy

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

• a priori authenticated URL

The following terms are defined in Subresource Integrity: [SRI]

• parse integrity metadata
• the requirements of the integrity attribute
• get the strongest metadata from set

Paint Timing

The following terms are defined in Paint Timing: [PAINTTIMING]

• mark paint timing

Navigation Timing

The following terms are defined in Navigation Timing: [NAVIGATIONTIMING]

• create the navigation timing entry
• queue the navigation timing entry
• NavigationTimingType and its "navigate", "reload", and "back_forward" values.

Resource Timing

The following terms are defined in Resource Timing: [RESOURCETIMING]

• Mark resource timing

Performance Timeline

The following terms are defined in Performance Timeline: [PERFORMANCETIMELINE]

• PerformanceEntry and its name, entryType, startTime, and duration attributes.
• Queue a performance entry

Long Animation Frames

The following terms are defined in Long Animation Frames: [LONGANIMATIONFRAMES]

• record task start time
• record task end time
• record rendering time
• record classic script creation time
• record classic script execution start time
• record module script execution start time
• Record pause duration
• record timing info for timer handler
• record timing info for microtask checkpoint

Long Tasks

The following terms are defined in Long Tasks: [LONGTASKS]

• report long tasks

Web IDL

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

The following terms are defined in Web IDL:

• this
• extended attribute
• named constructor
• constructor operation
• overridden constructor steps
• internally create a new object implementing the interface
• array index property name
• supports indexed properties
• 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
• legacy platform object
• primary interface
• interface object
• named properties object
• include
• inherit
• interface prototype object
• implements
• associated realm
• [[Realm]] field of a platform object
• [[GetOwnProperty]] internal method of a named properties object
• callback context
• frozen array and creating a frozen array
• create a new object implementing the interface
• callback this value
• converting between Web IDL types and JS types
• invoking and constructing callback functions
• overload resolution algorithm
• exposed
• a promise resolved with
• a promise rejected with
• wait for all
• upon rejection
• upon fulfillment
• mark as handled
• [Global]
• [LegacyFactoryFunction]
• [LegacyLenientThis]
• [LegacyNullToEmptyString]
• [LegacyOverrideBuiltIns]
• LegacyPlatformObjectGetOwnProperty
• [LegacyTreatNonObjectAsNull]
• [LegacyUnenumerableNamedProperties]
• [LegacyUnforgeable]
• set entries

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

• ArrayBuffer
• ArrayBufferView
• boolean
• DOMString
• double
• enumeration
• Function
• long
• object
• Promise
• Uint8ClampedArray
• unrestricted double
• unsigned long
• USVString
• VoidFunction

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

• "IndexSizeError"
• "HierarchyRequestError"
• "InvalidCharacterError"
• "NoModificationAllowedError"
• "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]

The term "JavaScript" is used to refer to ECMA-262, rather than the official term ECMAScript, since the term JavaScript is more widely known.

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

• active function object
• agent and agent cluster
• automatic semicolon insertion
• candidate execution
• The current realm
• clamping a mathematical value
• early error
• forward progress
• invariants of the essential internal methods
• JavaScript execution context
• JavaScript execution context stack
• realm
• JobCallback Record
• NewTarget
• running JavaScript execution context
• surrounding agent
• abstract closure
• immutable prototype exotic object
• Well-Known Symbols, including %Symbol.hasInstance%, %Symbol.isConcatSpreadable%, %Symbol.toPrimitive%, and %Symbol.toStringTag%
• Well-Known Intrinsic Objects, including %Array.prototype%, %Error.prototype%, %EvalError.prototype%, %Function.prototype%, %JSON.parse%, %Object.prototype%, %Object.prototype.valueOf%, %RangeError.prototype%, %ReferenceError.prototype%, %SyntaxError.prototype%, %TypeError.prototype%, and %URIError.prototype%
• The FunctionBody production
• The Module production
• The Pattern production
• The Script production
• The BigInt, Boolean, Number, String, Symbol, and Object ECMAScript language types
• The Completion Record specification type
• The List and Record specification types
• The Property Descriptor specification type
• The Script Record specification type
• The Cyclic Module Record specification type
• The Source Text Module Record specification type and its Evaluate, Link and LoadRequestedModules methods
• The ArrayCreate abstract operation
• The Call abstract operation
• The ClearKeptObjects abstract operation
• The CleanupFinalizationRegistry abstract operation
• The Construct abstract operation
• The CopyDataBlockBytes abstract operation
• The CreateBuiltinFunction abstract operation
• The CreateByteDataBlock abstract operation
• The CreateDataProperty abstract operation
• The DefinePropertyOrThrow abstract operation
• The DetachArrayBuffer abstract operation
• The EnumerableOwnProperties abstract operation
• The FinishLoadingImportedModule abstract operation
• The OrdinaryFunctionCreate abstract operation
• The Get abstract operation
• The GetActiveScriptOrModule abstract operation
• The GetFunctionRealm abstract operation
• The HasOwnProperty abstract operation
• The HostCallJobCallback abstract operation
• The HostEnqueueFinalizationRegistryCleanupJob abstract operation
• The HostEnqueueGenericJob abstract operation
• The HostEnqueuePromiseJob abstract operation
• The HostEnqueueTimeoutJob abstract operation
• The HostEnsureCanAddPrivateElement abstract operation
• The HostLoadImportedModule abstract operation
• The HostMakeJobCallback abstract operation
• The HostPromiseRejectionTracker 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 NormalCompletion 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 OrdinaryObjectCreate abstract operation
• The ParseModule abstract operation
• The ParseScript abstract operation
• The NewPromiseReactionJob abstract operation
• The NewPromiseResolveThenableJob abstract operation
• The RegExpBuiltinExec abstract operation
• The RegExpCreate 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 IsLooselyEqual abstract operation
• The IsStrictlyEqual abstract operation
• The Atomics object
• The Atomics.waitAsync object
• The Date class
• The FinalizationRegistry class
• The RegExp class
• The SharedArrayBuffer class
• The SyntaxError class
• The TypeError class
• The RangeError class
• The WeakRef class
• The eval() function
• The WeakRef.prototype.deref() function
• The [[IsHTMLDDA]] internal slot
• import()
• import.meta
• The HostGetImportMetaProperties abstract operation
• The typeof operator
• The delete operator
• The TypedArray Constructors table

Users agents that support JavaScript must also implement the Dynamic Code Brand Checks proposal. The following terms are defined there, and used in this specification: [JSDYNAMICCODEBRANDCHECKS]

• The HostEnsureCanCompileStrings abstract operation
• The HostGetCodeForEval abstract operation

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

User agents that support JavaScript must also implement the Import Attributes proposal. The following terms are defined there, and used in this specification: [JSIMPORTATTRIBUTES]

• The ModuleRequest Record specification type
• The HostGetSupportedImportAttributes abstract operation

User agents that support JavaScript must also implement the JSON modules proposal. The following terms are defined there, and used in this specification: [JSJSONMODULES]

• The CreateDefaultExportSyntheticModule abstract operation
• The SetSyntheticModuleExport abstract operation
• The Synthetic Module Record specification type
• The ParseJSONModule abstract operation

User agents that support JavaScript must also implement the Resizable ArrayBuffer and growable SharedArrayBuffer proposal. The following terms are defined there, and used in this specification: [JSRESIZABLEBUFFERS]

• The IsArrayBufferViewOutOfBounds abstract operation

User agents that support JavaScript must also implement the Temporal proposal. The following terms are defined there, and used in this specification: [JSTEMPORAL]

• The HostSystemUTCEpochNanoseconds abstract operation
• The nsMaxInstant and nsMinInstant values

WebAssembly

The following term is defined in WebAssembly JavaScript Interface: [WASMJS]

• WebAssembly.Module

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 DOM: [DOM]

• Attr interface
• CharacterData interface
• Comment interface
• DOMImplementation interface
• Document interface and its doctype attribute
• DocumentOrShadowRoot interface
• DocumentFragment interface
• DocumentType interface
• ChildNode interface
• Element interface
• attachShadow() method.
• An element's shadow root
• A shadow root's mode
• A shadow root's declarative member
• The attach a shadow root algorithm
• The retargeting algorithm
• Node interface
• NodeList interface
• ProcessingInstruction interface
• ShadowRoot interface
• Text interface
• Range interface
• node document concept
• document type concept
• host concept
• The shadow root concept, and its delegates focus, available to element internals, clonable, and serializable.
• The shadow host concept
• HTMLCollection interface, its length attribute, and its item() and namedItem() methods
• The terms collection and represented by the collection
• DOMTokenList interface, and its value attribute and supports operation
• createDocument() method
• createHTMLDocument() method
• createElement() method
• createElementNS() method
• getElementById() method
• getElementsByClassName() method
• append() method
• appendChild() method
• cloneNode() method
• importNode() method
• preventDefault() method
• id attribute
• setAttribute() method
• textContent attribute
• The tree, shadow tree, and node tree concepts
• The tree order and shadow-including tree order concepts
• The element concept
• The child concept
• The root and shadow-including root concepts
• The inclusive ancestor, descendant, shadow-including ancestor, shadow-including descendant, shadow-including inclusive descendant, and shadow-including inclusive ancestor concepts
• The first child, next sibling, previous sibling, and parent concepts
• The parent element concept
• 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 assigned slot concept
• The slot assignment concept
• The slottable concept
• The assign slottables for a tree algorithm
• The slotchange event
• The inclusive descendant concept
• The find flattened slottables algorithm
• The manual slot assignment concept
• The assign a slot algorithm
• The pre-insert, insert, append, replace, replace all, string replace all, remove, and adopt algorithms for nodes
• The descendant concept
• The insertion steps,
• The post-connection steps, removing steps, adopting steps, and children changed steps hooks for elements
• The change, append, remove, replace, get an attribute by namespace and local name, set value, and remove an attribute by namespace and local name algorithms for attributes
• The attribute change steps hook for attributes
• The value concept for attributes
• The local name concept for attributes
• The attribute list concept
• The data of a CharacterData node and its replace data algorithm
• The child text content of a node
• The descendant text content of a node
• The name, public ID, and system ID of a doctype
• Event interface
• Event and derived interfaces constructor behavior
• 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 flag
• The dispatch algorithm
• EventInit dictionary type
• type attribute
• An event's target
• currentTarget attribute
• bubbles attribute
• cancelable attribute
• composed attribute
• composed flag
• isTrusted attribute
• initEvent() method
• add an event listener
• addEventListener() method
• The remove an event listener and remove all event listeners algorithms
• EventListener callback interface
• The type of an event
• An event listener and its type and callback
• The encoding (herein the character encoding), mode, allow declarative shadow roots, 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 clone a node with its arguments document, subtree, and parent, and the concept of cloning steps
• 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 node, 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 namespace, namespace prefix, local name, custom element definition, and is value
• MutationObserver interface and mutation observers in general
• AbortController and its signal
• AbortSignal
• aborted
• signal abort
• add
• The get an attribute by name algorithm

The following features are defined in UI Events: [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
• beforeinput event
• click event
• contextmenu event
• dblclick event
• input 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 Touch Events: [TOUCH]

• Touch interface
• Touch point concept
• touchend event

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

• The PointerEvent interface
• The PointerEvent interface's pointerType attribute
• fire a pointer event
• pointerdown event
• pointerup event
• pointercancel event

The following events are defined in Clipboard API and events: [CLIPBOARD-APIS]

• copy event
• cut event
• paste 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 DOM Parsing and Serialization: [DOMPARSING]

• XML serialization

The following features are defined in Selection API: [SELECTION]

• selection
• Selection

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

The following features are defined in Fullscreen API: [FULLSCREEN]

• requestFullscreen()
• fullscreenchange
• run the fullscreen steps
• fully exit fullscreen
• fullscreen element
• fullscreen flag

High Resolution Time provides the following features: [HRT]

• current high resolution time
• relative high resolution time
• unsafe shared current time
• shared monotonic clock
• unsafe moment
• duration from
• coarsen time
• current wall time
• Unix epoch
• DOMHighResTimeStamp

File API

This specification uses the following features defined in File API: [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
• blob URL entry and its environment
• The obtain a blob object algorithm

Indexed Database API

The following terms are defined in Indexed Database API: [INDEXEDDB]

• cleanup Indexed Database transactions
• IDBVersionChangeEvent

Media Source Extensions

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

• MediaSource interface
• detaching from a media element

Media Capture and Streams

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

• MediaStream interface
• MediaStreamTrack
• live state
• getUserMedia()

Reporting

The following terms are defined in Reporting: [REPORTING]

• Queue a report
• report type
• visible to ReportingObservers

XMLHttpRequest

The following features and terms are defined in XMLHttpRequest: [XHR]

• The XMLHttpRequest interface, and its responseXML attribute
• The ProgressEvent interface, and its lengthComputable, loaded, and total attributes
• The FormData interface, and its associated entry list

Battery Status

The following features are defined in Battery Status API: [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 CSS Syntax must be followed, including error handling rules. [CSSSYNTAX]

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 Cascading Style Sheets (CSS): [CSS]

• viewport
• line box
• out-of-flow
• in-flow
• collapsing margins
• containing block
• inline box
• block box
• The 'top', 'bottom', 'left', and 'right' properties
• The 'float' property
• The 'clear' property
• The 'width' property
• The 'height' property
• The 'min-width' property
• The 'min-height' property
• The 'max-width' property
• The 'max-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 basic version of the 'display' property is defined in CSS, and the property is extended by other CSS modules. [CSS] [CSSRUBY] [CSSTABLE]

The following terms and features are defined in CSS Box Model: [CSSBOX]

• content area
• content box
• border box
• margin box
• border edge
• margin edge
• The 'margin-top', 'margin-bottom', 'margin-left', and 'margin-right' properties
• The 'padding-top', 'padding-bottom', 'padding-left', and 'padding-right' properties

The following features are defined in CSS Logical Properties: [CSSLOGICAL]

• The 'margin-block', 'margin-block-start', 'margin-block-end', 'margin-inline', 'margin-inline-start', and 'margin-inline-end' properties
• The 'padding-block', 'padding-block-start', 'padding-block-end', 'padding-inline', 'padding-inline-start', and 'padding-inline-end' properties
• The 'border-block-width', 'border-block-start-width', 'border-block-end-width', 'border-inline-width', 'border-inline-start-width', 'border-inline-end-width', 'border-block-style', 'border-block-start-style', 'border-block-end-style', 'border-inline-style', 'border-inline-start-style', 'border-inline-end-style', 'border-block-start-color', 'border-block-end-color', 'border-inline-start-color', 'border-inline-end-color', 'border-start-start-radius', 'border-start-end-radius', 'border-end-start-radius', and 'border-end-end-radius' properties
• The 'block-size' property
• The 'inline-size' property
• The 'inset-block-start' property
• The 'inset-block-end' property

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

• named color
• <color>
• The 'color' property
• The 'currentcolor' value
• opaque black
• transparent black
• 'srgb' color space
• 'display-p3' color space
• 'relative-colorimetric' rendering intent
• parse a CSS <color> value
• serialize a CSS <color> value including HTML-compatible serialization is requested
• Converting Colors
• 'color()'

The following terms are defined in CSS Images: [CSSIMAGES]

• default object size
• concrete object size
• natural dimensions
• natural height
• natural width
• The 'image-orientation' property
• 'conic-gradient'
• The 'object-fit' property

The term paint source is used as defined in CSS Images Level 4 to define the interaction of certain HTML elements with the CSS 'element()' function. [CSSIMAGES4]

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

• The 'background-color', 'background-image', 'background-repeat', 'background-attachment', 'background-position', 'background-clip', 'background-origin', and 'background-size' properties
• The 'border-radius', 'border-top-left-radius', 'border-top-right-radius', 'border-bottom-right-radius', 'border-bottom-left-radius' properties
• The 'border-image-source', 'border-image-slice', 'border-image-width', 'border-image-outset', and 'border-image-repeat' properties

CSS Backgrounds and Borders also defines the following border properties: [CSSBG]

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 following features are defined in CSS Box Alignment: [CSSALIGN]

• The 'align-content' property
• The 'align-items' property
• The 'align-self' property
• The 'justify-self' property
• The 'justify-content' property
• The 'justify-items' property

The following terms and features are defined in CSS Display: [CSSDISPLAY]

• outer display type
• inner display type
• block-level
• block container
• formatting context
• block formatting context
• inline formatting context
• replaced element
• CSS box

The following features are defined in CSS Flexible Box Layout: [CSSFLEXBOX]

• The 'flex-direction' property
• The 'flex-wrap' property

The following terms and features are defined in CSS Fonts: [CSSFONTS]

• first available font
• The 'font-family' property
• The 'font-weight' property
• The 'font-size' property
• The 'font' property
• The 'font-kerning' property
• The 'font-stretch' property
• The 'font-variant-caps' property
• The 'small-caps' value
• The 'all-small-caps' value
• The 'petite-caps' value
• The 'all-petite-caps' value
• The 'unicase' value
• The 'titling-caps' value
• The 'ultra-condensed' value
• The 'extra-condensed' value
• The 'condensed' value
• The 'semi-condensed' value
• The 'semi-expanded' value
• The 'expanded' value
• The 'extra-expanded' value
• The 'ultra-expanded' value

The following features are defined in CSS Grid Layout: [CSSGRID]

• The 'grid-auto-columns' property
• The 'grid-auto-flow' property
• The 'grid-auto-rows' property
• The 'grid-column-gap' property
• The 'grid-row-gap' property
• The 'grid-template-areas' property
• The 'grid-template-columns' property
• The 'grid-template-rows' property

The following terms are defined in CSS Inline Layout: [CSSINLINE]

• alphabetic baseline
• ascent metric
• descent metric
• em-over baseline
• em-under baseline
• hanging baseline
• ideographic-under baseline

The following terms and features are defined in CSS Box Sizing: [CSSSIZING]

• fit-content inline size
• 'aspect-ratio' property
• intrinsic size

The following features are defined in CSS Lists and Counters. [CSSLISTS]

• list item
• The 'counter-reset' property
• The 'counter-set' property
• The 'list-style-type' property

The following features are defined in CSS Overflow. [CSSOVERFLOW]

• The 'overflow' property and its 'hidden' value
• The 'text-overflow' property
• The term scroll container

The following terms and features are defined in CSS Positioned Layout: [CSSPOSITION]

• absolutely-positioned
• The 'position' property and its 'static' value
• The top layer (an ordered set)
• add an element to the top layer
• request an element to be removed from the top layer
• remove an element from the top layer immediately
• process top layer removals

The following features are defined in CSS Multi-column Layout. [CSSMULTICOL]

• The 'column-count' property
• The 'column-fill' property
• The 'column-gap' property
• The 'column-rule' property
• The 'column-width' property

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

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

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

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

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

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

• The 'outline' property
• The 'cursor' property
• The 'appearance' property, its <compat-auto> non-terminal value type, its 'textfield' value, and its 'menulist-button' value.
• The 'field-sizing' property, and its 'content' value.
• The concept widget
• The concept native appearance
• The concept primitive appearance
• The concept element with default preferred size
• The non-devolvable widget and devolvable widget classification, and the related devolved widget state.
• The 'pointer-events' property
• The 'user-select' property

The algorithm to update animations and send events is defined in Web Animations. [WEBANIMATIONS]

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
• style IDL attribute
• cssText attribute of CSSStyleDeclaration
• StyleSheet interface
• CSSStyleSheet interface
• create a CSS style sheet
• remove a CSS style sheet
• associated CSS style sheet
• create a constructed CSSStyleSheet
• synchronously replace the rules of a CSSStyleSheet
• disable a 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 a target into view
• Scroll to the beginning of the document
• The resize event
• The scroll event
• The scrollend event
• set up browsing context features

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

• conformant style sheet
• parse a list of component values
• parse a comma-separated list of component values
• component value
• environment encoding
• <whitespace-token>

The following terms are defined in Selectors: [SELECTORS]

• type selector
• attribute selector
• pseudo-class
• :focus-visible pseudo-class
• indicate focus
• pseudo-element

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

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

The following features are defined in CSS View Transitions: [CSSVIEWTRANSITIONS]

• perform pending transition operations
• rendering suppression for view transitions
• activate view transition
• ViewTransition
• view transition page visibility change steps
• resolving inbound cross-document view-transition
• setting up a cross-document view-transition
• can navigation trigger a cross-document view-transition?

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

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

• cascaded value
• specified value
• computed value
• used value
• cascade origin
• Author Origin
• User Origin
• User Agent Origin
• Animation Origin
• Transition Origin
• initial 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 Geometry Interfaces: [GEOMETRY]

• DOMMatrix interface, and associated m11 element, m12 element, m21 element, m22 element, m41 element, and m42 element
• DOMMatrix2DInit and DOMMatrixInit dictionaries
• The create a DOMMatrix from a dictionary and create a DOMMatrix from a 2D dictionary algorithms for DOMMatrix2DInit or DOMMatrixInit
• The DOMPointInit dictionary, and associated x and y members
• Matrix multiplication

The following terms are defined in the CSS Scoping: [CSSSCOPING]

• flat tree

The following terms and features are defined in CSS Color Adjustment: [CSSCOLORADJUST]

• 'color-scheme'
• page's supported color-schemes

The following terms are defined in CSS Pseudo-Elements: [CSSPSEUDO]

• '::details-content'
• '::file-selector-button'

The following terms are defined in CSS Containment: [CSSCONTAIN]

• skips its contents
• relevant to the user
• proximity to the viewport
• layout containment
• 'content-visibility' property
• 'auto' value for 'content-visibility'

The following terms are defined in CSS Anchor Positioning: [CSSANCHOR]

• implicit anchor element

Intersection Observer

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

• run the update intersection observations steps
• IntersectionObserver
• IntersectionObserverInit
• observe
• unobserve
• isIntersecting
• target

Resize Observer

The following terms are defined in Resize Observer: [RESIZEOBSERVER]

• gather active resize observations at depth
• has active resize observations
• has skipped resize observations
• broadcast active resize observations
• deliver resize loop error

WebGL

The following interfaces are defined in the WebGL specifications: [WEBGL]

• WebGLRenderingContext interface
• WebGL2RenderingContext interface
• WebGLContextAttributes dictionary

WebGPU

The following interfaces are defined in WebGPU: [WEBGPU]

• GPUCanvasContext interface

WebVTT

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

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

• WebVTT file
• WebVTT file using cue 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

ARIA

The role attribute is defined in Accessible Rich Internet Applications (ARIA), as are the following roles: [ARIA]

• button
• presentation

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

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

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

• role
• accessible name
• The ARIAMixin interface, with its associated ARIAMixin getter steps and ARIAMixin setter steps hooks

Content Security Policy

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

• Content Security Policy
• disposition
• directive set
• Content Security Policy directive
• CSP list
• The Content Security Policy syntax
• enforce the policy
• The parse a serialized Content Security Policy algorithm
• The Run CSP initialization for a Document algorithm
• The Run CSP initialization for a global object algorithm
• The Should element's inline behavior be blocked by Content Security Policy? algorithm
• The Should navigation request of type be blocked by Content Security Policy? algorithm
• The Should navigation response to navigation request of type 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 contains a header-delivered Content Security Policy property.
• The Parse a response's Content Security Policies algorithm.
• SecurityPolicyViolationEvent interface
• The securitypolicyviolation event

Service Workers

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

• active worker
• client message queue
• control
• handle fetch
• match service worker registration
• service worker
• service worker client
• service worker registration
• ServiceWorker interface
• ServiceWorkerContainer interface
• ServiceWorkerGlobalScope interface
• unregister

Secure Contexts

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

• Is url potentially trustworthy?

Permissions Policy

The following terms are defined in Permissions Policy: [PERMISSIONSPOLICY]

• permissions policy
• policy-controlled feature
• container policy
• serialized permissions policy
• default allowlist
• The creating a permissions policy algorithm
• The creating a permissions policy from a response algorithm
• The is feature enabled by policy for origin algorithm
• The process permissions policy attributes algorithm

Payment Request API

The following feature is defined in Payment Request API: [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 Mathematical Markup Language (MathML):

• 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.

User agents that implement SVG must implement the SVG 2 specification, and not any earlier revisions.

The following features are defined in the SVG 2 specification: [SVG]

• SVGElement interface
• SVGImageElement interface
• SVGScriptElement interface
• SVGSVGElement interface
• SVG a element
• SVG desc element
• SVG foreignObject element
• SVG image element
• SVG script element
• SVG svg element
• SVG title element
• SVG use element
• SVG text-rendering property

Filter Effects

The following features are defined in Filter Effects: [FILTERS]

• <filter-value-list>

Compositing

The following features are defined in Compositing and Blending: [COMPOSITE]

• <blend-mode>
• <composite-mode>
• source-over
• copy

Cooperative Scheduling of Background Tasks

The following features are defined in Cooperative Scheduling of Background Tasks: [REQUESTIDLECALLBACK]

• requestIdleCallback()
• start an idle period algorithm

Screen Orientation

The following terms are defined in Screen Orientation: [SCREENORIENTATION]

• screen orientation change steps

Storage

The following terms are defined in Storage: [STORAGE]

• obtain a local storage bottle map
• obtain a session storage bottle map
• obtain a storage key for non-storage purposes
• storage key equal
• storage proxy map
• legacy-clone a traversable storage shed

Web App Manifest

The following features are defined in Web App Manifest: [MANIFEST]

• application manifest
• installed web application
• process the manifest

WebAssembly JavaScript Interface: ESM Integration

The following terms are defined in WebAssembly JavaScript Interface: ESM Integration: [WASMESM]

• WebAssembly Module Record
• parse a WebAssembly module

WebCodecs

The following features are defined in WebCodecs: [WEBCODECS]

• VideoFrame interface.
• [[display width]]
• [[display height]]

WebDriver

The following terms are defined in WebDriver: [WEBDRIVER]

• extension command
• remote end steps
• WebDriver error
• WebDriver error code
• invalid argument
• getting a property
• success
• WebDriver's security considerations
• current browsing context

WebDriver BiDi

The following terms are defined in WebDriver BiDi: [WEBDRIVERBIDI]

• WebDriver BiDi navigation status
• navigation status id
• navigation status status
• navigation status canceled
• navigation status pending
• navigation status complete
• navigation status url
• WebDriver BiDi navigation started
• WebDriver BiDi navigation aborted
• WebDriver BiDi navigation failed
• WebDriver BiDi download started
• WebDriver BiDi fragment navigated
• WebDriver BiDi DOM content loaded
• WebDriver BiDi load complete
• WebDriver BiDi history updated
• WebDriver BiDi navigable created
• WebDriver BiDi navigable destroyed
• WebDriver BiDi user prompt closed
• WebDriver BiDi user prompt opened

Web Cryptography API

The following terms are defined in Web Cryptography API: [WEBCRYPTO]

• generating a random UUID

WebSockets

The following terms are defined in WebSockets: [WEBSOCKETS]

• WebSocket
• make disappear

WebTransport

The following terms are defined in WebTransport: [WEBTRANSPORT]

• WebTransport
• context cleanup steps

Web Authentication: An API for accessing Public Key Credentials

The following terms are defined in Web Authentication: An API for accessing Public Key Credentials: [WEBAUTHN]

• public key credential

Credential Management

The following terms are defined in Credential Management: [CREDMAN]

• conditional mediation
• credential
• navigator.credentials.get()

Console

The following terms are defined in Console: [CONSOLE]

• report a warning to the console

Web Locks API

The following terms are defined in Web Locks API: [WEBLOCKS]

• locks
• lock requests

Trusted Types

This specification uses the following features defined in Trusted Types: [TRUSTED-TYPES]

• TrustedHTML
• data
• TrustedScript
• data
• TrustedScriptURL
• Get Trusted Type compliant string

WebRTC API

The following terms are defined in WebRTC API: [WEBRTC]

• RTCDataChannel
• RTCPeerConnection

Picture-in-Picture API

The following terms are defined in Picture-in-Picture API: [PICTUREINPICTURE]

• PictureInPictureWindow

Idle Detection API

The following terms are defined in Idle Detection API:

• IdleDetector

Web Speech API

The following terms are defined in Web Speech API:

• SpeechRecognition

WebOTP API

The following terms are defined in WebOTP API:

• OTPCredential

Web Share API

The following terms are defined in Web Share API:

• share()

Web Smart Card API

The following terms are defined in Web Smart Card API:

• SmartCardConnection

Web Background Synchronization

The following terms are defined in Web Background Synchronization:

• SyncManager
• register()

Web Periodic Background Synchronization

The following terms are defined in Web Periodic Background Synchronization:

• PeriodicSyncManager
• register()

Web Background Fetch

The following terms are defined in Background Fetch:

• BackgroundFetchManager
• fetch()

Keyboard Lock

The following terms are defined in Keyboard Lock:

• Keyboard
• lock()

Web MIDI API

The following terms are defined in Web MIDI API:

• requestMIDIAccess()

Generic Sensor API

The following terms are defined in Generic Sensor API:

• request sensor access

WebHID API

The following terms are defined in WebHID API:

• requestDevice

WebXR Device API

The following terms are defined in WebXR Device API:

• XRSystem

---

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.