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<?xml version='1.0'?>
<!--
index.xml
Web IDL (Second Edition)
This is written in XHTML 1.0 Strict with an inline <options> element that
helps the WebIDL.xsl stylesheet process the document (generating a table
of contents, section numbers, certain processing instructions).
-->
<?xml-stylesheet href='WebIDL.xsl' type='text/xsl'?>
<html xmlns='http://www.w3.org/1999/xhtml' xmlns:x='http://mcc.id.au/ns/local' xml:lang='en'>
<head>
<meta http-equiv='Content-Type' content='text/html; charset=UTF-8'/>
<title>Web IDL (Second Edition)</title>
<link rel='stylesheet' href='WebIDL.css' type='text/css'/>
<script src='section-links.js' type='application/ecmascript'/>
<script src='dfn.js' type='application/ecmascript'/>
<options xmlns='http://mcc.id.au/ns/local'>
<versions>
<cvs href='http://heycam.github.io/webidl/'/>
<this href='http://www.w3.org/TR/2012/WD-WebIDL-2012xxxx/'/>
<latest href='http://www.w3.org/TR/WebIDL/'/>
<previous href='http://www.w3.org/TR/2012/CR-WebIDL-20120419/'/>
<previous href='http://www.w3.org/TR/2012/WD-WebIDL-20120207/'/>
<previous href='http://www.w3.org/TR/2011/WD-WebIDL-20110927/'/>
<previous href='http://www.w3.org/TR/2011/WD-WebIDL-20110712/'/>
<previous href='http://www.w3.org/TR/2010/WD-WebIDL-20101021/'/>
<previous href='http://www.w3.org/TR/2008/WD-WebIDL-20081219/'/>
<previous href='http://www.w3.org/TR/2008/WD-WebIDL-20080829/'/>
<previous href='http://www.w3.org/TR/2008/WD-DOM-Bindings-20080410/'/>
<previous href='http://www.w3.org/TR/2007/WD-DOM-Bindings-20071017/'/>
</versions>
<editors>
<person homepage='http://mcc.id.au/' email='[email protected]'>
<name>Cameron McCormack</name>
<affiliation>Mozilla Corporation</affiliation>
</person>
<person email='[email protected]'>
<name>Boris Zbarsky</name>
<affiliation>Mozilla Corporation</affiliation>
</person>
</editors>
<participate>
<mailing-list email='[email protected]'/>
<bugzilla
file='https://www.w3.org/Bugs/Public/enter_bug.cgi?product=WebAppsWG&component=WebIDL'
open='https://www.w3.org/Bugs/Public/buglist.cgi?product=WebAppsWG&component=WebIDL&resolution=---'/>
</participate>
<maturity>ED</maturity>
<links>
<term name='Unicode scalar value' class='external' href='http://www.unicode.org/glossary/#unicode_scalar_value'/>
<term name='Unicode scalar values' class='external' href='http://www.unicode.org/glossary/#unicode_scalar_value'/>
<term name='NumericLiteral' class='external' href='https://tc39.github.io/ecma262/#sec-literals-numeric-literals' ref='ECMA-262' section='11.8.3'/>
<term name='ECMAScript error objects' class='external' href='https://tc39.github.io/ecma262/#sec-error-objects' ref='ECMA-262' section='19.5'/>
<term name='ToBoolean' class='external' href='https://tc39.github.io/ecma262/#sec-toboolean'/>
<term name='ToNumber' class='external' href='https://tc39.github.io/ecma262/#sec-tonumber'/>
<term name='ToUint16' class='external' href='https://tc39.github.io/ecma262/#sec-touint16'/>
<term name='ToInt32' class='external' href='https://tc39.github.io/ecma262/#sec-toint32'/>
<term name='ToUint32' class='external' href='https://tc39.github.io/ecma262/#sec-touint32'/>
<term name='ToString' class='external' href='https://tc39.github.io/ecma262/#sec-tostring'/>
<term name='ToObject' class='external' href='https://tc39.github.io/ecma262/#sec-toobject'/>
<term name='IsAccessorDescriptor' class='external' href='https://tc39.github.io/ecma262/#sec-isaccessordescriptor'/>
<term name='IsDataDescriptor' class='external' href='https://tc39.github.io/ecma262/#sec-isdatadescriptor'/>
<term name='Type' class='external' href='https://tc39.github.io/ecma262/#sec-ecmascript-data-types-and-values'/>
<term name='sign' class='external' href='https://tc39.github.io/ecma262/#sec-algorithm-conventions'/>
<term name='floor' class='external' href='https://tc39.github.io/ecma262/#sec-algorithm-conventions'/>
<term name='abs' class='external' href='https://tc39.github.io/ecma262/#sec-algorithm-conventions'/>
<term name='modulo' class='external' href='https://tc39.github.io/ecma262/#sec-algorithm-conventions'/>
<term name='element' class='external' href='https://tc39.github.io/ecma262/#sec-ecmascript-language-types-string-type'/>
<term name='IsCallable' class='external' href='https://tc39.github.io/ecma262/#sec-iscallable'/>
<term name='callable' class='external' href='https://tc39.github.io/ecma262/#sec-iscallable'/>
<term name='%ArrayPrototype%' class='external' href='https://tc39.github.io/ecma262/#sec-well-known-intrinsic-objects' ref='ECMA-262' section='6.1.7.4'/>
<term name='%ArrayProto_values%' class='external' href='https://tc39.github.io/ecma262/#sec-well-known-intrinsic-objects' ref='ECMA-262' section='6.1.7.4'/>
<term name='%MapPrototype%' class='external' href='https://tc39.github.io/ecma262/#sec-well-known-intrinsic-objects' ref='ECMA-262' section='6.1.7.4'/>
<term name='%ObjectPrototype%' class='external' href='https://tc39.github.io/ecma262/#sec-well-known-intrinsic-objects' ref='ECMA-262' section='6.1.7.4'/>
<term name='%SetPrototype%' class='external' href='https://tc39.github.io/ecma262/#sec-well-known-intrinsic-objects' ref='ECMA-262' section='6.1.7.4'/>
<term name='%Error%' class='external' href='https://tc39.github.io/ecma262/#sec-well-known-intrinsic-objects' ref='ECMA-262' section='6.1.7.4'/>
<term name='%ErrorPrototype%' class='external' href='https://tc39.github.io/ecma262/#sec-well-known-intrinsic-objects' ref='ECMA-262' section='6.1.7.4'/>
<term name='%FunctionPrototype%' class='external' href='https://tc39.github.io/ecma262/#sec-well-known-intrinsic-objects' ref='ECMA-262' section='6.1.7.4'/>
<term name='%ObjProto_toString%' class='external' href='https://tc39.github.io/ecma262/#sec-well-known-intrinsic-objects' ref='ECMA-262' section='6.1.7.4'/>
<term name='%Promise%' class='external' href='https://tc39.github.io/ecma262/#sec-promise-constructor'/>
<term name='%IteratorPrototype%' class='external' href='https://tc39.github.io/ecma262/#sec-well-known-intrinsic-objects' ref='ECMA-262' section='6.1.7.4'/>
<term name='Property Descriptor' class='external' href='https://tc39.github.io/ecma262/#sec-property-descriptor-specification-type' ref='ECMA-262' section='6.2.4'/>
<term name='array index' class='external' href='https://tc39.github.io/ecma262/#sec-array-exotic-objects' ref='ECMA-262' section='9.4.2'/>
<term name='default [[GetOwnProperty]] internal method' class='external' href='https://tc39.github.io/ecma262/#sec-ordinary-object-internal-methods-and-internal-slots-getownproperty-p' ref='ECMA-262' section='9.1.5'/>
<term name='OrdinaryDefineOwnProperty' class='external' href='https://tc39.github.io/ecma262/#sec-ordinarydefineownproperty'/>
<term name='default [[Set]] internal method' class='external' href='https://tc39.github.io/ecma262/#sec-ordinary-object-internal-methods-and-internal-slots-set-p-v-receiver' ref='ECMA-262' section='9.1.9'/>
<term name='equally close values' class='external' href='https://tc39.github.io/ecma262/#sec-ecmascript-language-types-number-type' ref='ECMA-262' section='6.1.6'/>
<term name='internal slot' class='external' href='https://tc39.github.io/ecma262/#sec-object-internal-methods-and-internal-slots'/>
<term name='JavaScript execution context stack' class='external' href='https://tc39.github.io/ecma262/#execution-context-stack'/>
<term name='running JavaScript execution context' class='external' href='https://tc39.github.io/ecma262/#running-execution-context'/>
<term name="ReturnIfAbrupt" class='external'
href='https://tc39.github.io/ecma262/#sec-returnifabrupt'/>
<term name='GetMethod' class='external'
href='http://www.ecma-international.org/ecma-262/6.0/#sec-getmethod'/>
<term name='GetIterator' class='external'
href='https://tc39.github.io/ecma262/#sec-getiterator'/>
<term name='IteratorStep' class='external'
href='https://tc39.github.io/ecma262/#sec-iteratorstep'/>
<term name='NormalCompletion' class='external'
href='https://tc39.github.io/ecma262/#sec-normalcompletion'/>
<term name='IteratorValue' class='external'
href='https://tc39.github.io/ecma262/#sec-iteratorvalue'/>
<term name='@@iterator' class='external'
href='https://tc39.github.io/ecma262/#sec-well-known-symbols'/>
<term name='@@toStringTag' class='external'
href='https://tc39.github.io/ecma262/#sec-well-known-symbols'/>
<term name='@@unscopables' class='external'
href='http://www.ecma-international.org/ecma-262/6.0/#sec-well-known-symbols'/>
<term name='CreateArrayIterator' class='external'
href='https://tc39.github.io/ecma262/#sec-createarrayiterator'/>
<term name='CreateIterResultObject' class='external'
href='https://tc39.github.io/ecma262/#sec-createiterresultobject'/>
<term name='CreateMapIterator' class='external'
href='https://tc39.github.io/ecma262/#sec-createmapiterator'/>
<term name='CreateSetIterator' class='external'
href='https://tc39.github.io/ecma262/#sec-createsetiterator'/>
<term name='ArrayCreate' class='external'
href='https://tc39.github.io/ecma262/#sec-arraycreate'/>
<term name='CreateDataProperty' class='external'
href='https://tc39.github.io/ecma262/#sec-createdataproperty'/>
<term name='DetachArrayBuffer' class='external'
href='https://tc39.github.io/ecma262/#sec-detacharraybuffer'/>
<term name='IsDetachedBuffer' class='external'
href='https://tc39.github.io/ecma262/#sec-isdetachedbuffer'/>
<term name='SetIntegrityLevel' class='external'
href='https://tc39.github.io/ecma262/#sec-setintegritylevel'/>
<term name='array iterator object' class='external'
href='https://tc39.github.io/ecma262/#sec-array-iterator-objects'/>
<term name='array iterator objects' class='external'
href='https://tc39.github.io/ecma262/#sec-array-iterator-objects'/>
<term name='Call' class='external'
href='https://tc39.github.io/ecma262/#sec-call'/>
<term name='Get' class='external'
href='https://tc39.github.io/ecma262/#sec-get-o-p'/>
<term name='Set' class='external'
href='https://tc39.github.io/ecma262/#sec-set-o-p-v-throw'/>
<term name='IsConstructor' class='external'
href='https://tc39.github.io/ecma262/#sec-isconstructor'/>
<term name='Construct' class='external'
href='https://tc39.github.io/ecma262/#sec-construct'/>
<term name='DefinePropertyOrThrow' class='external'
href='https://tc39.github.io/ecma262/#sec-definepropertyorthrow'/>
<term name='Realm' class='external'
href='https://tc39.github.io/ecma262/#sec-code-realms'/>
<term name='Completion' class='external'
href='https://tc39.github.io/ecma262/#sec-completion-record-specification-type'/>
<term name='!' class='external'
href='https://tc39.github.io/ecma262/#sec-algorithm-conventions'/>
<term name='?' class='external'
href='https://tc39.github.io/ecma262/#sec-algorithm-conventions'/>
<term name='relevant settings object' class='external'
href='https://html.spec.whatwg.org/multipage/webappapis.html#relevant-settings-object'/>
<term name='relevant Realm' class='external'
href='https://html.spec.whatwg.org/multipage/webappapis.html#concept-relevant-realm'/>
<term name='secure context' class='external'
href='https://w3c.github.io/webappsec-secure-contexts/#secure-context'/>
<term name='Prepare to run script' class='external'
href='https://html.spec.whatwg.org/multipage/webappapis.html#prepare-to-run-script'/>
<term name='Clean up after running script' class='external'
href='https://html.spec.whatwg.org/multipage/webappapis.html#clean-up-after-running-script'/>
<term name='Prepare to run a callback' class='external'
href='https://html.spec.whatwg.org/multipage/webappapis.html#prepare-to-run-a-callback'/>
<term name='Clean up after running a callback' class='external'
href='https://html.spec.whatwg.org/multipage/webappapis.html#clean-up-after-running-a-callback'/>
<term name='incumbent settings object' class='external'
href='https://html.spec.whatwg.org/multipage/webappapis.html#incumbent-settings-object'/>
</links>
</options>
</head>
<body>
<?top?>
<!--
<div id='publication-warning'>
<strong>This document is in the process of being prepared to be published as a Candidate Recommendation.
Please note that it as yet has not been published as a CR and that this document
at dev.w3.org is still to be considered an unofficial draft.</strong> <br/> <button onclick="document.body.removeChild(this.parentNode)">Dismiss</button>
</div>
-->
<div class='section'>
<h2>Abstract</h2>
<p>
This document defines an interface definition language, Web IDL,
that can be used to describe interfaces that are intended to be
implemented in web browsers. Web IDL is an IDL variant with a
number of features that allow the behavior of common script objects in
the web platform to be specified more readily. How interfaces
described with Web IDL correspond to constructs within ECMAScript
execution environments is also detailed in this document.
It is expected that this document acts
as a guide to implementors of already-published specifications,
and that newly published specifications reference this
document to ensure conforming implementations of interfaces
are interoperable.
</p>
<!-- XXX
Things to consider that aren't in ednotes:
* Consistent linking to term definitions.
* Consistent capitalisation and naming of algorithm variables.
Potential V2 features:
* Parameterized interface types, for BlahLists
http://www.w3.org/mid/[email protected]
-->
<!--
<?revision-note http://www.w3.org/Bugs/Public/buglist.cgi?query_format=advanced&short_desc_type=allwordssubstr&short_desc=&product=WebAppsWG&component=WebIDL&longdesc_type=allwordssubstr&longdesc=&bug_file_loc_type=allwordssubstr&bug_file_loc=&status_whiteboard_type=allwordssubstr&status_whiteboard=&keywords_type=allwords&keywords=&bug_status=NEW&bug_status=ASSIGNED&bug_status=REOPENED&emailtype1=substring&email1=&emailtype2=substring&email2=&bug_id_type=anyexact&bug_id=&votes=&chfieldfrom=&chfieldto=Now&chfieldvalue=&cmdtype=doit&order=Importance&field0-0-0=noop&type0-0-0=noop&value0-0-0=?>
-->
</div>
<div class='section'>
<h2 id='sotd'>Status of This Document</h2>
<?sotd-top [email protected] http://lists.w3.org/Archives/Public/public-script-coord/?>
<p>
This is the Second Edition of Web IDL, branched off from the
Candidate Recommendation of the First Edition. This Second
Edition includes new features that could not have been added
to the First Edition without delaying its progress along the
Recommendation track.
</p>
<p>
This document is produced by the
<a href='https://www.w3.org/WebPlatform/WG/'>Web Platform Working Group</a>
in the W3C <a href='http://www.w3.org/Interaction/'>Interaction Domain</a>.
Changes made to this document can be found in the specification’s
commit log on GitHub:
<a href='https://github.com/heycam/webidl/commits/gh-pages/index.xml'>recent changes</a>,
<a href='https://github.com/heycam/webidl/commits/gh-pages/Overview.xml'>older changes</a>.
</p>
<p>
<!--In addition to the issues marked by editorial notes in this document,-->
There is a <a href='https://www.w3.org/Bugs/Public/buglist.cgi?query_format=advanced&short_desc_type=allwordssubstr&short_desc=&product=WebAppsWG&component=WebIDL&longdesc_type=allwordssubstr&longdesc=&bug_file_loc_type=allwordssubstr&bug_file_loc=&status_whiteboard_type=allwordssubstr&status_whiteboard=&keywords_type=allwords&keywords=&bug_status=UNCONFIRMED&bug_status=NEW&bug_status=ASSIGNED&bug_status=REOPENED&emailtype1=substring&email1=&emailtype2=substring&email2=&bug_id_type=anyexact&bug_id=&votes=&chfieldfrom=&chfieldto=Now&chfieldvalue=&cmdtype=doit&order=Reuse%20same%20sort%20as%20last%20time&field0-0-0=noop&type0-0-0=noop&value0-0-0='>bug tracker</a>
for the specification.
</p>
<?sotd-bottom http://www.w3.org/2004/01/pp-impl/83482/status?>
</div>
<div id='toc'>
<h2>Table of Contents</h2>
<?toc sections appendices?>
</div>
<div id='sections'>
<div id='introduction' class='section'>
<h2>Introduction</h2>
<p class='norm'>This section is informative.</p>
<p>
Technical reports published by the W3C that include programming
language interfaces have typically been described using the
Object Management Group’s Interface Definition Language (IDL)
<a href='#ref-OMGIDL'>[OMGIDL]</a>. The IDL provides a means to
describe these interfaces in a language independent manner. Usually,
additional language binding appendices are included in such
documents which detail how the interfaces described with the IDL
correspond to constructs in the given language.
</p>
<p>
However, the bindings in these specifications for the language most
commonly used on the web, ECMAScript, are consistently specified with
low enough precision as to result in interoperability issues. In
addition, each specification must describe the same basic information,
such as DOM interfaces described in IDL corresponding to properties
on the ECMAScript global object, or the <a class='idltype' href='#idl-unsigned-long'>unsigned
long</a> IDL type mapping to the <span class='estype'>Number</span>
type in ECMAScript.
</p>
<p>
This specification defines an IDL language similar to OMG IDL
for use by specifications that define interfaces for Web APIs. A number of extensions are
given to the IDL to support common functionality that previously must
have been written in prose. In addition, precise language bindings
for ECMAScript Edition 6 are given.
</p>
<div id='conventions' class='section'>
<h3>Typographic conventions</h3>
<p>
The following typographic conventions are used in this document:
</p>
<ul>
<li>Defining instances of terms: <dfn id='dfn-example-term'>example term</dfn></li>
<li>Links to terms defined in this document: <a class='dfnref' href='#dfn-example-term'>example term</a></li>
<li>Links to terms defined in other documents: <a class='dfnref external' href='#dfn-example-term'>example term</a></li>
<li>Grammar symbols: <span class='sym'>ExampleGrammarSymbol</span></li>
<li>IDL and ECMAScript types: <span class='idltype'>ExampleType</span></li>
<li>Code snippets: <code>a = b + obj.f()</code></li>
<li>Unicode characters: <span class='char'>U+0030 DIGIT ZERO ("0")</span></li>
<li>Extended attributes: <span class='xattr'>[ExampleExtendedAttribute]</span></li>
<li>Variable names in prose and algorithms: <var>exampleVariableName</var>.</li>
<li>Algorithms use <a href="https://tc39.github.io/ecma262/#sec-algorithm-conventions">the conventions of the ECMAScript specification</a>, including the ! and ? notation for unwrapping completion records.</li>
<li>IDL informal syntax examples:
<pre class='syntax'>interface <i>identifier</i> {
<em>interface-members…</em>
};</pre>
(Red text is used to highlight specific parts of the syntax discussed in surrounding prose.)</li>
<li>IDL grammar snippets:
<table class='grammar'>
<tr><td><span class='prod-number'>[5]</span></td><td><span class='sym'>ExampleGrammarSymbol</span></td><td class='prod-mid'>→</td><td><span class='prod-lines'>OtherSymbol "sometoken"<br/> | AnotherSymbol<br/> | ε <span class='comment'>// nothing</span></span></td></tr>
</table>
(Each grammar rule is assigned a number for reference, shown on the left.)</li>
<li>Non-normative notes: <div class='note'><p>This is a note.</p></div></li>
<li>Non-normative examples: <div class='example'><p>This is an example.</p></div></li>
<li>Normative warnings: <div class='warning'><p>This is a warning.</p></div></li>
<li>Code blocks: <x:codeblock language='idl'><span class='comment'>// This is an IDL code block.</span>
interface Example {
attribute long something;
};</x:codeblock>
<x:codeblock language='es'><span class='comment'>// This is an ECMAScript code block.</span>
window.onload = function() { window.alert("loaded"); };</x:codeblock></li>
</ul>
</div>
</div>
<div id='conformance' class='section'>
<h2>Conformance</h2>
<p>
Everything in this specification is normative except for diagrams,
examples, notes and sections marked as being informative.
</p>
<p>
The keywords “<span class='rfc2119'>MUST</span>”,
“<span class='rfc2119'>MUST NOT</span>”,
“<span class='rfc2119'>REQUIRED</span>”,
“<span class='rfc2119'>SHALL</span>”,
“<span class='rfc2119'>SHALL NOT</span>”,
“<span class='rfc2119'>SHOULD</span>”,
“<span class='rfc2119'>SHOULD NOT</span>”,
“<span class='rfc2119'>RECOMMENDED</span>”,
“<span class='rfc2119'>MAY</span>” and
“<span class='rfc2119'>OPTIONAL</span>” in this document are to be
interpreted as described in
<cite><a href='http://tools.ietf.org/html/rfc2119'>Key words for use in RFCs to
Indicate Requirement Levels</a></cite>
<a href='#ref-RFC2119'>[RFC2119]</a>.
</p>
<p>
The following conformance classes are defined by this specification:
</p>
<dl>
<dt><dfn data-export="" id='dfn-conforming-set-of-idl-fragments'>conforming set of IDL fragments</dfn></dt>
<dd>
<p>
A set of <a class='dfnref' href='#dfn-idl-fragment'>IDL fragments</a> is considered
to be a <a class='dfnref' href='#dfn-conforming-set-of-idl-fragments'>conforming
set of IDL fragments</a> if, taken together, they satisfy all of the
<span class='rfc2119'>MUST</span>-,
<span class='rfc2119'>REQUIRED</span>- and <span class='rfc2119'>SHALL</span>-level
criteria in this specification that apply to IDL fragments.
</p>
</dd>
<dt><dfn data-export="" id='dfn-conforming-implementation'>conforming implementation</dfn></dt>
<dd>
<p>
A user agent is considered to be a
<a class='dfnref' href='#dfn-conforming-implementation'>conforming implementation</a>
relative to a <a class='dfnref' href='#dfn-conforming-set-of-idl-fragments'>conforming
set of IDL fragments</a> if it satisfies all of the <span class='rfc2119'>MUST</span>-,
<span class='rfc2119'>REQUIRED</span>- and <span class='rfc2119'>SHALL</span>-level
criteria in this specification that apply to implementations for all language
bindings that the user agent supports.
</p>
</dd>
<dt><dfn data-export="" id='dfn-conforming-ecmascript-implementation'>conforming ECMAScript implementation</dfn></dt>
<dd>
<p>
A user agent is considered to be a
<a class='dfnref' href='#dfn-conforming-ecmascript-implementation'>conforming ECMAScript implementation</a>
relative to a <a class='dfnref' href='#dfn-conforming-set-of-idl-fragments'>conforming
set of IDL fragments</a> if it satisfies all of the <span class='rfc2119'>MUST</span>-,
<span class='rfc2119'>REQUIRED</span>- and <span class='rfc2119'>SHALL</span>-level
criteria in this specification that apply to implementations for the ECMAScript
language binding.
</p>
</dd>
</dl>
</div>
<div id='idl' class='section'>
<h2>Interface definition language</h2>
<p>
This section describes a language, <em>Web IDL</em>, which can be used to define
interfaces for APIs in the Web platform. A specification that defines Web APIs
can include one or more <dfn data-export="" data-lt="IDL fragment" id='dfn-idl-fragment'>IDL fragments</dfn> that
describe the interfaces (the state and behavior that objects can exhibit)
for the APIs defined by that specification.
An <a class='dfnref' href='#dfn-idl-fragment'>IDL fragment</a> is
a sequence of definitions that matches the <a class='sym' href='#prod-Definitions'>Definitions</a> grammar symbol.
The set of <a class='dfnref' href='#dfn-idl-fragment'>IDL fragments</a> that
an implementation supports is not ordered.
See <a href='#idl-grammar'>Appendix <?sref idl-grammar?></a> for the complete grammar and an explanation of the notation used.
</p>
<p>
The different kinds of <dfn id='dfn-definition'>definitions</dfn> that can appear in an
<a class='dfnref' href='#dfn-idl-fragment'>IDL fragment</a> are:
<a class='dfnref' href='#dfn-interface'>interfaces</a>,
<a class='dfnref' href='#dfn-partial-interface'>partial interface definitions</a>,
<a class='dfnref' href='#dfn-dictionary'>dictionaries</a>,
<a class='dfnref' href='#dfn-partial-dictionary'>partial dictionary definitions</a>,
<a class='dfnref' href='#dfn-typedef'>typedefs</a> and
<a class='dfnref' href='#dfn-implements-statement'>implements statements</a>.
These are all defined in the following sections.
</p>
<p>
Each <a class='dfnref' href='#dfn-definition'>definition</a>
(matching <a class='sym' href='#prod-Definition'>Definition</a>)
can be preceded by a list of <a class='dfnref' href='#dfn-extended-attribute'>extended attributes</a> (matching
<a class='sym' href='#prod-ExtendedAttributeList'>ExtendedAttributeList</a>),
which can control how the definition will be handled in language bindings.
The extended attributes defined by this specification that are language binding
agnostic are discussed in <a href='#idl-extended-attributes'>section <?sref idl-extended-attributes?></a>,
while those specific to the ECMAScript language binding are discussed
in <a href='#es-extended-attributes'>section <?sref es-extended-attributes?></a>.
</p>
<pre class='syntax'>[<em>extended-attributes</em>]
interface <i>identifier</i> {
<i>interface-members…</i>
};</pre>
<?productions grammar Definitions Definition CallbackOrInterface?>
<div class='example'>
<p>
The following is an example of an <a class='dfnref' href='#dfn-idl-fragment'>IDL fragment</a>.
</p>
<x:codeblock language='idl'>interface Paint { };
interface SolidColor : Paint {
attribute double red;
attribute double green;
attribute double blue;
};
interface Pattern : Paint {
attribute DOMString imageURL;
};
[Constructor]
interface GraphicalWindow {
readonly attribute unsigned long width;
readonly attribute unsigned long height;
attribute Paint currentPaint;
void drawRectangle(double x, double y, double width, double height)<!--
raises(GraphicsException)-->;
void drawText(double x, double y, DOMString text)<!--
raises(GraphicsException)-->;
};</x:codeblock>
<p>
Here, four <a class='dfnref' href='#dfn-interface'>interfaces</a>
are being defined.
The <span class='idltype'>GraphicalWindow</span> interface has two
<a class='dfnref' href='#dfn-read-only'>read only</a> <a class='dfnref' href='#dfn-attribute'>attributes</a>,
one writable attribute, and two <a class='dfnref' href='#dfn-operation'>operations</a>
defined on it. Objects that implement the <span class='idltype'>GraphicalWindow</span> interface
will expose these attributes and operations in a manner appropriate to the
particular language being used.
</p>
<p>
In ECMAScript, the attributes on the IDL interfaces will be exposed as accessor
properties and the operations as <span class='estype'>Function</span>-valued
data properties on a prototype object for all <span class='idltype'>GraphicalWindow</span>
objects; each ECMAScript object that implements <span class='idltype'>GraphicalWindow</span>
will have that prototype object in its prototype chain.
</p>
<!--JAVA
<p>
In Java, there will exist a Java interface that corresponds to the IDL
<span class='idltype'>GraphicalWindow</span> interface. This Java interface
will have methods that correspond to the operations, and getter and setter
methods that correspond to the attributes. Java objects that are considered
to implement the IDL <span class='idltype'>GraphicalWindow</span> interface
will implement the corresponding Java interface.
</p>
-->
<p>
The <a class='xattr' href='#Constructor'>[Constructor]</a> that appears on <span class='idltype'>GraphicalWindow</span>
is an <a class='dfnref' href='#dfn-extended-attribute'>extended attribute</a>.
This extended attribute causes a constructor to exist in ECMAScript implementations,
so that calling <code>new GraphicalWindow()</code> would return a new object
that implemented the interface. <!--JAVA The <a class='xattr' href='#Constructor'>[Constructor]</a>
extended attribute has no effect in the Java language binding, however.-->
</p>
</div>
<div id='idl-names' class='section'>
<h3>Names</h3>
<p>
Every <a class='dfnref' href='#dfn-interface'>interface</a>,
<a class='dfnref' href='#dfn-partial-interface'>partial interface definition</a>,
<a class='dfnref' href='#dfn-dictionary'>dictionary</a>,
<a class='dfnref' href='#dfn-partial-dictionary'>partial dictionary definition</a>,
<a class='dfnref' href='#dfn-enumeration'>enumeration</a>,
<a class='dfnref' href='#dfn-callback-function'>callback function</a> and
<a class='dfnref' href='#dfn-typedef'>typedef</a> (together called <dfn data-export="" data-lt="named definition" id='dfn-named-definition'>named definitions</dfn>)
and every <a class='dfnref' href='#dfn-constant'>constant</a>,
<a class='dfnref' href='#dfn-attribute'>attribute</a>,
and <a class='dfnref' href='#dfn-dictionary-member'>dictionary member</a> has an
<dfn data-export="" id='dfn-identifier'>identifier</dfn>, as do some
<a class='dfnref' href='#dfn-operation'>operations</a>.
The identifier is determined by an
<a class='sym' href='#prod-identifier'>identifier</a> token somewhere
in the declaration:
</p>
<ul>
<li>
For <a class='dfnref' href='#dfn-named-definition'>named definitions</a>,
the <a class='sym' href='#prod-identifier'>identifier</a> token that appears
directly after the <code>interface</code>,
<code>dictionary</code>, <code>enum</code>
or <code>callback</code> keyword
determines the identifier of that definition.
<pre class='syntax'>interface <em>interface-identifier</em> { <i>interface-members…</i> };
partial interface <em>interface-identifier</em> { <i>interface-members…</i> };
dictionary <em>dictionary-identifier</em> { <i>dictionary-members…</i> };
partial dictionary <em>dictionary-identifier</em> { <i>dictionary-members…</i> };
enum <em>enumeration-identifier</em> { <i>enumeration-values…</i> };
callback <em>callback-identifier</em> = <i>callback-signature</i>;</pre>
</li>
<li>
For <a class='dfnref' href='#dfn-attribute'>attributes</a>,
<a class='dfnref' href='#dfn-typedef'>typedefs</a>
and <a class='dfnref' href='#dfn-dictionary-member'>dictionary members</a>,
the final <a class='sym' href='#prod-identifier'>identifier</a> token before the
semicolon at the end of the declaration determines the identifier.
<pre class='syntax'>interface <i>identifier</i> {
attribute <i>type</i> <em>attribute-identifier</em>;
};
typedef <i>type</i> <em>typedef-identifier</em>;
dictionary <i>identifier</i> {
<i>type</i> <em>dictionary-member-identifier</em>;
};</pre>
</li>
<li>
For <a class='dfnref' href='#dfn-constant'>constants</a>,
the <a class='sym' href='#prod-identifier'>identifier</a> token before the
equals sign determines the identifier.
<pre class='syntax'>const <i>type</i> <em>constant-identifier</em> = <i>value</i>;</pre>
</li>
<li>
For <a class='dfnref' href='#dfn-operation'>operations</a>, the
<a class='sym' href='#prod-identifier'>identifier</a> token that appears
after the return type but before the opening parenthesis (that is,
one that is matched as part of the <a class='sym' href='#prod-OptionalIdentifier'>OptionalIdentifier</a>
grammar symbol in an <a class='sym' href='#prod-OperationRest'>OperationRest</a>) determines the identifier of the operation. If
there is no such <a class='sym' href='#prod-identifier'>identifier</a> token,
then the operation does not have an identifier.
<pre class='syntax'><i>return-type</i> <em>operation-identifier</em>(<i>arguments…</i>);</pre>
</li>
</ul>
<div class='note'>
<p>
Operations can have no identifier when they are being used to declare a
<a href='#idl-special-operations'>special kind of operation</a>, such as a getter or setter.
</p>
</div>
<p>
For all of these constructs, the <a class='dfnref' href='#dfn-identifier'>identifier</a>
is the value of the <a class='sym' href='#prod-identifier'>identifier</a> token with any leading
<span class='char'>U+005F LOW LINE ("_")</span> character (underscore) removed.
</p>
<div class='note'>
<p>
A leading <span class='char'>"_"</span> is used to escape an identifier from looking
like a reserved word so that, for example, an interface named “interface” can be
defined. The leading <span class='char'>"_"</span> is dropped to unescape the
identifier.
</p>
</div>
<p>
Operation arguments can take a slightly wider set of identifiers. In an operation
declaration, the identifier of an argument is specified immediately after its
type and is given by either an <a class='sym' href='#prod-identifier'>identifier</a>
token or by one of the keywords that match the <a class='sym' href='#prod-ArgumentNameKeyword'>ArgumentNameKeyword</a>
symbol. If one of these keywords is used, it need not be escaped with a leading
underscore.
</p>
<pre class='syntax'><i>return-type</i> <i>operation-identifier</i>(<i>argument-type</i> <em>argument-identifier</em>, …);</pre>
<?productions grammar ArgumentNameKeyword?>
<p>
If an <a class='sym' href='#prod-identifier'>identifier</a> token is used, then the
<a class='dfnref' href='#dfn-identifier'>identifier</a> of the operation argument
is the value of that token with any leading
<span class='char'>U+005F LOW LINE ("_")</span> character (underscore) removed.
If instead one of the <a class='sym' href='#prod-ArgumentNameKeyword'>ArgumentNameKeyword</a>
keyword token is used, then the <a class='dfnref' href='#dfn-identifier'>identifier</a> of the operation argument
is simply that token.
</p>
<p>
The <a class='dfnref' href='#dfn-identifier'>identifier</a> of any of the abovementioned
IDL constructs <span class='rfc2119'>MUST NOT</span> be “constructor”,
“toString”, “toJSON”,
or begin with a <span class='char'>U+005F LOW LINE ("_")</span> character. These
are known as <dfn data-export="" id='dfn-reserved-identifier'>reserved identifiers</dfn>.
</p>
<div class="note">
<p>Further restrictions on identifier names for particular constructs may be made
in later sections.</p>
</div>
<p>
Within the set of <a class='dfnref' href='#dfn-idl-fragment'>IDL fragments</a>
that a given implementation supports,
the <a class='dfnref' href='#dfn-identifier'>identifier</a> of every
<a class='dfnref' href='#dfn-interface'>interface</a>,
<a class='dfnref' href='#dfn-dictionary'>dictionary</a>,
<a class='dfnref' href='#dfn-enumeration'>enumeration</a>,
<a class='dfnref' href='#dfn-callback-function'>callback function</a> and
<a class='dfnref' href='#dfn-typedef'>typedef</a>
<span class='rfc2119'>MUST NOT</span>
be the same as the identifier of any other
<a class='dfnref' href='#dfn-interface'>interface</a>,
<a class='dfnref' href='#dfn-dictionary'>dictionary</a>,
<a class='dfnref' href='#dfn-enumeration'>enumeration</a>,
<a class='dfnref' href='#dfn-callback-function'>callback function</a> or
<a class='dfnref' href='#dfn-typedef'>typedef</a>.
</p>
<p>
Within an <a class='dfnref' href='#dfn-idl-fragment'>IDL fragment</a>, a reference
to a <a class='dfnref' href='#dfn-definition'>definition</a> need not appear after
the declaration of the referenced definition. References can also be made
across <a class='dfnref' href='#dfn-idl-fragment'>IDL fragments</a>.
</p>
<div class='example'>
<p>Therefore, the following <a class='dfnref' href='#dfn-idl-fragment'>IDL fragment</a> is valid:</p>
<x:codeblock language='idl'>interface B : A {
void f(SequenceOfLongs x);
};
interface A {
};
typedef sequence<long> SequenceOfLongs;</x:codeblock>
</div>
<div class='example'>
<p>
The following <a class='dfnref' href='#dfn-idl-fragment'>IDL fragment</a>
demonstrates how <a class='dfnref' href='#dfn-identifier'>identifiers</a>
are given to definitions and <a class='dfnref' href='#dfn-interface-member'>interface members</a>.
</p>
<x:codeblock language='idl'><span class='comment'>// Typedef identifier: "number"</span>
typedef double number;
<span class='comment'>// Interface identifier: "System"</span>
interface System {
<span class='comment'>// Operation identifier: "createObject"</span>
<span class='comment'>// Operation argument identifier: "interface"</span>
object createObject(DOMString _interface);
<span class='comment'>// Operation argument identifier: "interface"</span>
sequence<object> getObjects(DOMString interface);
<span class='comment'>// Operation has no identifier; it declares a getter.</span>
getter DOMString (DOMString keyName);
};
<span class='comment'>// Interface identifier: "TextField"</span>
interface TextField {
<span class='comment'>// Attribute identifier: "const"</span>
attribute boolean _const;
<span class='comment'>// Attribute identifier: "value"</span>
attribute DOMString? _value;
};</x:codeblock>
<p>
Note that while the second <a class='dfnref' href='#dfn-attribute'>attribute</a>
on the <span class='idltype'>TextField</span> <a class='dfnref' href='#dfn-interface'>interface</a>
need not have been escaped with an underscore (because “value” is
not a keyword in the IDL grammar), it is still unescaped
to obtain the attribute’s <a class='dfnref' href='#dfn-identifier'>identifier</a>.
</p>
</div>
</div>
<div id='idl-interfaces' class='section'>
<h3>Interfaces</h3>
<p>
<a class='dfnref' href='#dfn-idl-fragment'>IDL fragments</a> are used to
describe object oriented systems. In such systems, objects are entities
that have identity and which are encapsulations of state and behavior.
An <dfn data-export="" id='dfn-interface'>interface</dfn> is a definition (matching
<a class='sym' href='#prod-Interface'>Interface</a> or
<span class='sym'>"callback"</span> <a class='sym' href='#prod-Interface'>Interface</a>) that declares some
state and behavior that an object implementing that interface will expose.
</p>
<pre class='syntax'>interface <i>identifier</i> {
<i>interface-members…</i>
};</pre>
<p>
An interface is a specification of a set of
<dfn data-export="" data-lt="interface member" id='dfn-interface-member'>interface members</dfn>
(matching <a class='sym' href='#prod-InterfaceMembers'>InterfaceMembers</a>),
which are the <a class='dfnref' href='#dfn-constant'>constants</a>,
<a class='dfnref' href='#dfn-attribute'>attributes</a>,
<a class='dfnref' href='#dfn-operation'>operations</a> and
other declarations that appear between the braces in the interface declaration.
Attributes describe the state that an object
implementing the interface will expose, and operations describe the
behaviors that can be invoked on the object. Constants declare
named constant values that are exposed as a convenience to users
of objects in the system.
</p>
<p>
Interfaces in Web IDL describe how objects that implement the
interface behave. In bindings for object oriented languages, it is
expected that an object that implements a particular IDL interface
provides ways to inspect and modify the object's state and to
invoke the behavior described by the interface.
</p>
<!--JAVA
<div class='note'>
<p>
In the Java language binding, for example, this is achieved by having the
object implement a Java interface that has methods for reading and
writing attribute values and to invoke an operation.
</p>
</div>
-->
<p>
An interface can be defined to <dfn data-export="" data-dfn-for="interface" id='dfn-inherit'>inherit</dfn> from another interface.
If the identifier of the interface is followed by a
<span class='char'>U+003A COLON (":")</span> character
and an <a class='dfnref' href='#dfn-identifier'>identifier</a>,
then that identifier identifies the inherited interface.
An object that implements an interface that inherits from another
also implements that inherited interface. The object therefore will also
have members that correspond to the interface members from the inherited interface.
</p>
<pre class='syntax'>interface <i>identifier</i> : <em>identifier-of-inherited-interface</em> {
<i>interface-members…</i>
};</pre>
<p>
The order that members appear in has no significance except in the
case of <a href='#idl-overloading'>overloading</a>.
</p>
<p>
Interfaces may specify an interface member that has the same name as
one from an inherited interface. Objects that implement the derived
interface will expose the member on the derived interface. It is
language binding specific whether the overridden member can be
accessed on the object.
</p>
<div class='example'>
<p>
Consider the following two interfaces.
</p>
<x:codeblock language='idl'>interface A {
void f();
void g();
};
interface B : A {
void f();
void g(DOMString x);
};</x:codeblock>
<p>
In the ECMAScript language binding, an instance of <span class='idltype'>B</span>
will have a prototype chain that looks like the following:
</p>
<pre> [Object.prototype: the Object prototype object]
↑
[A.prototype: interface prototype object for A]
↑
[B.prototype: interface prototype object for B]
↑
[instanceOfB]</pre>
<p>
Calling <code>instanceOfB.f()</code> in ECMAScript will invoke the f defined
on <span class='idltype'>B</span>. However, the f from <span class='idltype'>A</span>
can still be invoked on an object that implements <span class='idltype'>B</span> by
calling <code>A.prototype.f.call(instanceOfB)</code>.
</p>
<!--JAVA
<p>
In the Java language binding, the two IDL interfaces will correspond to
the following Java interfaces:
</p>
<x:codeblock language='java'>public interface A {
void f();
void g();
}
public interface B extends A {
void f();
void g(String x);
}</x:codeblock>
<p>
Calling <code>instanceOfB.f()</code> in Java will invoke
the f defined on <span class='idltype'>B</span>. Due to
the way method overriding is defined in Java, there is no
way to call the f defined on <span class='idltype'>A</span>
on an object that implements <span class='idltype'>B</span>.
Since the signature of g is different in <span class='idltype'>A</span>
and <span class='idltype'>B</span>, however, both can be called
with, for example, <code>instanceOfB.g()</code> and
<code>instanceOfB.g("")</code>.
</p>
<p>
In both languages, the f and g from the derived interface
<span class='idltype'>B</span> are always accessible.
</p>
-->
</div>
<p>
The <dfn data-export="" id='dfn-inherited-interfaces'>inherited interfaces</dfn> of
a given interface <var>A</var> is the set of all interfaces that <var>A</var>
inherits from, directly or indirectly. If <var>A</var> does not <a class='dfnref' href='#dfn-inherit'>inherit</a>
from another interface, then the set is empty. Otherwise, the set
includes the interface <var>B</var> that <var>A</var> <a class='dfnref' href='#dfn-inherit'>inherits</a>
from and all of <var>B</var>’s <a class='dfnref' href='#dfn-inherited-interfaces'>inherited interfaces</a>.
</p>
<p>
An interface <span class='rfc2119'>MUST NOT</span> be declared such that
its inheritance hierarchy has a cycle. That is, an interface
<var>A</var> cannot inherit from itself, nor can it inherit from another
interface <var>B</var> that inherits from <var>A</var>, and so on.
</p>
<p>
Note that general multiple inheritance of interfaces is not supported, and
objects also cannot implement arbitrary sets of interfaces.
Objects can be defined to implement a single given interface <var>A</var>,
which means that it also implements all of <var>A</var>’s
<a class='dfnref' href='#dfn-inherited-interfaces'>inherited interfaces</a>. In addition,
an <a href='#idl-implements-statements'>implements statement</a> can be
used to define that objects implementing an interface will always
also implement another interface.
</p>
<p>
Each interface member can be preceded by a list of <a class='dfnref' href='#dfn-extended-attribute'>extended attributes</a> (matching
<a class='sym' href='#prod-ExtendedAttributeList'>ExtendedAttributeList</a>),
which can control how the interface member will be handled in language bindings.
</p>
<pre class='syntax'>interface <i>identifier</i> {
[<em>extended-attributes</em>]
const <i>type</i> <i>identifier</i> = <i>value</i>;
[<em>extended-attributes</em>]
attribute <i>type</i> <i>identifier</i>;
[<em>extended-attributes</em>]
<i>return-type</i> <i>identifier</i>(<i>arguments…</i>);
};</pre>
<p>
A <dfn data-export="" id='dfn-callback-interface'>callback interface</dfn> is
an <a class='dfnref' href='#dfn-interface'>interface</a>
that uses the <code>callback</code> keyword at the start of
its definition. Callback interfaces are ones that can be
implemented by <a class='dfnref' href='#dfn-user-object'>user objects</a>
and not by <a class='dfnref' href='#dfn-platform-object'>platform objects</a>,
as described in <a href='#idl-objects'>section <?sref idl-objects?></a>
<?sdir idl-objects?>.
</p>
<pre class='syntax'>callback interface <i>identifier</i> {
<i>interface-members…</i>
};</pre>
<div class='note'>
<p>See also the similarly named <a class='dfnref' href='#dfn-callback-function'>callback function</a> definition.</p>
</div>
<p>
<a class='dfnref' href='#dfn-callback-interface'>Callback interfaces</a>
<span class='rfc2119'>MUST NOT</span> <a class='dfnref' href='#dfn-inherit'>inherit</a>
from any non-callback interfaces, and non-callback interfaces <span class='rfc2119'>MUST NOT</span>
inherit from any callback interfaces.
Callback interfaces <span class='rfc2119'>MUST NOT</span> have any
<a class='dfnref' href='#dfn-consequential-interfaces'>consequential interfaces</a>.
</p>
<p>
<a class='dfnref' href='#dfn-static-attribute'>Static attributes</a> and
<a class='dfnref' href='#dfn-static-operation'>static operations</a> <span class='rfc2119'>MUST NOT</span>
be defined on a <a class='dfnref' href='#dfn-callback-interface'>callback interface</a>.
</p>
<div class='warning'>
<p>
Specification authors <span class='rfc2119'>SHOULD NOT</span> define
<a class='dfnref' href='#dfn-callback-interface'>callback interfaces</a>
that have only a single <a class='dfnref' href='#dfn-operation'>operation</a>,
unless required to describe the requirements of existing APIs.
Instead, a <a class='dfnref' href='#dfn-callback-function'>callback function</a> <span class='rfc2119'>SHOULD</span> be used.
</p>
<p>
The definition of <span class='idltype'>EventListener</span> as a
<a class='dfnref' href='#dfn-callback-interface'>callback interface</a>
is an example of an existing API that needs to allow
<a class='dfnref' href='#dfn-user-object'>user objects</a> with a
given property (in this case “handleEvent”) to be considered to implement the interface.
For new APIs, and those for which there are no compatibility concerns,
using a <a class='dfnref' href='#dfn-callback-function'>callback function</a> will allow
only a <span class='estype'>Function</span> object (in the ECMAScript
language binding).
</p>
</div>
<div class='ednote'>
<p>
Perhaps this warning shouldn't apply if you are planning to extend the callback
interface in the future. That's probably a good reason to start off with a single
operation callback interface.
</p>
</div>
<div class='ednote'>
<p>
I think we need to support operations not being implemented on a given
user object implementing a callback interface. If specs extending an existing
callback interface, we probably want to be able to avoid calling the
operations that aren't implemented (and having some default behavior instead).
So we should perhaps define a term that means whether the operation is
implemented, which in the ECMAScript binding would correspond to checking
for the property's existence.
</p>
</div>
<div class='note'>
<p>
Specification authors wanting to define APIs that take ECMAScript objects
as “property bag” like function arguments are suggested to use
<a href='#idl-dictionaries'>dictionary types</a> rather than
<a class='dfnref' href='#dfn-callback-interface'>callback interfaces</a>.
</p>
<p>
For example, instead of this:
</p>
<x:codeblock language='idl'>callback interface Options {
attribute DOMString? option1;
attribute DOMString? option2;
attribute long? option3;
};
interface A {
void doTask(DOMString type, Options options);
};</x:codeblock>
<p>
to be used like this:
</p>
<x:codeblock language='es'>var a = getA(); <span class='comment'>// Get an instance of A.</span>
a.doTask("something", { option1: "banana", option3: 100 });</x:codeblock>
<p>
instead write the following:
</p>
<x:codeblock language='idl'>dictionary Options {
DOMString? option1;
DOMString? option2;
long? option3;
};
interface A {
void doTask(DOMString type, Options options);
};</x:codeblock>
</div>
<p>
The IDL for interfaces can be split into multiple parts by using
<dfn data-export="" id='dfn-partial-interface'>partial interface</dfn> definitions
(matching <span class='sym'>"partial"</span> <a class='sym' href='#prod-PartialInterface'>PartialInterface</a>).
The <a class='dfnref' href='#dfn-identifier'>identifier</a> of a partial
interface definition <span class='rfc2119'>MUST</span> be the same
as the identifier of an interface definition. All of
the members that appear on each of the partial interfaces are considered to be
members of the interface itself.
</p>
<pre class='syntax'>interface <em>SomeInterface</em> {
<i>interface-members…</i>
};
partial interface <em>SomeInterface</em> {
<i>interface-members…</i>
};</pre>
<div class='note'>
<p>Partial interface definitions are intended for use as a specification
editorial aide, allowing the definition of an interface to be separated
over more than one section of the document, and sometimes multiple documents.</p>
</div>
<p>
The order of appearance of an <a class='dfnref' href='#dfn-interface'>interface</a>
definition and any of its <a class='dfnref' href='#dfn-partial-interface'>partial interface</a>
definitions does not matter.