html-differences.whatwg.orgHTML Standard Developers Edition

HTML: The Living Standard Developer's Edition — Last Updated 9 April 2020 Table of contents 1 Introduction 1.1 Is this HTML5? 1.2 Background 1.3 Audience 1.4 Scope 1.5 History 1.6 Design notes 1.6.1 Compliance with other specifications 1.6.2 Extensibility 1.7 HTML vs XML syntax 1.8 Structure of this specification 1.8.1 Typographic conventions 1.9 A quick introduction to HTML 1.9.1 Writing secure applications with HTML 1.9.2 Common pitfalls to avoid when using the scripting APIs 1.9.3 How to catch mistakes when writing HTML: validators and conformance checkers 1.10 Conformance requirements for authors 1.10.1 Presentational markup 1.10.2 Syntax errors 1.10.3 Restrictions on content models and on attribute values 1.11 Suggested reading 2 Common infrastructure 2.1 Terminology 2.1.1 Resources 2.1.2 XML compatibility 2.1.3 DOM trees 2.1.4 Scripting 2.1.5 Plugins 2.1.6 Character encodings 2.1.7 Dependencies 2.1.8 Extensibility 2.2 Case-sensitivity and string comparison 2.3 Policy-controlled features 2.4 Common microsyntaxes 2.4.1 Boolean attributes 2.4.2 Keywords and enumerated attributes 2.4.3 Numbers 2.4.3.1 Signed integers 2.4.3.2 Non-negative integers 2.4.3.3 Floating-point numbers 2.4.3.4 Lists of floating-point numbers 2.4.4 Dates and times 2.4.4.1 Months 2.4.4.2 Dates 2.4.4.3 Yearless dates 2.4.4.4 Times 2.4.4.5 Local dates and times 2.4.4.6 Time zones 2.4.4.7 Global dates and times 2.4.4.8 Weeks 2.4.4.9 Durations 2.4.4.10 Vaguer moments in time 2.4.5 Colors 2.4.6 Space-separated tokens 2.4.7 Comma-separated tokens 2.4.8 References 2.4.9 Media queries 2.5 URLs 2.5.1 Terminology 2.5.2 CORS settings attributes 2.5.3 Referrer policy attributes 2.5.4 Nonce attributes 2.5.5 Lazy loading attributes 2.6 Common DOM interfaces 2.6.1 Reflecting content attributes in IDL attributes 2.6.2 Collections 2.6.2.1 The HTMLAllCollection interface 2.6.2.2 The HTMLFormControlsCollection interface 2.6.2.3 The HTMLOptionsCollection interface 2.6.3 The DOMStringList interface 3 Semantics, structure, and APIs of HTML documents 3.1 Documents 3.1.1 The Document object 3.1.2 The DocumentOrShadowRoot interface 3.1.3 Resource metadata management 3.1.4 DOM tree accessors 3.2 Elements 3.2.1 Semantics 3.2.2 Elements in the DOM 3.2.3 Element definitions 3.2.3.1 Attributes 3.2.4 Content models 3.2.4.1 The "nothing" content model 3.2.4.2 Kinds of content 3.2.4.2.1 Metadata content 3.2.4.2.2 Flow content 3.2.4.2.3 Sectioning content 3.2.4.2.4 Heading content 3.2.4.2.5 Phrasing content 3.2.4.2.6 Embedded content 3.2.4.2.7 Interactive content 3.2.4.2.8 Palpable content 3.2.4.2.9 Script-supporting elements 3.2.4.3 Transparent content models 3.2.4.4 Paragraphs 3.2.5 Global attributes 3.2.5.1 The title attribute 3.2.5.2 The lang and xml:lang attributes 3.2.5.3 The translate attribute 3.2.5.4 The dir attribute 3.2.5.5 The style attribute 3.2.5.6 Embedding custom non-visible data with the data-* attributes 3.2.6 The innerText IDL attribute 3.2.7 Requirements relating to the bidirectional algorithm 4 The elements of HTML 4.1 The document element 4.1.1 The html element 4.2 Document metadata 4.2.1 The head element 4.2.2 The title element 4.2.3 The base element 4.2.4 The link element 4.2.4.1 Providing users with a means to follow hyperlinks created using the link element 4.2.5 The meta element 4.2.5.1 Standard metadata names 4.2.5.2 Other metadata names 4.2.5.3 Pragma directives 4.2.5.4 Specifying the document's character encoding 4.2.6 The style element 4.3 Sections 4.3.1 The body element 4.3.2 The article element 4.3.3 The section element 4.3.4 The nav element 4.3.5 The aside element 4.3.6 The h1 , h2 , h3 , h4 , h5 , and h6 elements 4.3.7 The hgroup element 4.3.8 The header element 4.3.9 The footer element 4.3.10 The address element 4.3.11 Headings and sections 4.3.11.1 Creating an outline 4.3.11.2 Sample outlines 4.3.11.3 Exposing outlines to users 4.3.12 Usage summary 4.3.12.1 Article or section? 4.4 Grouping content 4.4.1 The p element 4.4.2 The hr element 4.4.3 The pre element 4.4.4 The blockquote element 4.4.5 The ol element 4.4.6 The ul element 4.4.7 The menu element 4.4.8 The li element 4.4.9 The dl element 4.4.10 The dt element 4.4.11 The dd element 4.4.12 The figure element 4.4.13 The figcaption element 4.4.14 The main element 4.4.15 The div element 4.5 Text-level semantics 4.5.1 The a element 4.5.2 The em element 4.5.3 The strong element 4.5.4 The small element 4.5.5 The s element 4.5.6 The cite element 4.5.7 The q element 4.5.8 The dfn element 4.5.9 The abbr element 4.5.10 The ruby element 4.5.11 The rt element 4.5.12 The rp element 4.5.13 The data element 4.5.14 The time element 4.5.15 The code element 4.5.16 The var element 4.5.17 The samp element 4.5.18 The kbd element 4.5.19 The sub and sup elements 4.5.20 The i element 4.5.21 The b element 4.5.22 The u element 4.5.23 The mark element 4.5.24 The bdi element 4.5.25 The bdo element 4.5.26 The span element 4.5.27 The br element 4.5.28 The wbr element 4.5.29 Usage summary 4.6 Links 4.6.1 Introduction 4.6.2 Links created by a and area elements 4.6.3 API for a and area elements 4.6.4 Downloading resources 4.6.5 Link types 4.6.5.1 Link type " alternate " 4.6.5.2 Link type " author " 4.6.5.3 Link type " bookmark " 4.6.5.4 Link type " canonical " 4.6.5.5 Link type " dns-prefetch " 4.6.5.6 Link type " external " 4.6.5.7 Link type " help " 4.6.5.8 Link type " icon " 4.6.5.9 Link type " license " 4.6.5.10 Link type " modulepreload " 4.6.5.11 Link type " nofollow " 4.6.5.12 Link type " noopener " 4.6.5.13 Link type " noreferrer " 4.6.5.14 Link type " opener " 4.6.5.15 Link type " pingback " 4.6.5.16 Link type " preconnect " 4.6.5.17 Link type " prefetch " 4.6.5.18 Link type " preload " 4.6.5.19 Link type " prerender " 4.6.5.20 Link type " search " 4.6.5.21 Link type " stylesheet " 4.6.5.22 Link type " tag " 4.6.5.23 Sequential link types 4.6.5.23.1 Link type " next " 4.6.5.23.2 Link type " prev " 4.6.5.24 Other link types 4.7 Edits 4.7.1 The ins element 4.7.2 The del element 4.7.3 Attributes common to ins and del elements 4.7.4 Edits and paragraphs 4.7.5 Edits and lists 4.7.6 Edits and tables 4.8 Embedded content 4.8.1 The picture element 4.8.2 The source element 4.8.3 The img element 4.8.4 Images 4.8.4.1 Introduction 4.8.4.1.1 Adaptive images 4.8.4.2 Attributes common to source , img , and link elements 4.8.4.2.1 Srcset attributes 4.8.4.2.2 Sizes attributes 4.8.4.3 Requirements for providing text to act as an alternative for images 4.8.4.3.1 General guidelines 4.8.4.3.2 A link or button containing nothing but the image 4.8.4.3.3 A phrase or paragraph with an alternative graphical representation: charts, diagrams, graphs, maps, illustrations 4.8.4.3.4 A short phrase or label with an alternative graphical representation: icons, logos 4.8.4.3.5 Text that has been rendered to a graphic for typographical effect 4.8.4.3.6 A graphical representation of some of the surrounding text 4.8.4.3.7 Ancillary images 4.8.4.3.8 A purely decorative image that doesn't add any information 4.8.4.3.9 A group of images that form a single larger picture with no links 4.8.4.3.10 A group of images that form a single larger picture with links 4.8.4.3.11 A key part of the content 4.8.4.3.12 An image not intended for the user 4.8.4.3.13 An image in an e-mail or private document intended for a specific person who is known to be able to view images 4.8.5 The iframe element 4.8.6 The embed element 4.8.7 The object element 4.8.8 The param element 4.8.9 The video element 4.8.10 The audio element 4.8.11 The track element 4.8.12 Media elements 4.8.12.1 Error codes 4.8.12.2 Location of the media resource 4.8.12.3 MIME types 4.8.12.4 Network states 4.8.12.5 Loading the media resource 4.8.12.6 Offsets into the media resource 4.8.12.7 Ready states 4.8.12.8 Playing the media resource 4.8.12.9 Seeking 4.8.12.10 Media resources with multiple media tracks 4.8.12.10.1 AudioTrackList and VideoTrackList objects 4.8.12.10.2 Selecting specific audio and video tracks declaratively 4.8.12.1...