HTML 5 (formerly spelled HTML5 ) is a markup language used for structuring and presenting content on the World Wide Web. It is the fifth and current major version of the HTML standard, and subsumes XHTML. It currently exists in two standardized forms: HTML 5.2 Recommendation  by the World Wide Web Consortium (W3C, a broad coalition of organizations), intended primarily for Web content developers; and HTML Living Standard  by WHATWG (a small consortium of four browser vendors), intended primarily for browser developers, though it also exists in an abridged Web developer version.  There are minor conflicts between the two groups' specifications.
HTML 5 was first released in public-facing form on 22 January 2008,  with a major update and "W3C Recommendation" status in October 2014.   Its goals are to improve the language with support for the latest multimedia and other new features; to keep the language both easily readable by humans and consistently understood by computers and devices such as Web browsers, parsers, etc., without XHTML's rigidity; and to remain backward-compatible with older software. HTML 5 is intended to subsume not only HTML 4, but also XHTML 1 and DOM Level 2 HTML ;  the HTML 4 and XHTML specs were announced as superseded by HTML 5.2 on 27 March 2018. 
HTML 5 includes detailed processing models to encourage more interoperable implementations; it extends, improves and rationalizes the markup available for documents, and introduces markup and application programming interfaces (APIs) for complex web applications.  For the same reasons, HTML 5 is also a candidate for cross-platform mobile applications, because it includes features designed with low-powered devices in mind.
Many new syntactic features are included. To natively include and handle multimedia and graphical content, the new <video>, <audio> and <canvas> elements were added, and support for scalable vector graphics ( SVG) content and MathML for mathematical formulas. To enrich the semantic content of documents, new page structure elements such as
<section> , <article>,
<nav> , and
<figure> are added. New attributes are introduced, some elements and attributes have been removed, and others such as
<a /> ,
<cite> , and
<menu> have been changed, redefined, or standardized.
The Web Hypertext Application Technology Working Group (WHATWG) began work on the new standard in 2004. At that time, HTML 4.01 had not been updated since 2000,  and the World Wide Web Consortium (W3C) was focusing future developments on XHTML 2.0. In 2009, the W3C allowed the XHTML 2.0 Working Group's charter to expire and decided not to renew it. 
The Mozilla Foundation and Opera Software presented a position paper at a World Wide Web Consortium (W3C) workshop in June 2004,  focusing on developing technologies that are backward-compatible with existing browsers,  including an initial draft specification of Web Forms 2.0. The workshop concluded with a vote—8 for, 14 against—for continuing work on HTML.  Immediately after the workshop, WHATWG was formed to start work based upon that position paper, and a second draft, Web Applications 1.0, was also announced.  The two specifications were later merged to form HTML 5.  The HTML 5 specification was adopted as the starting point of the work of the new HTML working group of the W3C in 2007.
"Thoughts on Flash"
Last call, candidacy, and recommendation stages
On 14 February 2011, the W3C extended the charter of its HTML Working Group with clear milestones for HTML 5. In May 2011, the working group advanced HTML 5 to "Last Call", an invitation to communities inside and outside W3C to confirm the technical soundness of the specification. The W3C developed a comprehensive test suite to achieve broad interoperability for the full specification by 2014, which was the target date for recommendation.  In January 2011, the WHATWG renamed its "HTML5" specification HTML Living Standard". The W3C nevertheless continued its project to release HTML 5. 
In July 2012, WHATWG and W3C decided on a degree of separation. W3C will continue the HTML 5 specification work, focusing on a single definitive standard, which is considered as a "snapshot" by WHATWG. The WHATWG organization continues its work with HTML 5 as a "living standard". The concept of a living standard is that it is never complete and is always being updated and improved. New features can be added but functionality will not be removed. 
On 16 September 2014, W3C moved HTML 5 to Proposed Recommendation.  On 28 October 2014, HTML 5 was released as a W3C Recommendation,  bringing the specification process to completion.  On 1 November 2016, HTML 5.1 was released as a W3C Recommendation.  On 14 December 2017, HTML 5.2 was released as a W3C Recommendation. 
The combined timelines for HTML 5.0, HTML 5.1 and HTML 5.2:
|Version||First draft||Candidate recommendation||Recommendation|
|HTML 5.0||2007 ||2012||2014|
|HTML 5.2 ||2015||2017||2017|
|HTML 5.3 ||2017||N/A||N/A|
W3C and WHATWG conflict
W3C and WHATWG have been characterized as both working together on the development of HTML 5,  and yet also at cross purposes   ever since the July 2012 split of the W3C work into milestone-based static standards and WHATWG's into a continually updated "living standard". The relationship has been described as "fragile", even a "rift",  and characterized by "squabbling". 
In at least one case, namely the permissible content of the element, the two specifications directly contradict each other (as of July 2018), with the W3C definition being permissive and reflecting traditional use of the element since its introduction,  but WHATWG limiting it to a single defined type of content (the title of the work cited).  This is actually at odds with WHATWG's stated goals of ensuring backward compatibility  and not losing prior functionality. 
The "Introduction" section in the WHATWG spec (edited by Ian "Hixie" Hickson) is critical of W3C, e.g " Note: Although we have asked them to stop doing so, the W3C also republishes some parts of this specification as separate documents." In its "History" subsection it portrays W3C as resistant to Hickson's and WHATWG's original HTML 5 plans, then jumping on the bandwagon belatedly (though Hickson was in control of the W3C HTML 5 spec, too). Regardless, it indicates a major philosophical divide between the organizations: 
For a number of years, both groups then worked together. In 2011, however, the groups came to the conclusion that they had different goals: the W3C wanted to publish a "finished" version of "HTML5", while the WHATWG wanted to continue working on a Living Standard for HTML, continuously maintaining the specification rather than freezing it in a state with known problems, and adding new features as needed to evolve the platform.
Since then, the WHATWG has been working on this specification (amongst others), and the W3C has been copying fixes made by the WHATWG into their fork of the document (which also has other changes).
The "markets" for the two specifications are largely different. The W3C spec is the one that Web developers most often refer to, while the WHATWG version is used by the software development teams of the browser makers (though a version exists for Web content authors, trimmed of the material only of interest to browser coders  ). New features are added to HTML and, often experimentally, to browsers long before they appear in a W3C spec, because they arise in the WHATWG one.  The technology journal Ars Technica observed that "both groups are likely to continue to exist, and both groups will continue to have broad-based industry backing". 
Differences between the two standards
In addition to the contradiction in the element mentioned above, other differences between the two standards include at least the following, as of September 2018:
|Site pagination||Single page version (allows global search of contents)|
|Chapters|| §5 Microdata  |
§9 Communication 
§10 Web workers 
§11 Web storage 
|Global attributes||  : ||  : |
|Chapter Elements of HTML||§4.13 Custom elements |
|Elements|| || |
| § ||§126.96.36.199. Other pragma directives  , based on deprecated WHATWG procedure.|
|§ Sections|| § 188.8.131.52 Sample outlines  |
§ 184.108.40.206 Exposing outlines to users 
|Structured data||Recommends RDFa (code examples    , separate specs   , no special attributes  ).||Recommends Microdata (code examples     , spec chapter  , special attributes  ).|
The following table provides data from the Mozilla Development Network on compatibility with major browsers, as of September 2018, of HTML elements unique to one of the standards:
| ||W3C||All browsers, except Edge|
| ||W3C||None, except Firefox|
| ||WHATWG||All browsers|| "[Since] the HTML outline algorithm is not implemented in any browsers ... the |
| ||WHATWG|| Full support only in Edge and Firefox desktop. |
Partial support in Firefox mobile.
Supported in Opera with user opt-in.
Not supported in other browsers.
| ||WHATWG||All browsers, except Edge and IE||Experimental technology|
Features and APIs
The W3C proposed a greater reliance on modularity as a key part of the plan to make faster progress, meaning identifying specific features, either proposed or already existing in the spec, and advancing them as separate specifications. Some technologies that were originally defined in HTML 5 itself are now defined in separate specifications:
- HTML Working Group – HTML Canvas 2D Context;
- Web Apps Working Group – Web Messaging, Web workers, Web storage, WebSocket, Server-sent events, Web Components (this was not part of HTML 5, though); the Web Applications Working Group was closed in October 2015 and its deliverables transferred to the Web Platform Working Group (WPWG).
- IETF HyBi Working Group – WebSocket Protocol;
- WebRTC Working Group – WebRTC ;
- Web Media Text Tracks Community Group – WebVTT.
After the standardization of the HTML 5 specification in October 2014,  the core vocabulary and features are being extended in four ways.  Likewise, some features that were removed from the original HTML 5 specification have been standardized separately as modules, such as Microdata and Canvas. Technical specifications introduced as HTML 5 extensions such as Polyglot Markup have also been standardized as modules. Some W3C specifications that were originally separate specifications have been adapted as HTML 5 extensions or features, such as SVG. Some features that might have slowed down the standardization of HTML 5 will be standardized as upcoming specifications, instead. HTML 5.1 is expected to be finalized in 2016, and it is currently on the standardization track at the W3C.
HTML 5 introduces elements and attributes that reflect typical usage on modern websites. Some of them are semantic replacements for common uses of generic block (
<div> ) and inline (
<span> ) elements, for example
<nav> (website navigation block),
<footer> (usually referring to bottom of web page or to last lines of HTML code), or
<video> instead of
<object> .    Some deprecated elements from HTML 4.01 have been dropped, including purely presentational elements such as
<center> , whose effects have long been superseded by the more capable Cascading Style Sheets.  There is also a renewed emphasis on the importance of DOM scripting in Web behavior.
The HTML 5 syntax is no longer based on SGML   despite the similarity of its markup. It has, however, been designed to be backward-compatible with common parsing of older versions of HTML. It comes with a new introductory line that looks like an SGML document type declaration,
<!DOCTYPE html> , which triggers the standards-compliant rendering mode.  Since 5 January 2009, HTML 5 also includes Web Forms 2.0 , a previously separate WHATWG specification.  
- Canvas ; 
- Timed Media Playback; 
- Offline; 
- Editable content; 
- Drag and drop ; 
- History; 
- MIME type and protocol handler registration;  
- Microdata ; 
- Web Messaging ; 
- Web Storage – a key-value pair storage framework that provides behaviour similar to cookies but with larger storage capacity and improved API. 
Not all of the above technologies are included in the W3C HTML 5 specification, though they are in the WHATWG HTML specification.  Some related technologies, which are not part of either the W3C HTML 5 or the WHATWG HTML specification, are as follows. The W3C publishes specifications for these separately:
- Geolocation ;
- IndexedDB – an indexed hierarchical key-value store (formerly WebSimpleDB); 
- File  – an API intended to handle file uploads and file manipulation; 
- Directories and System – an API intended to satisfy client-side-storage use cases not well served by databases; 
- File Writer – an API for writing to files from web applications; 
- ClassList. 
- Web cryptography API 
- WebRTC 
- Web SQL Database – a local SQL Database (no longer maintained); 
XHTML 5 (XML-serialized HTML 5)
XML documents must be served with an XML Internet media type (often called " MIME type") such as
application/xml ,  and must conform to strict, well-formed syntax of XML. XHTML 5 is simply XML-serialized HTML 5 data (that is, HTML 5 constrained to XHTML's strict requirements, e.g., not having any unclosed tags), sent with one of XML media types. HTML that has been written to conform to both the HTML and XHTML specifications and which will therefore produce the same DOM tree whether parsed as HTML or XML is known as Polyglot markup 
HTML 5 is designed so that old browsers can safely ignore new HTML 5 constructs.  In contrast to HTML 4.01, the HTML 5 specification gives detailed rules for lexing and parsing, with the intent that compliant browsers will produce the same results when parsing incorrect syntax. Although HTML 5 now defines a consistent behavior for " tag soup " documents, those documents are not regarded as conforming to the HTML 5 standard.
According to a report released on 30 September 2011, 34 of the world's top 100 Web sites were using HTML 5 – the adoption led by search engines and social networks.  Another report released in August 2013 has shown that 153 of the Fortune 500 U.S. companies implemented HTML5 on their corporate websites. 
Since 2014, HTML 5 is at least partially supported by most popular layout engines.
Differences from HTML 4.01 and XHTML 1.x
The following is a cursory list of differences and some specific examples.
- New parsing rules: oriented towards flexible parsing and compatibility; not based on SGML
- Ability to use inline SVG and MathML in
- New elements:
- New types of form controls:
dates and times,
- New attributes:
- Global attributes (that can be applied for every element):
data-*(custom data attributes)
- Deprecated elements will be dropped altogether:
W3C Working Group publishes "HTML5 differences from HTML 4",  which provides a complete outline of additions, removals and changes between HTML 5 and HTML 4.
On 18 January 2011, the W3C introduced a logo to represent the use of or interest in HTML 5. Unlike other badges previously issued by the W3C, it does not imply validity or conformance to a certain standard. As of 1 April 2011, this logo is official. 
When initially presenting it to the public, the W3C announced the HTML 5 logo as a "general-purpose visual identity for a broad set of open web technologies, including HTML 5, CSS, SVG, WOFF, and others".  Some web standard advocates, including The Web Standards Project, criticized that definition of "HTML5" as an umbrella term, pointing out the blurring of terminology and the potential for miscommunication.  Three days later, the W3C responded to community feedback and changed the logo's definition, dropping the enumeration of related technologies.  The W3C then said the logo "represents HTML5, the cornerstone for modern Web applications". 
Digital rights management
Industry players including the BBC, Google, Microsoft, Apple Inc. have been lobbying for the inclusion of Encrypted Media Extensions (EME),      a form of digital rights management (DRM), into the HTML 5 standard. As of the end of 2012 and the beginning of 2013, 27 organisations  including the Free Software Foundation  have started a campaign against including digital rights management in the HTML 5 standard.   However, in late September 2013, the W3C HTML Working Group decided that Encrypted Media Extensions, a form of DRM, was "in scope" and will potentially be included in the HTML 5.1 standard.   WHATWG's "HTML Living Standard" continued to be developed without DRM-enabled proposals. 
The initial enablers for DRM in HTML 5 were Google  and Microsoft.  Supporters also include Adobe.  On 14 May 2014, Mozilla announced plans to support EME in Firefox, the last major browser to avoid DRM.   Calling it "a difficult and uncomfortable step", Andreas Gal of Mozilla explained that future versions of Firefox would remain open source but ship with a sandbox designed to run a content decryption module developed by Adobe.  While promising to "work on alternative solutions", Mozilla's Executive Chair Mitchell Baker stated that a refusal to implement EME would have accomplished little more than convincing many users to switch browsers.  This decision was condemned by Cory Doctorow and the Free Software Foundation.  
- Cache manifest in HTML5
- Comparison of layout engines (HTML5)
- HTML5 in mobile devices
- Polyglot HTML5
- Ian Hickson, Google main editor of HTML5 specs
- David Hyatt, Apple editor of HTML5 specs
- In early W3C recommendations, there was no space between "HTML" and "5" in the name.  This has not been the case since HTML 5.1; the current specification is named HTML 5.2 W3C Recommendation , and "HTML5" does not appear in it.  WHATWG had also used the "HTML5" spelling, but their specification is now named HTML Living Standard , and they have abandoned version numbering.