HTML, which stands for HyperText Markup Language, is the predominant markup language for web pages. It provides a means to create structured documents by denoting structural semantics for text such as headings, paragraphs, lists etc as well as for links, quotes, and other items.

It allows images and objects to be embedded and can be used to create interactive forms. It is written in the form of HTML elements consisting of "tags" surrounded by angle brackets within the web page content. It can include or can load scripts in languages such as JavaScript which affect the behavior of HTML processors like Web browsers; and Cascading Style Sheets (CSS) to define the appearance and layout of text and other material. The W3C, maintainer of both HTML and CSS standards, encourages the use of CSS over explicit presentational markup.

History

Origins

In 1980, physicist Tim Berners-Lee, who was an independent contractor at CERN, proposed and prototyped ENQUIRE, a system for CERN researchers to use and share documents. In 1989, Berners-Lee wrote a memo proposing an Internet-based hypertext system,[2]. Berners-Lee specified HTML and wrote the browser and server software in the last part of 1990. In that year, Berners-Lee and CERN data systems engineer Robert Cailliau collaborated on a joint request for funding, but the project was not formally adopted by CERN. In his personal notes[3] from 1990 he lists, "some of the many areas in which hypertext is used", and puts an encyclopedia first.

First specifications

The first publicly available description of HTML was a document called HTML Tags, first mentioned on the Internet by Berners-Lee in late 1991. It describes 20 elements comprising the initial, relatively simple design of HTML. Except for the hyperlink tag, these were strongly influenced by SGMLguid, an in-house SGML based documentation format at CERN. Thirteen of these elements still exist in HTML 4.

HTML is a text and image formatting language used by web browsers to dynamically format web pages. Many of the text elements are found in the 1988 ISO technical report TR 9537 Techniques for using SGML, which in turn covers the features of early text formatting languages such as that used by the RUNOFF command developed in the early 1960s for the CTSS (Compatible Time-Sharing System) operating system: these formatting commands were derived from the commands used by typesetters to manually format documents. However the SGML concept of generalized markup is based on elements (nested annotated ranges with attributes) rather than merely point effects, and also the separation of structure and processing: HTML has been progressively moved in this direction with CSS.

Berners-Lee considered HTML to be an application of SGML, and it was formally defined as such by the Internet Engineering Task Force (IETF) with the mid-1993 publication of the first proposal for an HTML specification: "Hypertext Markup Language (HTML)" Internet-Draft by Berners-Lee and Dan Connolly, which included an SGML Document Type Definition to define the grammar. The draft expired after six months, but was notable for its acknowledgment of the NCSA Mosaic browser's custom tag for embedding in-line images, reflecting the IETF's philosophy of basing standards on successful prototypes. Similarly, Dave Raggett's competing Internet-Draft, "HTML+ (Hypertext Markup Format)", from late 1993, suggested standardizing already-implemented features like tables and fill-out forms.

After the HTML and HTML+ drafts expired in early 1994, the IETF created an HTML Working Group, which in 1995 completed "HTML 2.0", the first HTML specification intended to be treated as a standard against which future implementations should be based.[9] Published as Request for Comments 1866, HTML 2.0 included ideas from the HTML and HTML+ drafts. The 2.0 designation was intended to distinguish the new edition from previous drafts.

Further development under the auspices of the IETF was stalled by competing interests. Since 1996, the HTML specifications have been maintained, with input from commercial software vendors, by the World Wide Web Consortium (W3C). However, in 2000, HTML also became an international standard (ISO/IEC 15445:2000). The last HTML specification published by the W3C is the HTML 4.01 Recommendation, published in late 1999. Its issues and errors were last acknowledged by errata published in 2001.

Version history of the standard

HTML version timeline

November 24, 1995

HTML 2.0 was published as IETF RFC 1866. Supplemental RFCs added capabilities:

November 25, 1995:

RFC 1867 (form-based file upload)

May 1996:

RFC 1942 (tables)

August 1996:

RFC 1980 (client-side image maps)

January 1997:

RFC 2070 (internationalization)
In June 2000, all of these were declared obsolete/historic by RFC 2854.

January 1997

HTML 3.2 was published as a W3C Recommendation. It was the first version developed and standardized exclusively by the W3C, as the IETF had closed its HTML Working Group in September 1996.
HTML 3.2 dropped math formulas entirely, reconciled overlap among various proprietary extensions, and adopted most of Netscape's visual markup tags. Netscape's blink element and Microsoft's marquee element were omitted due to a mutual agreement between the two companies. A markup for mathematical formulas similar to that in HTML wasn't standardized until 14 months later in MathML.

December 1997

HTML 4.0 was published as a W3C Recommendation. It offers three "flavors":
Strict, in which deprecated elements are forbidden,
Transitional, in which deprecated elements are allowed,
Frameset, in which mostly only frame related elements are allowed;
Initially code-named "Cougar", HTML 4.0 adopted many browser-specific element types and attributes, but at the same time sought to phase out Netscape's visual markup features by marking them as deprecated in favor of style sheets.

April 1998

HTML 4.0 was reissued with minor edits without incrementing the version number.

December 1999

HTML 4.01 was published as a W3C Recommendation. It offers the same three flavors as HTML 4.0, and its last errata were published May 12, 2001.

May 2000

ISO/IEC 15445:2000 ("ISO HTML", based on HTML 4.01 Strict) was published as an ISO/IEC international standard.
As of mid-2008, HTML 4.01 and ISO/IEC 15445:2000 are the most recent versions of HTML.

Development of the parallel, XML-based language XHTML occupied the W3C's HTML Working Group through the early and mid-2000s.
HTML draft version timeline

October 1991

HTML Tags, an informal CERN document listing twelve HTML tags, was first mentioned in public.
July 1992
First informal draft of the HTML DTD, with six subsequent revisions
November 1992
HTML DTD 1.1 (the first with a version number, based on RCS revisions, which start with 1.1 rather than 1.0), an informal draft

June 1993

Hypertext Markup Language was published by the IETF IIIR Working Group as an Internet-Draft (a rough proposal for a standard). It was replaced by a second version one month later, followed by six further drafts published by IETF itself that finally led to HTML 2.0 in RFC1866

November 1993

HTML+ was published by the IETF as an Internet-Draft and was a competing proposal to the Hypertext Markup Language draft. It expired in May 1994.

April 1995

(authored March 1995)
HTML 3.0 was proposed as a standard to the IETF, but the proposal expired five months later without further action. It included many of the capabilities that were in Raggett's HTML+ proposal, such as support for tables, text flow around figures, and the display of complex mathematical formulas.
W3C began development of its own Arena browser for testing support for HTML 3 and Cascading Style Sheets, but HTML 3.0 did not succeed for several reasons.

The draft was considered very large at 150 pages and the pace of browser development, as well as the number of interested parties, had outstripped the resources of the IETF.[13] Browser vendors, including Microsoft and Netscape at the time, chose to implement different subsets of HTML 3's draft features as well as to introduce their own extensions to it. (See Browser wars) These included extensions to control stylistic aspects of documents, contrary to the "belief [of the academic engineering community] that such things as text color, background texture, font size and font face were definitely outside the scope of a language when their only intent was to specify how a document would be organized." Dave Raggett, who has been a W3C Fellow for many years has commented for example, "To a certain extent, Microsoft built its business on the Web by extending HTML features."

January 2008

HTML 5 was published as a Working Draft by the W3C.
Although its syntax closely resembles that of SGML, HTML 5 has abandoned any attempt to be an SGML application, and has explicitly defined its own "html" serialization, in addition to an alternative XML-based XHTML 5 serialization.
XHTML versions
Main article: XHTML
XHTML is a separate language that began as a reformulation of HTML 4.01 using XML 1.0. It continues to be developed:

XHTML 1.0, published January 26, 2000 as a W3C Recommendation, later revised and republished August 1, 2002. It offers the same three flavors as HTML 4.0 and 4.01, reformulated in XML, with minor restrictions.
XHTML 1.1, published May 31, 2001 as a W3C Recommendation. It is based on XHTML 1.0 Strict, but includes minor changes, can be customized, and is reformulated using modules from Modularization of XHTML, which was published April 10, 2001 as a W3C Recommendation.
XHTML 2.0, is still a W3C Working Draft. W3C announched that the XHTML 2 group will stop work by end of 2009[29]. There will be no XHTML 2.0 standard. XHTML 2.0 is incompatible with XHTML 1.x and, therefore, would be more accurate to characterize as an XHTML-inspired new language than an update to XHTML 1.x.
XHTML 5, which is an update to XHTML 1.x, is being defined alongside HTML 5 in the HTML 5 draft.

Markup

HTML markup consists of several key components, including elements (and their attributes), character-based data types, and character references and entity references. Another important component is the document type declaration, which specifies the Document Type Definition. As of HTML 5, no Document Type Definition will need to be specified, and will only determine the layout mode[4].

The Hello world program, a common computer program employed for comparing programming languages, scripting languages, and markup languages is made of 9 lines of code in HTML, albeit Newlines are optional:

This Document Type Declaration is for HTML 5.

If the declaration is not included, most browsers will render using "quirks mode."

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