HTML, an initialism of HyperText Markup Language, is the predominant markup language for web pages. It provides a means to describe the structure of text-based information in a document — by denoting certain text as links, headings, paragraphs, lists, and so on — and to supplement that text with interactive forms, embedded images, and other objects. HTML is written in the form of tags, surrounded by angle brackets. HTML can also describe, to some degree, the appearance and semantics of a document, and can include embedded scripting language code (such as JavaScript) which can affect the behavior of Web browsers and other HTML processors.
HTML is also often used to refer to content of the MIME type text/html or even more broadly as a generic term for HTML whether in its XML-descended form (such as XHTML 1.0 and later) or its form descended directly from SGML (such as HTML 4.01 and earlier).
By convention, html format data files use a file extension .html or .htm.
Contents [hide]
1 History of HTML
1.1 Origins
1.2 First specifications
1.3 Version history of the standard
1.3.1 HTML versions
1.3.2 XHTML versions
2 HTML markup
2.1 Elements
2.2 Attributes
2.3 Character and entity references
2.4 Data types
2.5 The Document Type Declaration
3 Semantic HTML
4 Delivery of HTML
4.1 Publishing HTML with HTTP
4.2 HTML e-mail
4.3 Naming conventions
5 Current flavors of HTML
5.1 Traditional versus XML-based HTML
5.2 Transitional versus Strict
5.3 Frameset versus transitional
5.4 Summary of flavors
6 Hypertext features not in HTML
7 See also
8 References
9 External links
9.1 HTML Markup Validators
9.2 Tutorials
9.3 Standard HTML specifications
9.4 Other specifications
[edit] History of HTML
[edit] 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 and CERN data systems engineer Robert Cailliau each submitted separate proposals for an Internet-based hypertext system providing similar functionality. The following year, they collaborated on a joint proposal, the WorldWideWeb (W3) project,[1] which was accepted by CERN.
[edit] 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.[2][3] It describes 22 elements comprising the initial, relatively simple design of HTML. Thirteen of these elements still exist in HTML 4.[4]
Berners-Lee considered HTML to be, at the time, an application of SGML, but it was not formally defined as such until the mid-1993 publication, by the IETF, of the first proposal for an HTML specification: Berners-Lee and Dan Connolly's "Hypertext Markup Language (HTML)" Internet-Draft, which included an SGML Document Type Definition to define the grammar.[5] 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.[6] 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.[7]
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.[6] Published as Request for Comments 1996, HTML 2.0 included ideas from the HTML and HTML+ drafts.[8] There was no "HTML 1.0"; the 2.0 designation was intended to distinguish the new edition from previous drafts.[9]
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).[7] 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.
[edit] Version history of the standard
HTML
Character encodings
Dynamic HTML
Font family
HTML editor
HTML element
HTML scripting
Layout engine
Quirks mode
Style sheets
Unicode and HTML
W3C
Web colors
XHTML
Comparison of
web browsers
layout engines for
HTML
HTML 5
Non-standard HTML
XHTML
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[edit] HTML versions
July, 1993: Hypertext Markup Language, was published at IETF working draft (that is, not yet a standard).
November, 1995: HTML 2.0 published as IETF Request for Comments:
RFC 1866,
supplemented by RFC 1867 (form-based file upload) that same month,
RFC 1942 (tables) in May 1996,
RFC 1980 (client-side image maps) in August 1996, and
RFC 2070 (internationalization) in January 1997;
Ultimately, all were declared obsolete/historic by RFC 2854 in June 2000.
An HTML 3.0 standard was proposed to the IETF by Dave Raggett and the newly formed W3C in April 1995. It proposed 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 elements.[10] Even though it was designed to be compatible with HTML 2.0, it was too complex at the time to be implemented. Browser vendors opted to support only parts of the proposal, but implemented other markup constructs that they wanted to be incorporated into the standard.[11] When the draft expired in September 1995, work in this direction was discontinued due to lack of browser support. HTML 3.1 was never officially proposed, and the next standard proposal was HTML 3.2 (code-named "Wilbur"), which dropped the majority of the new features in HTML 3.0 and instead adopted many browser-specific element types and attributes that had been created for the Netscape and Mosaic Web browsers.[12]
January 14, 1997: HTML 3.2, published as a W3C Recommendation.
HTML 3.2 was never submitted to the IETF, whose HTML Working Group closed in September 1996;[13] it was instead published as one of the W3C's first "Recommendations" in early 1997. Mathematical support as proposed by HTML 3.0 finally came about years later with a different standard, MathML.
December 18, 1997: HTML 4.0, 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;
HTML 4.0 (initially code-named "Cougar")[12] likewise adopted many browser-specific element types and attributes, but at the same time began to try to "clean up" the standard by marking some of them as deprecated, and suggesting they not be used. Minor editorial revisions to the HTML 4.0 specification were published in 1998 without incrementing the version number and further minor revisions as HTML 4.01.
April 24, 1998: HTML 4.0 was reissued with minor edits without incrementing the version number.
December 24, 1999: HTML 4.01, published as a W3C Recommendation. It offers the same three flavors as HTML 4.0, and its last errata were published May 12, 2001.
HTML 4.01 and ISO/IEC 15445:2000 are the most recent and final versions of HTML.
May 15, 2000: ISO/IEC 15445:2000 ("ISO HTML", based on HTML 4.01 Strict), published as an ISO/IEC international standard.
January 22, 2008: HTML 5, published as a Working Draft by W3C.
[edit] 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. 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.
[edit] HTML 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. HTML Hello World:
Hello HTML
Hello World!
[edit] Elements
See HTML elements for more detailed descriptions.
Elements are the basic structure for HTML markup. Elements have two basic properties: attributes and content. Each attribute and each element's content has certain restrictions that must be followed for an HTML document to be considered valid. An element usually has a start tag (e.g.
) and an end tag (e.g. ). The element's attributes are contained in the start tag and content is located between the tags (e.g.
Content). Some elements, such as
, do not have any content and must not have a closing tag. Listed below are s