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In computing, HyperText Markup Language (HTML) is a markup language designed for the creation of web pages and other information viewable in a browser. The focus of HTML is on the presentation of information—paragraphs, fonts, italics, tables, and so forth—rather than the semantics—what the words mean.
Originally defined as a highly simplified subset of SGML, which is used by organizations with highly complex publishing requirements, HTML is now an international standard (ISO/IEC 15445:2000). The HTML specification is maintained mainly by the World Wide Web Consortium (W3C).
The initial versions of HTML were very tolerant of simple kinds of coding mistakes. The browser commonly made assumptions about intent, and proceeded with the rendering. Over time, the trend has been to create an increasingly strict language syntax. HTML 4.01 is the current version, although the W3C is moving toward replacing it with XHTML, which applies the relentlessly strict checking of XML to the HTML world.
Introduction
HTML is a form of markup that is oriented toward the presentation of single-page text documents with specialized rendering software called an HTML user agent, the most common example of which is a web browser. HTML provides a means by which the document's main content can be annotated with various kinds of metadata and rendering hints. The rendering cues may range from minor text decorations, such as specifying that a certain word be underlined or that an image be inserted, to sophisticated scripts, imagemaps, and form definitions that control web browsers. The metadata may include information about the document's title and author, structural information such as an expression of how the content is segmented into paragraphs, lists, headings, arbitrary divisions, etc., and most importantly, information that allows the document to be linked to other documents. Although most HTML documents contain a main body of text, it is not uncommon to encounter minimal HTML documents that exist only to present visual media in a web browser.
HTML is usually authored in a text editor and stored in a text file with a name usually ending in ".html" or ".htm". Such a file is typically created with the intent that it will be accessed over the World Wide Web, which uses the HTTP network protocol to transfer the files to requesting computers. A request for an HTML document is usually made by a web browser, such as Apple Safari, Mozilla Firefox, or Microsoft Internet Explorer, and upon receipt, the document is rendered and presented to the user. However, HTML can also be transmitted in email messages and rendered by software for email reading, or processed by cellphones that have web browsing capabilities.
Markup There are four kinds of markup elements in HTML: - structural markup that describes the purpose of text. For example,
<h1>Golf</h1> will cause the browser to render "Golf" as a first–level heading (such as how "Markup" above is rendered); - presentational markup that describes the visual appearance of text, regardless of its function. For example,
<b>boldface</b> will render "boldface" in bold text. Presentational markup has since been superseded by CSS and is therefore no longer recommended for general use; - hypertext markup which links parts of the document to other documents. For example,
<a href="http://www.wikipedia.org/">Wikipedia</a> will render the word Wikipedia (http://www.wikipedia.org) as a hyperlink to the specified URL; and - widget elements that create objects, such as buttons and lists.
Note that only presentational markup or Cascading Style Sheets determine how the content within that markup should be presented. The other markup varieties tell the browser what object to render or function to perform.
Separation of style and content Efforts of the web development community have led to a new thinking in the way a web document should be written; XHTML epitomizes this effort. Standards stress using markup which suggests the structure of the document, like headings, paragraphs, block quoted text, and tables, instead of using markup which is written for visual purposes only, like <font>, <b> (bold), and <i> (italics). Such presentational code has been removed from the HTML 4.01 Strict and XHTML specifications in favor of CSS solutions. CSS provides a way to separate the HTML structure from the content's presentation. See separation of style and content.
The document type definition (DTD) All HTML documents should start with a Document Type Definition (or DTD) declaration. For example: <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> This defines a document that conformes to the Strict DTD of HTML 4.01, which is purely structural, leaving formatting to Cascading Style Sheets. Other DTDs, including Loose, Transitional, and Frameset, define different rules for the use of the language.
Version history of the standard - HTML 2.0 (http://www.ietf.org/rfc/rfc1866.txt) — (RFC 1866) approved as a proposed standard September 22, 1995,
- HTML 3.2 (http://www.w3.org/TR/REC-html32) — January 14, 1997,
- HTML 4.0 (http://www.w3.org/TR/REC-html40-971218/) — December 18, 1997,
- HTML 4.01 (http://www.w3.org/TR/html401) (minor fixes) — December 24, 1999,
- ISO/IEC 15445:2000 (http://www.purl.org/NET/ISO+IEC.15445/15445.html) ("ISO HTML", based on HTML 4.01 Strict) — May 15, 2000.
There is no official HTML 1.0 specification because there were multiple informal HTML standards at the time. Work on a successor for HTML, then called 'HTML+', began in late 1993, designed originally to be "A superset of HTML … which will allow a gradual rollover from the previous format of HTML". The first formal specification was therefore given the version number 2.0 in order to distinguish it from these unofficial "standards". Work on HTML+ continued, but this never became a standard.
The HTML 3.0 standard was proposed by the newly formed W3C in March, 1995, and provided many new capabilities such as support for tables, text flow around figures and the display of complex math elements. Even though it was designed to be compatible with HTML 2.0, it was too complex at the time to be implemented, and when the draft expired in September 1995 it was not continued due to lack of browser support. HTML 3.1 was never officially proposed, and the next standard proposal was HTML 3.2, which had dropped the majority of the new features in HTML 3.0 and had instead adopted many browser-specific elements and attributes which had been created for the Netscape and Mosaic web browsers. Support for math as proposed by HTML 3.0 finally came with the different standard MathML.
HTML 4.0 likewise adopted many browser-specific elements and attributes, but at the same time began to try to 'clean up' the standard by marking some of them as 'deprecated'.
There will no longer be any new versions of HTML. However, HTML lives on in XHTML, which is based on XML.
See also
External links - ASCII - ISO 8859-1 Table with HTML Entity Names (http://www.bbsinc.com/iso8859.html)
- W3C's HTML Validator (http://validator.w3.org/)
- HTML/XHTML Validator Project on SourceForge (http://validate.sourceforge.net)
- HTML+ Discussion Document (obsolete) (http://www.w3.org/MarkUp/HTMLPlus/htmlplus_1.html)
- NCSA's Beginner's Guide to HTML (http://archive.ncsa.uiuc.edu/General/Internet/WWW/HTMLPrimer.html)
- The "Head" Part of an HTML Document (http://www.online-web-design-course.com/a/1-11.htm)
- How to use the title property of HTML, by JnanaBase (http://jnana.wikinerds.org/index.php/HTML_title_property)
- Dave's HTML Code Guide (http://www.davesite.com)
- The Visual QuickStart Guide to HTML (http://www.cookwood.com)
Validators - W3C's HTML Validator (http://validator.w3.org/)
- WDG HTML Validator (http://www.htmlhelp.com/tools/validator/)
- Validators and checkers (http://uitest.com/en/cat/analysis/) (Site Check (http://uitest.com/en/check/))
- Validome Validator (http://www.validome.org/)
- HTML/XHTML Validator Project on SourceForge (http://validate.sourceforge.net)
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