HTML (HyperText Markup Language)
File name extension	. A filename extension is a suffix to the name of a Computer file applied to indicate the encoding convention ( File format) of its contents html, . htm
Internet media type	text/html
Type code	TEXT
Uniform Type Identifier	public. An Internet media type, originally called a MIME type after MIME and sometimes a Content-type after the name of a header in several protocols whose value A type code is the only mechanism used in pre- Mac OS X versions of the Macintosh Operating system to denote a file's format, in a manner similar A Uniform Type Identifier ( UTI) is a string defined by Apple Inc html
Developed by	World Wide Web Consortium
Type of format	Markup language
Extended from	SGML
Extended to	XHTML

HTML, an initialism of HyperText Markup Language, is the predominant markup language for web pages. A markup language is an Artificial language using a set of annotations to text that give instructions regarding the structure of text or how it is to be displayed The Standard Generalized Markup Language ( ISO 88791986 SGML) is an ISO Standard Metalanguage in which one can define Markup languages The Extensible Hypertext Markup Language, or XHTML, is a Acronyms, initialisms, and alphabetisms are Abbreviations that are formed using the initial components in a phrase or name A markup language is an Artificial language using a set of annotations to text that give instructions regarding the structure of text or how it is to be displayed A web page or webpage is a resource of information that is suitable for the World Wide Web and can be accessed through a Web browser. 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. Brackets are Punctuation marks used in pairs to set apart or interject text within other text 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. Semantics is the study of meaning in communication The word derives from Greek σημαντικός ( semantikos) "significant" from "Scripting" redirects here For other uses see Script. A web browser is a software application which enables a user to display and interact with text images videos music games and other information typically located on a

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. An Internet media type, originally called a MIME type after MIME and sometimes a Content-type after the name of a header in several protocols whose value Don't change "Extensible" The Extensible Hypertext Markup Language, or XHTML, is a 0 and later) or its form descended directly from SGML (such as HTML 4. The Standard Generalized Markup Language ( ISO 88791986 SGML) is an ISO Standard Metalanguage in which one can define Markup languages 01 and earlier).

By convention, HTML format data files use a file extension . html or . htm.

History of HTML

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. Sir Timothy John Berners-Lee OM KBE FRS FREng FRSA (born 8 June 1955 is an English computer scientist who is credited The European Organization for Nuclear Research (Organisation Européenne pour la Recherche Nucléaire known as CERN ENQUIRE was an early project (in the second half of 1980 of Tim Berners-Lee, who went on to create the World Wide Web in 1989 In 1989, Berners-Lee and CERN data systems engineer Robert Cailliau each submitted separate proposals for an Internet-based hypertext system providing similar functionality. Robert Cailliau (born 26 January 1947) is a Belgian Computer scientist who together with Sir Tim Berners-Lee, developed The Internet is a global system of interconnected Computer networks The following year, they collaborated on a joint proposal, the WorldWideWeb (W3) project,^[1] which was accepted by CERN.

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. The Standard Generalized Markup Language ( ISO 88791986 SGML) is an ISO Standard Metalanguage in which one can define Markup languages Dan Connolly received a BS in Computer Science from the University of Texas at Austin in 1990 Document Type Definition ( DTD) is one of several SGML and XML schema languages and is also the term used to describe a document or portion thereof that ^[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. Mosaic is the browser which popularized the World Wide Web. It was also a browser for earlier concepts such as Ftp, Usenet, and Gopher ^[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. In Computer network Engineering, a Request for Comments (RFC is a Memorandum published by the Internet Engineering Task Force (IETF describing 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 International Electrotechnical Commission ( IEC) is a not-for-profit, non-governmental international Standards organization that prepares and publishes 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 versions

July, 1993: Hypertext Markup Language, was published at IETF working draft (that is, not yet a standard). HTML has been in use since 1991, but HTML 40 (December 1997 was the first standardized version where international characters were given reasonably complete treatment Dynamic HTML, or DHTML, is a collection of technologies used together to create interactive and animated Web sites by using a combination of a static Markup In HTML and XHTML, a font face or font family is the typeface that is applied to some text An HTML editor is a software application for creating Web pages Although the HTML markup of a web page can be written with any Text editor, specialized In Computing, an HTML element indicates structure in an HTML document and a way of hierarchically arranging content HTML Series The W3C HTML standard includes support for Client-side scripting. A layout engine, or rendering engine, is software that takes marked up content (such as HTML, XML, image files etc Quirks mode refers to a technique used by some Web browsers for the sake of maintaining backwards compatibility with Web pages designed for older browsers instead of Web style sheets are a form of Separation of presentation and content for Web design in which the markup (i Web pages authored using hypertext markup language ( HTML) may contain multilingual text represented with the Unicode universal character set. Web colors are Colors used in designing web pages and the methods for describing and specifying those colors The Extensible Hypertext Markup Language, or XHTML, is a The following tables compare general and technical information for a number of Web browsers Please see the individual products' articles for further information The following tables compare HTML compatibility and support for a number of Layout engines Please see the individual products' articles for further information The following tables compare support of HTML 5 differences from HTML 4 for a number of Layout engines The specification is still a working draft not The following tables compare deprecated and proprietary HTML tags and attributes compatibility and support for a number of Layout engines Please see the individual products' articles for The following tables compare XHTML compatibility and support for a number of Layout engines Please see the individual products' articles for further information

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. In Computer network Engineering, a Request for Comments (RFC is a Memorandum published by the Internet Engineering Task Force (IETF describing In Computing, Internationalization and localization (also spelled internationalisation and localisation, see spelling differences) are means of adapting

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. Netscape Navigator and Netscape are the names for the proprietary Web browser popular in the 1990s and the Flagship product of the Netscape Mosaic is the browser which popularized the World Wide Web. It was also a browser for earlier concepts such as Ftp, Usenet, and Gopher ^[12]

January 14, 1997: HTML 3.2, published as a W3C Recommendation. Events 1129 - Formal approval of the Order of the Templar at the Council of Troyes. Year 1997 ( MCMXCVII) was a Common year starting on Wednesday (link will display full 1997 Gregorian calendar A W3C Recommendation is the final stage of a Ratification process of the World Wide Web Consortium (W3C working group concerning the Standard.

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. Mathematical Markup Language ( MathML) is an application of XML for describing mathematical notations and capturing both its structure and content

December 18, 1997: HTML 4.0, published as a W3C Recommendation. Events 218 BC - Second Punic War: Battle of the Trebia - Hannibal 's Carthaginian forces defeat those of the Year 1997 ( MCMXCVII) was a Common year starting on Wednesday (link will display full 1997 Gregorian calendar 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. On a Web page, framing means that a Website can be organized into frames. 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. In Computer software standards and documentation the term deprecation is applied to Software features that are superseded and should be avoided 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. Events 1479 BC - Thutmose III ascends to the throne of Egypt, although power effectively shifts to Hatshepsut (according to Year 1998 ( MCMXCVIII) was a Common year starting on Thursday (link will display full 1998 Gregorian calendar)

December 24, 1999: HTML 4.01, published as a W3C Recommendation. Events 563 - The Byzantine church Hagia Sophia in Constantinople is dedicated for the second time after being destroyed by Earthquakes Year 1999 ( MCMXCIX) was a Common year starting on Friday (link will display full 1999 Gregorian calendar) It offers the same three flavors as HTML 4. 0, and its last errata were published May 12, 2001. Events 1191 - Richard I of England marries Berengaria of Navarre. Year 2001 ( MMI) was a Common year starting on Monday according to the Gregorian calendar.

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. Events 1252 - Pope Innocent IV issues the Papal bull Ad exstirpanda, which authorizes but also limits the 2000 ( MM) was a Leap year that started on Saturday of the Common Era, in accordance with the Gregorian calendar. 01 Strict), published as an ISO/IEC international standard.

January 22, 2008: HTML 5, published as a Working Draft by W3C. Events 565 - Eutychius is deposed as Patriarch of Constantinople by John Scholasticus. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common

XHTML versions

Main article: XHTML

XHTML is a separate language that began as a reformulation of HTML 4. The Extensible Hypertext Markup Language, or XHTML, is a 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. Events 1340 - King Edward III of England is declared King of France. 2000 ( MM) was a Leap year that started on Saturday of the Common Era, in accordance with the Gregorian calendar. Events 30 BC - Octavian (later known as Augustus enters Alexandria, Egypt, bringing it under the control of the Roman See also 2002 (disambiguation Year 2002 ( MMII) was a Common year starting on Tuesday of the Gregorian calendar. 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. Events 1279 BC - Rameses II (The Great (19th dynasty becomes pharaoh of Ancient Egypt. Year 2001 ( MMI) was a Common year starting on Monday according to the Gregorian calendar. 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. Events 879 - Louis III becomes King of the Western Franks. 1407 - the lama Year 2001 ( MMI) was a Common year starting on Monday according to the Gregorian calendar.
• 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. HTML 5 ( HyperText Markup Language 5) is planned to be the fifth major revision of the core language of the World Wide Web, HTML.

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:

<html>
<head>
<title>Hello HTML</title>
</head>
<body>
<span>Hello World!</span>
</body>
</html>

Elements

See HTML elements for more detailed descriptions. In Computing, an HTML element indicates structure in an HTML document and a way of hierarchically arranging content

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. <element-name>) and an end tag (e. g. </element-name>). The element's attributes are contained in the start tag and content is located between the tags (e. g. <element-name attribute="value">Content</element-name>). Some elements, such as <br>, do not have any content and must not have a closing tag. Listed below are several types of markup elements used in HTML.

Structural markup describes the purpose of text. For example, <h2>Golf</h2> establishes "Golf" as a second-level heading, which would be rendered in a browser in a manner similar to the "HTML markup" title at the start of this section. Structural markup does not denote any specific rendering, but most Web browsers have standardized on how elements should be formatted. Text may be further styled with Cascading Style Sheets (CSS).

Presentational markup describes the appearance of the text, regardless of its function. For example <b>boldface</b> indicates that visual output devices should render "boldface" in bold text, but gives no indication what devices which are unable to do this (such as aural devices that read the text aloud) should do. In the case of both <b>bold</b> and <i>italic</i>, there are elements which usually have an equivalent visual rendering but are more semantic in nature, namely <strong>strong emphasis</strong> and <em>emphasis</em> respectively. It is easier to see how an aural user agent should interpret the latter two elements. However, they are not equivalent to their presentational counterparts: it would be undesirable for a screen-reader to emphasize the name of a book, for instance, but on a screen such a name would be italicized. Most presentational markup elements have become deprecated under the HTML 4. In Computer software standards and documentation the term deprecation is applied to Software features that are superseded and should be avoided 0 specification, in favor of CSS based style design.

Hypertext markup links parts of the document to other documents. HTML up through version XHTML 1. The Extensible Hypertext Markup Language, or XHTML, is a 1 requires the use of an anchor element to create a hyperlink in the flow of text: <a>Wikipedia</a>. However, the href attribute must also be set to a valid URL so for example the HTML code, <a href="http://en. Uniform Resource Locator is an URI which also specifies where the identified resource is available and the protocol for retrieving it wikipedia. org/">Wikipedia</a>, will render the word "Wikipedia" as a hyperlink. In computing a hyperlink is a Reference or Navigation element in a Document to another Section of the same document or to another To link on an image, the anchor tag use the following syntax: <a href="url"><img src="image. gif" /></a>

Attributes

Most of the attributes of an element are name-value pairs, separated by "=", and written within the start tag of an element, after the element's name. The value may be enclosed in single or double quotes, although values consisting of certain characters can be left unquoted in HTML (but not XHTML). ^[14][15] Leaving attribute values unquoted is considered unsafe. ^[16] In contrast with name-value pair attributes, there are some attributes that affect the element simply by their presence in the start tag of the element^[17] (like the ismap attribute for the img element^[18]).

Most elements can take any of several common attributes:

• The id attribute provides a document-wide unique identifier for an element. This can be used by stylesheets to provide presentational properties, by browsers to focus attention on the specific element, or by scripts to alter the contents or presentation of an element.

• The class attribute provides a way of classifying similar elements for presentation purposes. For example, an HTML document might use the designation class="notation" to indicate that all elements with this class value are subordinate to the main text of the document. Such elements might be gathered together and presented as footnotes on a page instead of appearing in the place where they occur in the HTML source.

• An author may use the style non-attributal codes presentational properties to a particular element. It is considered better practice to use an element’s son- id page and select the element with a stylesheet, though sometimes this can be too cumbersome for a simple ad hoc application of styled properties.

• The title attribute is used to attach subtextual explanation to an element. In most browsers this attribute is displayed as what is often referred to as a tooltip. The tooltip is a common Graphical user interface element It is used in conjunction with a cursor, usually a mouse pointer

The generic inline element span can be used to demonstrate these various attributes:

<span id="anId" class="aClass" style="color:blue;" title="Hypertext Markup Language">HTML</span>

This example displays as HTML; in most browsers, pointing the cursor at the abbreviation should display the title text "Hypertext Markup Language. "

Most elements also take the language-related attributes lang and dir.

Character and entity references

As of version 4. 0, HTML defines a set of 252 character entity references and a set of 1,114,050 numeric character references, both of which allow individual characters to be written via simple markup, rather than literally. In SGML, HTML and XML documents the logical constructs known as character data and attribute values consist of sequences of characters In the Markup languages SGML, HTML, XHTML and XML, a character entity reference is a reference to a particular kind of named A numeric character reference (NCR is a common markup construct used in SGML and other SGML-based markup languages such as HTML and XML. A literal character and its markup counterpart are considered equivalent and are rendered identically.

The ability to "escape" characters in this way allows for the characters < and & (when written as < and &, respectively) to be interpreted as character data, rather than markup. For example, a literal < normally indicates the start of a tag, and & normally indicates the start of a character entity reference or numeric character reference; writing it as & or & or & allows & to be included in the content of elements or the values of attributes. The double-quote character ("), when used to quote an attribute value, must also be escaped as " or " or " when it appears within the attribute value itself. The single-quote character ('), when used to quote an attribute value, must also be escaped as ' or ' (should NOT be escaped as ' except in XHTML documents) when it appears within the attribute value itself. However, since document authors often overlook the need to escape these characters, browsers tend to be very forgiving, treating them as markup only when subsequent text appears to confirm that intent.

Escaping also allows for characters that are not easily typed or that aren't even available in the document's character encoding to be represented within the element and attribute content. A character encoding consists of a code that pairs a sequence of characters from a given character set (sometimes incorrectly referred to as Code page For example, the acute-accented e (é), a character typically found only on Western European keyboards, can be written in any HTML document as the entity reference é or as the numeric references é or é. The characters comprising those references (that is, the &, the ;, the letters in eacute, and so on) are available on all keyboards and are supported in all character encodings, whereas the literal é is not.

Data types

HTML defines several data types for element content, such as script data and stylesheet data, and a plethora of types for attribute values, including IDs, names, URIs, numbers, units of length, languages, media descriptors, colors, character encodings, dates and times, and so on. A data type in Programming languages is an attribute of a datum which tells the computer (and the programmer something about the kind of datum it is All of these data types are specializations of character data.

The Document Type Declaration

In order to enable Document Type Definition (DTD)-based validation with SGML tools and in order to avoid the quirks mode in browsers, HTML documents can start with a Document Type Declaration (informally, a "DOCTYPE"). Document Type Definition ( DTD) is one of several SGML and XML schema languages and is also the term used to describe a document or portion thereof that Quirks mode refers to a technique used by some Web browsers for the sake of maintaining backwards compatibility with Web pages designed for older browsers instead of A Document Type Declaration, or DOCTYPE, is an instruction that associates a particular SGML or XML document (for example a Webpage) with a The DTD to which the DOCTYPE refers contains machine-readable grammar specifying the permitted and prohibited content for a document conforming to such a DTD. Browsers do not necessarily read the DTD, however. The most popular graphical browsers use DOCTYPE declarations (or the lack thereof) and other data at the beginning of sources to determine which rendering mode to use.

For example:

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4. 01//EN" "http://www. w3. org/TR/html4/strict. dtd">

This declaration references the Strict DTD of HTML 4. 01, which does not have presentational elements like <font>, leaving formatting to Cascading Style Sheets and the span and div tags. SGML-based validators read the DTD in order to properly parse the document and to perform validation. In modern browsers, the HTML 4. 01 Strict doctype activates standards layout mode for CSS as opposed to quirks mode. Quirks mode refers to a technique used by some Web browsers for the sake of maintaining backwards compatibility with Web pages designed for older browsers instead of

In addition, HTML 4. 01 provides Transitional and Frameset DTDs. The Transitional DTD was intended to gradually phase in the changes made in the Strict DTD, while the Frameset DTD was intended for those documents which contained frames.

Semantic HTML

There is no official specification called "Semantic HTML", though the strict flavors of HTML discussed below are a push in that direction. Rather, semantic HTML refers to an objective and a practice to create documents with HTML that contain only the author's intended meaning, without any reference to how this meaning is presented or conveyed. A classic example is the distinction between the emphasis element (<em>) and the italics element (<i>). Often the emphasis element is displayed in italics, so the presentation is typically the same. However, emphasizing something is different from listing the title of a book, for example, which may also be displayed in italics. In purely semantic HTML, a book title would use a different element than emphasized text uses (for example a <span>), because they are meaningfully different things.

The goal of semantic HTML requires two things of authors:

1. To avoid the use of presentational markup (elements, attributes, and other entities).
2. To use available markup to differentiate the meanings of phrases and structure in the document. So for example, the book title from above would need to have its own element and class specified, such as <cite class="booktitle">The Grapes of Wrath</cite>. Here, the <cite> element is used because it most closely matches the meaning of this phrase in the text. However, the <cite> element is not specific enough to this task, since we mean to cite specifically a book title as opposed to a newspaper article or an academic journal.

Semantic HTML also requires complementary specifications and software compliance with these specifications. Primarily, the development and proliferation of CSS has led to increasing support for semantic HTML, because CSS provides designers with a rich language to alter the presentation of semantic-only documents. With the development of CSS, the need to include presentational properties in a document has virtually disappeared. With the advent and refinement of CSS and the increasing support for it in Web browsers, subsequent editions of HTML increasingly stress only using markup that suggests the semantic structure and phrasing of the document, like headings, paragraphs, quotes, and lists, instead of using markup which is written for visual purposes only, like <font>, <b> (bold), and <i> (italics). Some of these elements are not permitted in certain varieties of HTML, like HTML 4. 01 Strict. CSS provides a way to separate document semantics from the content's presentation, by keeping everything relevant to presentation defined in a CSS file. See separation of style and content. Separation of presentation and content (or "separate content from presentation") is common Idiom, a Design philosophy, and a methodology applied

Semantic HTML offers many advantages. First, it ensures consistency in style across elements that have the same meaning. Every heading, every quotation, every similar element receives the same presentation properties.

Second, semantic HTML frees authors from the need to concern themselves with presentation details. When writing the number two, for example, should it be written out in words ("two"), or should it be written as a numeral (2)? A semantic markup might enter something like <number>2</number> and leave presentation details to the stylesheet designers. Similarly, an author might wonder where to break out quotations into separate indented blocks of text: with purely semantic HTML, such details would be left up to stylesheet designers. Authors would simply indicate quotations when they occur in the text, and not concern themselves with presentation.

A third advantage is device independence and repurposing of documents. A semantic HTML document can be paired with any number of stylesheets to provide output to computer screens (through Web browsers), high-resolution printers, handheld devices, aural browsers or braille devices for those with visual impairments, and so on. To accomplish this, nothing needs to be changed in a well-coded semantic HTML document. Readily available stylesheets make this a simple matter of pairing a semantic HTML document with the appropriate stylesheets. (Of course, the stylesheet's selectors need to match the appropriate properties in the HTML document. )

Some aspects of authoring documents make separating semantics from style (in other words, meaning from presentation) difficult. Some elements are hybrids, using presentation in their very meaning. For example, a table displays content in a tabular form. Often such content conveys the meaning only when presented in this way. Repurposing a table for an aural device typically involves somehow presenting the table as an inherently visual element in an audible form. On the other hand, we frequently present lyrical songs—something inherently meant for audible presentation—and instead present them in textual form on a Web page. For these types of elements, the meaning is not so easily separated from their presentation. However, for a great many of the elements used and meanings conveyed in HTML, the translation is relatively smooth.

Delivery of HTML

HTML documents can be delivered by the same means as any other computer file; however, they are most often delivered in one of two forms: over HTTP servers and through e-mail. Hypertext Transfer Protocol ( HTTP) is a Communications protocol for the transfer of information on the Internet.

Publishing HTML with HTTP

The World Wide Web is composed primarily of HTML documents transmitted from a Web server to a Web browser using the Hypertext Transfer Protocol (HTTP). The World Wide Web (commonly shortened to the Web) is a system of interlinked Hypertext documents accessed via the Internet. The term web server can mean one of two things A Computer program that is responsible for accepting HTTP requests from web clients which are Hypertext Transfer Protocol ( HTTP) is a Communications protocol for the transfer of information on the Internet. However, HTTP can be used to serve images, sound, and other content in addition to HTML. To allow the Web browser to know how to handle the document it received, an indication of the file format of the document must be transmitted along with the document. A file format is a particular way to encode information for storage in a Computer file. This vital metadata includes the MIME type (text/html for HTML 4. Metadata ( meta data, or sometimes metainformation) is "data about data" of any sort in any media Multipurpose Internet Mail Extensions ( MIME) is an Internet standard that extends the format of e-mail to support text in Character 01 and earlier, application/xhtml+xml for XHTML 1. 0 and later) and the character encoding (see Character encodings in HTML). HTML has been in use since 1991, but HTML 40 (December 1997 was the first standardized version where international characters were given reasonably complete treatment

In modern browsers, the MIME type that is sent with the HTML document affects how the document is interpreted. A document sent with an XHTML MIME type, or served as application/xhtml+xml, is expected to be well-formed XML, and a syntax error causes the browser to fail to render the document. Don't change "Extensible" The same document sent with an HTML MIME type, or served as text/html, might be displayed successfully, since Web browsers are more lenient with HTML. However, XHTML parsed in this way is not considered either proper XHTML or HTML, but so-called tag soup. In Web development, tag soup refers to HTML code written for a Web page without regard for the rules of HTML structure and semantics

If the MIME type is not recognized as HTML, the Web browser should not attempt to render the document as HTML, even if the document is prefaced with a correct Document Type Declaration. Nevertheless, some Web browsers do examine the contents or URL of the document and attempt to infer the file type, despite this being forbidden by the HTTP 1. 1 specification.

HTML e-mail

Main article: HTML e-mail

Most graphical e-mail clients allow the use of a subset of HTML (often ill-defined) to provide formatting and semantic markup capabilities not available with plain text, like emphasized text, block quotations for replies, and diagrams or mathematical formulas that could not easily be described otherwise. HTML e-mail is the use of a Subset of HTML (often ill-defined to provide formatting and semantic markup capabilities in E-mail that are not Electronic mail, often abbreviated to e-mail, email, or originally eMail, is a Store-and-forward method of writing sending receiving The Semantic Web is an evolving extension of the World Wide Web in which the Semantics of information and services on the web is defined making it possible for the In Computing, plain text is a term used for an ordinary "unformatted" sequential file readable as textual material without much processing Many of these clients include both a GUI editor for composing HTML e-mail messages and a rendering engine for displaying received HTML messages. Use of HTML in e-mail is controversial because of compatibility issues, because it can be used in phishing/privacy attacks, because it can confuse spam filters, and because the message size is larger than plain text. In the field of computer security phishing is the Criminally Fraudulent process of attempting to acquire sensitive information such as usernames Passwords E-mail spam, also known as "bulk e-mail" or "junk e-mail" is a subset of spam that involves nearly identical messages sent to numerous recipients by

Naming conventions

The most common filename extension for files containing HTML is . A filename extension is a suffix to the name of a Computer file applied to indicate the encoding convention ( File format) of its contents A computer file is a block of Arbitrary Information, or resource for storing information which is available to a Computer program and is usually html. A common abbreviation of this is . htm; it originates from older operating systems and file systems, such as the DOS versions from the 80s and early 90s and FAT, which limit file extensions to three letters. DOS, short for "Disk Operating System" is a shorthand term for several closely related Operating systems that dominated the IBM PC compatible market Templateinfobox filesystem whilst covering all 3 file systems please make any style changes to both at the same time Both forms are widely supported by browsers.

Current flavors of HTML

Since its inception, HTML and its associated protocols gained acceptance relatively quickly. However, no clear standards existed in the early years of the language. Though its creators originally conceived of HTML as a semantic language devoid of presentation details, practical uses pushed many presentational elements and attributes into the language, driven largely by the various browser vendors. The latest standards surrounding HTML reflect efforts to overcome the sometimes chaotic development of the language and to create a rational foundation for building both meaningful and well-presented documents. To return HTML to its role as a semantic language, the W3C has developed style languages such as CSS and XSL to shoulder the burden of presentation. In Computing, the Extensible Stylesheet Language ( XSL) a family of Transformation languages allows one to describe how to format or transform files encoded In conjunction, the HTML specification has slowly reined in the presentational elements.

There are two axes differentiating various flavors of HTML as currently specified: SGML-based HTML versus XML-based HTML (referred to as XHTML) on the one axis, and strict versus transitional (loose) versus frameset on the other axis.

Traditional versus XML-based HTML

One difference in the latest HTML specifications lies in the distinction between the SGML-based specification and the XML-based specification. The XML-based specification is usually called XHTML to distinguish it clearly from the more traditional definition; however, the root element name continues to be 'html' even in the XHTML-specified HTML. The W3C intended XHTML 1. 0 to be identical to HTML 4. 01 except where limitations of XML over the more complex SGML require workarounds. Because XHTML and HTML are closely related, they are sometimes documented in parallel. In such circumstances, some authors conflate the two names as (X)HTML or X(HTML). ^[19]

Like HTML 4. 01, XHTML 1. 0 has three sub-specifications: strict, loose, and frameset.

Aside from the different opening declarations for a document, the differences between an HTML 4. 01 and XHTML 1. 0 document—in each of the corresponding DTDs—are largely syntactic. The underlying syntax of HTML allows many shortcuts that XHTML does not, such as elements with optional opening or closing tags, and even EMPTY elements which must not have an end tag. By contrast, XHTML requires all elements to have an opening tag or a closing tag. XHTML, however, also introduces a new shortcut: an XHTML tag may be opened and closed within the same tag, by including a slash before the end of the tag like this: <br/>. The introduction of this shorthand, which is not used in the SGML declaration for HTML 4. 01, may confuse earlier software unfamiliar with this new convention.

To understand the subtle differences between HTML and XHTML, consider the transformation of a valid and well-formed XHTML 1. 0 document that adheres to Appendix C (see below) into a valid HTML 4. 01 document. To make this translation requires the following steps:

1. The language for an element should be specified with a lang attribute rather than the XHTML xml:lang attribute. XHTML uses XML's built in language-defining functionality attribute.
2. Remove the XML namespace (xmlns=URI). HTML has no facilities for namespaces.
3. Change the document type declaration from XHTML 1. 0 to HTML 4. 01. (see DTD section for further explanation).
4. If present, remove the XML declaration. (Typically this is: <?xml version="1. 0" encoding="utf-8"?>).
5. Ensure that the document’s MIME type is set to text/html. For both HTML and XHTML, this comes from the HTTP Content-Type header sent by the server.
6. Change the XML empty-element syntax to an HTML style empty element (<br/> to <br>).

Those are the main changes necessary to translate a document from XHTML 1. 0 to HTML 4. 01. To translate from HTML to XHTML would also require the addition of any omitted opening or closing tags. Whether coding in HTML or XHTML it may just be best to always include the optional tags within an HTML document rather than remembering which tags can be omitted.

A well-formed XHTML document adheres to all the syntax requirements of XML. A valid document adheres to the content specification for XHTML, which describes the document structure.

The W3C recommends several conventions to ensure an easy migration between HTML and XHTML (see HTML Compatibility Guidelines). The following steps can be applied to XHTML 1. 0 documents only:

• Include both xml:lang and lang attributes on any elements assigning language.
• Use the empty-element syntax only for elements specified as empty in HTML.
• Include an extra space in empty-element tags: for example <br /> instead of <br/>.
• Include explicit close tags for elements that permit content but are left empty (for example, <div></div>, not <div />).
• Omit the XML declaration.

By carefully following the W3C’s compatibility guidelines, a user agent should be able to interpret the document equally as HTML or XHTML. For documents that are XHTML 1. 0 and have been made compatible in this way, the W3C permits them to be served either as HTML (with a text/html MIME type), or as XHTML (with an application/xhtml+xml or application/xml MIME type). An Internet media type, originally called a MIME type after MIME and sometimes a Content-type after the name of a header in several protocols whose value When delivered as XHTML, browsers should use an XML parser, which adheres strictly to the XML specifications for parsing the document's contents.

Transitional versus Strict

The latest SGML-based specification HTML 4. 01 and the earliest XHTML version include three sub-specifications: Strict, Transitional (once called Loose), and Frameset. The Strict variant represents the standard proper, whereas the Transitional and Frameset variants were developed to assist in the transition from earlier versions of HTML (including HTML 3. 2). The Transitional and Frameset variants allow for presentational markup whereas the Strict variant encourages the use of style sheets through its omission of most presentational markup.

The primary differences which make the Transitional variant more permissive than the Strict variant (the differences as the same in HTML 4 and XHTML 1. 0) are:

• A looser content model
  • Inline elements and plain text (#PCDATA) are allowed directly in: body, blockquote, form, noscript and noframes
• Presentation related elements
  • underline (u)
  • strike-through (s and strike)
  • center
  • font
  • basefont
• Presentation related attributes
  • background and bgcolor attributes for body element.
  • align attribute on div, form, paragraph (p), and heading (h1. . . h6) elements
  • align, noshade, size, and width attributes on hr element
  • align, border, vspace, and hspace attributes on img and object elements
  • align attribute on legend and caption elements
  • align and bgcolor on table element
  • nowrap, bgcolor, width, height on td and th elements
  • bgcolor attribute on tr element
  • clear attribute on br element
  • compact attribute on dl, dir and menu elements
  • type, compact, and start attributes on ol and ul elements
  • type and value attributes on li element
  • width attribute on pre element
• Additional elements in Transitional specification
  • menu list (no substitute, though unordered list is recommended; may return in XHTML 2. 0 specification)
  • dir list (no substitute, though unordered list is recommended)
  • isindex (element requires server-side support and is typically added to documents server-side)
  • applet (deprecated in favor of object element)
• The language attribute on script element (presumably redundant with type attribute, though this is maintained for legacy reasons).
• Frame related entities
  • frameset element (used in place of body for frameset DTD)
  • frame element
  • iframe
  • noframes
  • target attribute on anchor, client-side image-map (imagemap), link, form, and base elements

Frameset versus transitional

In addition to the above transitional differences, the frameset specifications (whether XHTML 1. 0 or HTML 4. 01) specifies a different content model:

<html>
 <head>
  <title></title>
  <!-- other head elements -->
 </head>
 
 <!-- frameset replaces body -->
 <frameset>
 
  <!-- frame definitions -->
  <frame></frame>
  <!-- , . . .  -->
 
  <!-- optional: alternate page body for frames-incompatible user agents -->
  <noframes>
   <body></body>
  </noframes>
 
 </frameset>
</html>

Summary of flavors

As this list demonstrates, the loose flavors of the specification are maintained for legacy support. However, contrary to popular misconceptions, the move to XHTML does not imply a removal of this legacy support. Rather the X in XML stands for extensible and the W3C is modularizing the entire specification and opening it up to independent extensions. The primary achievement in the move from XHTML 1. 0 to XHTML 1. 1 is the modularization of the entire specification. The strict version of HTML is deployed in XHTML 1. 1 through a set of modular extensions to the base XHTML 1. 1 specification. Likewise someone looking for the loose (transitional) or frameset specifications will find similar extended XHTML 1. 1 support (much of it is contained in the legacy or frame modules). The modularization also allows for separate features to develop on their own timetable. So for example XHTML 1. 1 will allow quicker migration to emerging XML standards such as MathML (a presentational and semantic math language based on XML) and XForms — a new highly advanced web-form technology to replace the existing HTML forms. Mathematical Markup Language ( MathML) is an application of XML for describing mathematical notations and capturing both its structure and content XForms is an XML format for the specification of a data processing model for XML data and User interface (s for the XML data such as web forms.

In summary, the HTML 4. 01 specification primarily reined in all the various HTML implementations into a single clear written specification based on SGML. XHTML 1. 0, ported this specification, as is, to the new XML defined specification. Next, XHTML 1. 1 takes advantage of the extensible nature of XML and modularizes the whole specification. XHTML 2. 0 will be the first step in adding new features to the specification in a standards-body-based approach.

Hypertext features not in HTML

HTML lacks some of the features found in earlier hypertext systems, such as typed links, transclusion, source tracking, fat links, and more. A typed link in a Hypertext system is a link to another document or part of a document that includes information about the character of the link In Computer science, transclusion is the inclusion of part of a document into another document by reference Source tracking pertains to the ability of some Hypertext systems to rigorously track the exact source of every document or partial document included in the system that A fat link is a Hyperlink which leads to multiple endpoints The hyperlinks that are attached to the same design object can be grouped into a fat link for representational ^[20] Even some hypertext features that were in early versions of HTML have been ignored by most popular web browsers until recently, such as the link element and in-browser Web page editing. In computing a hyperlink is a Reference or Navigation element in a Document to another Section of the same document or to another

Sometimes Web services or browser manufacturers remedy these shortcomings. For instance, wikis and content management systems allow surfers to edit the Web pages they visit. A wiki is a page or collection of Web pages designed to enable anyone who accesses it to contribute or modify content using a simplified Markup language. A content management system ( CMS) is a computer application used to create edit manage and publish content in a consistently organized fashion

See also

References

External links

• HTML 4.01, the last valid specification
• Dave Raggett's Introduction to HTML
• Empty elements in SGML, HTML, XML, and XHTML
• A list of all valid XHTML elements, usage and examples
• html codes Charts to make diacriticals, foreign language characters, and accent marks such as © ¿ á ü ç
• HTML editor Allows live preview of inserted HTML code
• Cheat Sheets of HTML/CSS

HTML Markup Validators

• W3C's Markup Validator
• WDG HTML Validator
• Off-line HTML Validator v1.0 for Windows
• Validator.nu

Tutorials

• HTML Dog
• HTML.net
• HTML Tree
• Pagetutor
• W3Schools

Standard HTML specifications

• Refer to the HTML version history section

Other specifications

• Web Applications 1.0 A specification generally referred to as "HTML 5". The Web Hypertext Application Technology working group are an independent initiative who cooperate with the W3C.