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Hypertext
Hypertext
Markup Language (HTML) is the standard markup language for creating web pages and web applications. With Cascading Style Sheets (CSS) and JavaScript, it forms a triad of cornerstone technologies for the World Wide Web.[4] Web browsers receive HTML
HTML
documents from a web server or from local storage and render the documents into multimedia web pages. HTML
HTML
describes the structure of a web page semantically and originally included cues for the appearance of the document. HTML
HTML
elements are the building blocks of HTML
HTML
pages. With HTML constructs, images and other objects such as interactive forms may be embedded into the rendered page. HTML
HTML
provides a means to create structured documents by denoting structural semantics for text such as headings, paragraphs, lists, links, quotes and other items. HTML elements are delineated by tags, written using angle brackets. Tags such as <img /> and <input /> directly introduce content into the page. Other tags such as <p>...</p> surround and provide information about document text and may include other tags as sub-elements. Browsers do not display the HTML
HTML
tags, but use them to interpret the content of the page. HTML
HTML
can embed programs written in a scripting language such as JavaScript
JavaScript
which affects the behavior and content of web pages. Inclusion of CSS
CSS
defines the look and layout of content. The World Wide Web Consortium (W3C), maintainer of both the HTML
HTML
and the CSS standards, has encouraged the use of CSS
CSS
over explicit presentational HTML
HTML
since 1997.[5]

Contents

1 History

1.1 Development 1.2 HTML
HTML
versions timeline

1.2.1 HTML
HTML
draft version timeline 1.2.2 XHTML
XHTML
versions

2 Markup

2.1 Elements

2.1.1 Element examples 2.1.2 Attributes

2.2 Character and entity references 2.3 Data types 2.4 Document type declaration

3 Semantic HTML 4 Delivery

4.1 HTTP 4.2 HTML
HTML
e-mail 4.3 Naming conventions 4.4 HTML
HTML
Application

5 HTML4 variations

5.1 SGML-based versus XML-based HTML 5.2 Transitional versus strict 5.3 Frameset versus transitional 5.4 Summary of specification versions

6 HTML5
HTML5
variants

6.1 WHATWG
WHATWG
HTML
HTML
versus HTML5

7 Hypertext
Hypertext
features not in HTML 8 WYSIWYG
WYSIWYG
editors 9 See also 10 References 11 External links

History

The historic logo made by the W3C

An example website written in HTML

Development

Tim Berners-Lee

In 1980, physicist Tim Berners-Lee, a contractor at CERN, proposed and prototyped ENQUIRE, a system for CERN
CERN
researchers to use and share documents. In 1989, Berners-Lee wrote a memo proposing an Internet-based hypertext system.[6] Berners-Lee specified HTML
HTML
and wrote the browser and server software in late 1990. That year, Berners-Lee and CERN
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[7] from 1990 he listed[8] "some of the many areas in which hypertext is used" and put an encyclopedia first. The first publicly available description of HTML
HTML
was a document called " HTML
HTML
Tags", first mentioned on the Internet
Internet
by Tim Berners-Lee
Tim Berners-Lee
in late 1991.[9][10] It describes 18 elements comprising the initial, relatively simple design of HTML. Except for the hyperlink tag, these were strongly influenced by SGMLguid, an in-house Standard Generalized Markup Language (SGML)-based documentation format at CERN. Eleven of these elements still exist in HTML
HTML
4.[11] HTML
HTML
is a markup language that web browsers use to interpret and compose text, images, and other material into visual or audible web pages. Default characteristics for every item of HTML
HTML
markup are defined in the browser, and these characteristics can be altered or enhanced by the web page designer's additional use of CSS. 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
SGML
concept of generalized markup is based on elements (nested annotated ranges with attributes) rather than merely print effects, with also the separation of structure and markup; HTML
HTML
has been progressively moved in this direction with CSS. Berners-Lee considered HTML
HTML
to be an application of SGML. It was formally defined as such by the Internet
Internet
Engineering Task Force (IETF) with the mid-1993 publication of the first proposal for an HTML specification, the " Hypertext
Hypertext
Markup Language (HTML)" Internet
Internet
Draft by Berners-Lee and Dan Connolly, which included an SGML
SGML
Document type definition to define the grammar.[12][13] 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.[14] 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.[15] After the HTML
HTML
and HTML+ drafts expired in early 1994, the IETF created an HTML
HTML
Working Group, which in 1995 completed " HTML
HTML
2.0", the first HTML
HTML
specification intended to be treated as a standard against which future implementations should be based.[16] Further development under the auspices of the IETF was stalled by competing interests. Since 1996, the HTML
HTML
specifications have been maintained, with input from commercial software vendors, by the World Wide Web Consortium (W3C).[17] However, in 2000, HTML
HTML
also became an international standard (ISO/IEC 15445:2000). HTML
HTML
4.01 was published in late 1999, with further errata published through 2001. In 2004, development began on HTML5
HTML5
in the Web Hypertext
Hypertext
Application Technology Working Group (WHATWG), which became a joint deliverable with the W3C in 2008, and completed and standardized on 28 October 2014.[18] HTML
HTML
versions timeline

November 24, 1995 HTML
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)

January 14, 1997 HTML
HTML
3.2[19] was published as a W3C
W3C
Recommendation. It was the first version developed and standardized exclusively by the W3C, as the IETF had closed its HTML Working Group on September 12, 1996.[20] Initially code-named "Wilbur",[21] HTML
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.[17] A markup for mathematical formulas similar to that in HTML
HTML
was not standardized until 14 months later in MathML. December 18, 1997 HTML
HTML
4.0[22] was published as a W3C
W3C
Recommendation. It offers three variations:

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",[21] HTML
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. HTML
HTML
4 is an SGML
SGML
application conforming to ISO 8879 – SGML.[23] April 24, 1998 HTML
HTML
4.0[24] was reissued with minor edits without incrementing the version number. December 24, 1999 HTML
HTML
4.01[25] was published as a W3C
W3C
Recommendation. It offers the same three variations as HTML
HTML
4.0 and its last errata were published on May 12, 2001. May 2000 ISO/IEC 15445:2000[26][27] ("ISO HTML", based on HTML
HTML
4.01 Strict) was published as an ISO/IEC international standard. In the ISO this standard falls in the domain of the ISO/IEC JTC1/SC34 (ISO/IEC Joint Technical Committee 1, Subcommittee 34 – Document description and processing languages).[26] After HTML
HTML
4.01, there was no new version of HTML
HTML
for many years as development of the parallel, XML-based language XHTML
XHTML
occupied the W3C's HTML Working Group through the early and mid-2000s. October 28, 2014 HTML5[28] was published as a W3C
W3C
Recommendation.[29] November 1, 2016 HTML
HTML
5.1[30] was published as a W3C
W3C
Recommendation.[31][32] December 14, 2017 HTML
HTML
5.2[33] was published as a W3C
W3C
Recommendation.[34][35]

HTML
HTML
draft version timeline

Logo of HTML5

October 1991 HTML
HTML
Tags,[9] an informal CERN
CERN
document listing 18 HTML
HTML
tags, was first mentioned in public. June 1992 First informal draft of the HTML
HTML
DTD,[36] with seven[37][38][39] subsequent revisions (July 15, August 6, August 18, November 17, November 19, November 20, November 22) November 1992 HTML
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[39] June 1993 Hypertext
Hypertext
Markup Language[40] was published by the IETF IIIR Working Group as an Internet
Internet
Draft (a rough proposal for a standard). It was replaced by a second version[41] one month later, followed by six further drafts published by IETF itself[42] that finally led to HTML 2.0 in RFC 1866. November 1993 HTML+ was published by the IETF as an Internet
Internet
Draft and was a competing proposal to the Hypertext
Hypertext
Markup Language draft. It expired in May 1994. April 1995 (authored March 1995) HTML
HTML
3.0[43] was proposed as a standard to the IETF, but the proposal expired five months later (28 September 1995)[44] 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.[44] W3C
W3C
began development of its own Arena browser as a test bed for HTML 3 and Cascading Style Sheets,[45][46][47] but HTML
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.[17] Browser vendors, including Microsoft
Microsoft
and Netscape
Netscape
at the time, chose to implement different subsets of HTML
HTML
3's draft features as well as to introduce their own extensions to it.[17] (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."[17] Dave Raggett, who has been a W3C
W3C
Fellow for many years, has commented for example: "To a certain extent, Microsoft
Microsoft
built its business on the Web by extending HTML
HTML
features."[17] January 2008 HTML5
HTML5
was published as a Working Draft by the W3C.[48] Although its syntax closely resembles that of SGML, HTML5
HTML5
has abandoned any attempt to be an SGML
SGML
application and has explicitly defined its own "html" serialization, in addition to an alternative XML-based X HTML5
HTML5
serialization.[49] 2011  HTML5
HTML5
– Last Call On 14 February 2011, the W3C
W3C
extended the charter of its HTML
HTML
Working Group with clear milestones for HTML5. In May 2011, the working group advanced HTML5
HTML5
to "Last Call", an invitation to communities inside and outside W3C
W3C
to confirm the technical soundness of the specification. The W3C
W3C
developed a comprehensive test suite to achieve broad interoperability for the full specification by 2014, which was the target date for recommendation.[50] In January 2011, the WHATWG renamed its "HTML5" living standard to "HTML". The W3C
W3C
nevertheless continues its project to release HTML5.[51] 2012  HTML5
HTML5
– Candidate Recommendation In July 2012, WHATWG
WHATWG
and W3C
W3C
decided on a degree of separation. W3C will continue the HTML5
HTML5
specification work, focusing on a single definitive standard, which is considered as a "snapshot" by WHATWG. The WHATWG
WHATWG
organization will continue its work with HTML5
HTML5
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.[52] In December 2012, W3C
W3C
designated HTML5
HTML5
as a Candidate Recommendation.[53] The criterion for advancement to W3C Recommendation is "two 100% complete and fully interoperable implementations".[54] 2014  HTML5
HTML5
– Proposed Recommendation and Recommendation In September 2014, W3C
W3C
moved HTML5
HTML5
to Proposed Recommendation.[55] On 28 October 2014, HTML5
HTML5
was released as a stable W3C Recommendation,[56] meaning the specification process is complete.[57]

XHTML
XHTML
versions Main article: XHTML XHTML
XHTML
is a separate language that began as a reformulation of HTML 4.01 using XML
XML
1.0. It is no longer being developed as a separate standard.

XHTML
XHTML
1.0 was published as a W3C Recommendation
W3C Recommendation
on January 26, 2000,[58] and was later revised and republished on August 1, 2002. It offers the same three variations as HTML
HTML
4.0 and 4.01, reformulated in XML, with minor restrictions. XHTML
XHTML
1.1[59] was published as a W3C Recommendation
W3C Recommendation
on May 31, 2001. It is based on XHTML
XHTML
1.0 Strict, but includes minor changes, can be customized, and is reformulated using modules in the W3C recommendation "Modularization of XHTML", which was published on April 10, 2001.[60] XHTML
XHTML
2.0 was a working draft, work on it was abandoned in 2009 in favor of work on HTML5
HTML5
and XHTML5.[61][62][63] XHTML
XHTML
2.0 was incompatible with XHTML
XHTML
1.x and, therefore, would be more accurately characterized as an XHTML-inspired new language than an update to XHTML
XHTML
1.x. An XHTML
XHTML
syntax, known as "XHTML5.1", is being defined alongside HTML5 in the HTML5
HTML5
draft.[64]

Markup HTML
HTML
markup consists of several key components, including those called tags (and their attributes), character-based data types, character references and entity references. HTML
HTML
tags most commonly come in pairs like <h1> and </h1>, although some represent empty elements and so are unpaired, for example <img>. The first tag in such a pair is the start tag, and the second is the end tag (they are also called opening tags and closing tags). Another important component is the HTML
HTML
document type declaration, which triggers standards mode rendering. The following is an example of the classic "Hello, World!" program, a common test employed for comparing programming languages, scripting languages and markup languages. This example is made using 9 source lines of code:

<!DOCTYPE html> <html> <head> <title>This is a title</title> </head> <body> <p>Hello world!</p> </body> </html>

(The text between <html> and </html> describes the web page, and the text between <body> and </body> is the visible page content. The markup text "<title>This is a title</title>" defines the browser page title.) The Document Type Declaration <!DOCTYPE html> is for HTML5. If a declaration is not included, various browsers will revert to "quirks mode" for rendering.[65] Elements Main article: HTML
HTML
element HTML
HTML
documents imply a structure of nested HTML
HTML
elements. These are indicated in the document by HTML
HTML
tags, enclosed in angle brackets thus: <p>[66] In the simple, general case, the extent of an element is indicated by a pair of tags: a "start tag" <p> and "end tag" </p>. The text content of the element, if any, is placed between these tags. Tags may also enclose further tag markup between the start and end, including a mixture of tags and text. This indicates further (nested) elements, as children of the parent element. The start tag may also include attributes within the tag. These indicate other information, such as identifiers for sections within the document, identifiers used to bind style information to the presentation of the document, and for some tags such as the <img> used to embed images, the reference to the image resource. Some elements, such as the line break <br>, do not permit any embedded content, either text or further tags. These require only a single empty tag (akin to a start tag) and do not use an end tag. Many tags, particularly the closing end tag for the very commonly used paragraph element <p>, are optional. An HTML
HTML
browser or other agent can infer the closure for the end of an element from the context and the structural rules defined by the HTML
HTML
standard. These rules are complex and not widely understood by most HTML
HTML
coders. The general form of an HTML element is therefore: <tag attribute1="value1" attribute2="value2">''content''</tag>. Some HTML
HTML
elements are defined as empty elements and take the form <tag attribute1="value1" attribute2="value2">. Empty elements may enclose no content, for instance, the <br> tag or the inline <img> tag. The name of an HTML element is the name used in the tags. Note that the end tag's name is preceded by a slash character, "/", and that in empty elements the end tag is neither required nor allowed. If attributes are not mentioned, default values are used in each case. Element examples Header of the HTML
HTML
document: <head>...</head>. The title is included in the head, for example:

<head> <title>The Title</title> </head>

Headings: HTML
HTML
headings are defined with the <h1> to <h6> tags:

<h1>Heading level 1</h1> <h2>Heading level 2</h2> <h3>Heading level 3</h3> <h4>Heading level 4</h4> <h5>Heading level 5</h5> <h6>Heading level 6</h6>

Paragraphs:

<p> Paragraph
Paragraph
1</p> <p> Paragraph
Paragraph
2</p>

Line breaks:<br>. The difference between <br> and <p> is that "br" breaks a line without altering the semantic structure of the page, whereas "p" sections the page into paragraphs. Note also that "br" is an empty element in that, although it may have attributes, it can take no content and it may not have an end tag.

<p>This <br> is a paragraph <br> with <br> line breaks</p>

This is a link in HTML. To create a link the <a> tag is used. The href= attribute holds the URL address of the link.

<a href="https://www.wikipedia.org/">A link to Wikipedia!</a>

Inputs: There are many possible ways a user can give input/s like:

1 <input type="text" /> <!-- This is for text input --> 2 <input type="file" /> <!-- This is for uploading files --> 3 <input type="checkbox" /> <!-- This is for checkboxes -->

Comments:

<!-- This is a comment -->

Comments can help in the understanding of the markup and do not display in the webpage. There are several types of markup elements used in HTML:

Structural markup indicates the purpose of text For example, <h2>Golf</h2> establishes "Golf" as a second-level heading. Structural markup does not denote any specific rendering, but most web browsers have default styles for element formatting. Content may be further styled using Cascading Style Sheets (CSS).[67] Presentational markup indicates the appearance of the text, regardless of its purpose For example, <b>boldface</b> indicates that visual output devices should render "boldface" in bold text, but gives little indication what devices that 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 other elements that may have equivalent visual renderings but that are more semantic in nature, such as <strong>strong text</strong> and <em>emphasised text</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
HTML
4.0 specification in favor of using CSS
CSS
for styling. Hypertext
Hypertext
markup makes parts of a document into links to other documents An anchor element creates a hyperlink in the document and its href attribute sets the link's target URL. For example, the HTML
HTML
markup, <a href="http://www.google.com/">Wikipedia</a>, will render the word as a hyperlink. To render an image as a hyperlink, an "img" element is inserted as content into the "a" element. Like "br", "img" is an empty element with attributes but no content or closing tag. <a href="http://example.org"><img src="image.gif" alt="descriptive text" width="50" height="50" border="0"></a>.

Attributes Main article: HTML
HTML
attribute 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
HTML
(but not XHTML) .[68][69] Leaving attribute values unquoted is considered unsafe.[70] 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,[9] like the ismap attribute for the img element.[71] There are several common attributes that may appear in many elements :

The id attribute provides a document-wide unique identifier for an element. This is used to identify the element so that stylesheets can alter its presentational properties, and scripts may alter, animate or delete its contents or presentation. Appended to the URL of the page, it provides a globally unique identifier for the element, typically a sub-section of the page. For example, the ID "Attributes" in https://en.wikipedia.org/wiki/HTML#Attributes The class attribute provides a way of classifying similar elements. This can be used for semantic or presentation purposes. For example, an HTML
HTML
document might semantically use the designation class="notation" to indicate that all elements with this class value are subordinate to the main text of the document. In presentation, 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. Class attributes are used semantically in microformats. Multiple class values may be specified; for example class="notation important" puts the element into both the "notation" and the "important" classes. An author may use the style attribute to assign presentational properties to a particular element. It is considered better practice to use an element's id or class attributes to select the element from within a stylesheet, though sometimes this can be too cumbersome for a simple, specific, or ad hoc styling. The title attribute is used to attach subtextual explanation to an element. In most browsers this attribute is displayed as a tooltip. The lang attribute identifies the natural language of the element's contents, which may be different from that of the rest of the document. For example, in an English-language document:

<p>Oh well, <span lang="fr">c'est la vie</span>, as they say in France.</p>

The abbreviation element, abbr, can be used to demonstrate some of these attributes :

<abbr id="anId" class="jargon" style="color:purple;" title=" Hypertext
Hypertext
Markup Language">HTML</abbr>

This example displays as HTML; in most browsers, pointing the cursor at the abbreviation should display the title text " Hypertext
Hypertext
Markup Language." Most elements take the language-related attribute dir to specify text direction, such as with "rtl" for right-to-left text in, for example, Arabic, Persian or Hebrew.[72] Character and entity references See also: List of XML
XML
and HTML
HTML
character entity references and Unicode and HTML As of version 4.0, HTML
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. 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 &lt; and &amp;, 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 &amp; or &#x26; or &#38; allows & to be included in the content of an element or in the value of an attribute. The double-quote character ("), when not used to quote an attribute value, must also be escaped as &quot; or &#x22; or &#34; when it appears within the attribute value itself. Equivalently, the single-quote character ('), when not used to quote an attribute value, must also be escaped as &#x27; or &#39; (or as &apos; in HTML5
HTML5
or XHTML
XHTML
documents[73][74]) when it appears within the attribute value itself. If document authors overlook the need to escape such characters, some browsers can be very forgiving and try to use context to guess their intent. The result is still invalid markup, which makes the document less accessible to other browsers and to other user agents that may try to parse the document for search and indexing purposes for example. Escaping also allows for characters that are not easily typed, or that are not available in the document's character encoding, to be represented within element and attribute content. For example, the acute-accented e (é), a character typically found only on Western European and South American keyboards, can be written in any HTML document as the entity reference &eacute; or as the numeric references &#xE9; or &#233;, using characters that are available on all keyboards and are supported in all character encodings. Unicode
Unicode
character encodings such as UTF-8
UTF-8
are compatible with all modern browsers and allow direct access to almost all the characters of the world's writing systems.[75] Data types HTML
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. All of these data types are specializations of character data. Document type declaration HTML
HTML
documents are required to start with a Document Type Declaration (informally, a "doctype"). In browsers, the doctype helps to define the rendering mode—particularly whether to use quirks mode. The original purpose of the doctype was to enable parsing and validation of HTML
HTML
documents by SGML
SGML
tools based on the Document Type Definition (DTD). The DTD to which the DOCTYPE refers contains a machine-readable grammar specifying the permitted and prohibited content for a document conforming to such a DTD. Browsers, on the other hand, do not implement HTML
HTML
as an application of SGML
SGML
and by consequence do not read the DTD. HTML5
HTML5
does not define a DTD; therefore, in HTML5
HTML5
the doctype declaration is simpler and shorter:[76]

<!DOCTYPE html>

An example of an HTML
HTML
4 doctype

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

This declaration references the DTD for the "strict" version of HTML 4.01. SGML-based validators read the DTD in order to properly parse the document and to perform validation. In modern browsers, a valid doctype activates standards mode as opposed to quirks mode. In addition, HTML
HTML
4.01 provides Transitional and Frameset DTDs, as explained below. Transitional type is the most inclusive, incorporating current tags as well as older or "deprecated" tags, with the Strict DTD excluding deprecated tags. Frameset has all tags necessary to make frames on a page along with the tags included in transitional type[citation needed]. Semantic HTML Main article: Semantic HTML Semantic HTML is a way of writing HTML
HTML
that emphasizes the meaning of the encoded information over its presentation (look). HTML
HTML
has included semantic markup from its inception,[77] but has also included presentational markup, such as <font>, <i> and <center> tags. There are also the semantically neutral span and div tags. Since the late 1990s when Cascading Style Sheets
Cascading Style Sheets
were beginning to work in most browsers, web authors have been encouraged to avoid the use of presentational HTML
HTML
markup with a view to the separation of presentation and content.[78] In a 2001 discussion of the Semantic Web, Tim Berners-Lee
Tim Berners-Lee
and others gave examples of ways in which intelligent software "agents" may one day automatically crawl the web and find, filter and correlate previously unrelated, published facts for the benefit of human users.[79] Such agents are not commonplace even now, but some of the ideas of Web 2.0, mashups and price comparison websites may be coming close. The main difference between these web application hybrids and Berners-Lee's semantic agents lies in the fact that the current aggregation and hybridization of information is usually designed in by web developers, who already know the web locations and the API semantics of the specific data they wish to mash, compare and combine. An important type of web agent that does crawl and read web pages automatically, without prior knowledge of what it might find, is the web crawler or search-engine spider. These software agents are dependent on the semantic clarity of web pages they find as they use various techniques and algorithms to read and index millions of web pages a day and provide web users with search facilities without which the World Wide Web's usefulness would be greatly reduced. In order for search-engine spiders to be able to rate the significance of pieces of text they find in HTML
HTML
documents, and also for those creating mashups and other hybrids as well as for more automated agents as they are developed, the semantic structures that exist in HTML
HTML
need to be widely and uniformly applied to bring out the meaning of published text.[80] Presentational markup tags are deprecated in current HTML
HTML
and XHTML recommendations and are illegal in HTML5[citation needed]. Good semantic HTML
HTML
also improves the accessibility of web documents (see also Web Content Accessibility
Accessibility
Guidelines). For example, when a screen reader or audio browser can correctly ascertain the structure of a document, it will not waste the visually impaired user's time by reading out repeated or irrelevant information when it has been marked up correctly. Delivery HTML
HTML
documents can be delivered by the same means as any other computer file. However, they are most often delivered either by HTTP from a web server or by email. HTTP Main article: Hypertext
Hypertext
Transfer Protocol The World Wide Web
World Wide Web
is composed primarily of HTML
HTML
documents transmitted from web servers to web browsers using the Hypertext
Hypertext
Transfer Protocol (HTTP). However, HTTP is used to serve images, sound, and other content, in addition to HTML. To allow the web browser to know how to handle each document it receives, other information is transmitted along with the document. This meta data usually includes the MIME type (e.g. text/html or application/xhtml+xml) and the character encoding (see Character encoding
Character encoding
in HTML). In modern browsers, the MIME type that is sent with the HTML
HTML
document may affect how the document is initially interpreted. A document sent with the XHTML
XHTML
MIME type is expected to be well-formed XML; syntax errors may cause the browser to fail to render it. The same document sent with the HTML
HTML
MIME type might be displayed successfully, since some browsers are more lenient with HTML. The W3C
W3C
recommendations state that XHTML
XHTML
1.0 documents that follow guidelines set forth in the recommendation's Appendix C may be labeled with either MIME Type.[81] XHTML
XHTML
1.1 also states that XHTML
XHTML
1.1 documents should[82] be labeled with either MIME type.[83] HTML
HTML
e-mail Main article: HTML
HTML
email Most graphical email clients allow the use of a subset of HTML
HTML
(often ill-defined) to provide formatting and semantic markup not available with plain text. This may include typographic information like coloured headings, emphasized and quoted text, inline images and diagrams. Many such clients include both a GUI editor for composing HTML
HTML
e-mail messages and a rendering engine for displaying them. Use of HTML
HTML
in e-mail is criticized by some because of compatibility issues, because it can help disguise phishing attacks, because of accessibility issues for blind or visually impaired people, because it can confuse spam filters and because the message size is larger than plain text. Naming conventions The most common filename extension for files containing HTML
HTML
is .html. A common abbreviation of this is .htm, which originated because some early operating systems and file systems, such as DOS
DOS
and the limitations imposed by FAT data structure, limited file extensions to three letters.[84] HTML
HTML
Application Main article: HTML
HTML
Application An HTML Application (HTA; file extension ".hta") is a Microsoft Windows application that uses HTML
HTML
and Dynamic HTML in a browser to provide the application's graphical interface. A regular HTML
HTML
file is confined to the security model of the web browser's security, communicating only to web servers and manipulating only webpage objects and site cookies. An HTA runs as a fully trusted application and therefore has more privileges, like creation/editing/removal of files and Windows Registry
Windows Registry
entries. Because they operate outside the browser's security model, HTAs cannot be executed via HTTP, but must be downloaded (just like an EXE file) and executed from local file system. HTML4 variations Since its inception, HTML
HTML
and its associated protocols gained acceptance relatively quickly.[by whom?] However, no clear standards existed in the early years of the language. Though its creators originally conceived of HTML
HTML
as a semantic language devoid of presentation details,[85] practical uses pushed many presentational elements and attributes into the language, driven largely by the various browser vendors. The latest standards surrounding HTML
HTML
reflect efforts to overcome the sometimes chaotic development of the language[86] and to create a rational foundation for building both meaningful and well-presented documents. To return HTML
HTML
to its role as a semantic language, the W3C
W3C
has developed style languages such as CSS and XSL to shoulder the burden of presentation. In conjunction, the HTML
HTML
specification has slowly reined in the presentational elements. There are two axes differentiating various variations of HTML
HTML
as currently specified: SGML-based HTML
HTML
versus XML-based HTML
HTML
(referred to as XHTML) on one axis, and strict versus transitional (loose) versus frameset on the other axis. SGML-based versus XML-based HTML One difference in the latest HTML
HTML
specifications lies in the distinction between the SGML-based specification and the XML-based specification. The XML-based specification is usually called XHTML
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
W3C
intended XHTML
XHTML
1.0 to be identical to HTML
HTML
4.01 except where limitations of XML
XML
over the more complex SGML require workarounds. Because XHTML
XHTML
and HTML
HTML
are closely related, they are sometimes documented in parallel. In such circumstances, some authors conflate the two names as (X)HTML
(X)HTML
or X(HTML). Like HTML
HTML
4.01, XHTML
XHTML
1.0 has three sub-specifications: strict, transitional and frameset. Aside from the different opening declarations for a document, the differences between an HTML
HTML
4.01 and XHTML
XHTML
1.0 document—in each of the corresponding DTDs—are largely syntactic. The underlying syntax of HTML
HTML
allows many shortcuts that XHTML
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
XHTML
requires all elements to have an opening tag and a closing tag. XHTML, however, also introduces a new shortcut: an XHTML
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
SGML
declaration for HTML
HTML
4.01, may confuse earlier software unfamiliar with this new convention. A fix for this is to include a space before closing the tag, as such: <br />.[87] To understand the subtle differences between HTML
HTML
and XHTML, consider the transformation of a valid and well-formed XHTML
XHTML
1.0 document that adheres to Appendix C (see below) into a valid HTML
HTML
4.01 document. To make this translation requires the following steps:

The language for an element should be specified with a lang attribute rather than the XHTML
XHTML
xml:lang attribute. XHTML
XHTML
uses XML's built in language-defining functionality attribute. Remove the XML
XML
namespace (xmlns=URI). HTML
HTML
has no facilities for namespaces. Change the document type declaration from XHTML
XHTML
1.0 to HTML
HTML
4.01. (see DTD section for further explanation). If present, remove the XML
XML
declaration. (Typically this is: <?xml version="1.0" encoding="utf-8"?>). Ensure that the document's MIME type is set to text/html. For both HTML
HTML
and XHTML, this comes from the HTTP Content-Type header sent by the server. Change the XML
XML
empty-element syntax to an HTML
HTML
style empty element (<br /> to <br>).

Those are the main changes necessary to translate a document from XHTML
XHTML
1.0 to HTML
HTML
4.01. To translate from HTML
HTML
to XHTML
XHTML
would also require the addition of any omitted opening or closing tags. Whether coding in HTML
HTML
or XHTML
XHTML
it may just be best to always include the optional tags within an HTML
HTML
document rather than remembering which tags can be omitted. A well-formed XHTML
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
W3C
recommends several conventions to ensure an easy migration between HTML
HTML
and XHTML
XHTML
(see HTML
HTML
Compatibility Guidelines). The following steps can be applied to XHTML
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
XML
declaration.

By carefully following the W3C's compatibility guidelines, a user agent should be able to interpret the document equally as HTML
HTML
or XHTML. For documents that are XHTML
XHTML
1.0 and have been made compatible in this way, the W3C
W3C
permits them to be served either as HTML
HTML
(with a text/html MIME type), or as XHTML
XHTML
(with an application/xhtml+xml or application/xml MIME type). When delivered as XHTML, browsers should use an XML
XML
parser, which adheres strictly to the XML
XML
specifications for parsing the document's contents. Transitional versus strict HTML
HTML
4 defined three different versions of the language: Strict, Transitional (once called Loose) and Frameset. The Strict version is intended for new documents and is considered best practice, while the Transitional and Frameset versions were developed to make it easier to transition documents that conformed to older HTML
HTML
specification or didn't conform to any specification to a version of HTML
HTML
4. The Transitional and Frameset versions allow for presentational markup, which is omitted in the Strict version. Instead, cascading style sheets are encouraged to improve the presentation of HTML
HTML
documents. Because XHTML
XHTML
1 only defines an XML
XML
syntax for the language defined by HTML
HTML
4, the same differences apply to XHTML
XHTML
1 as well. The Transitional version allows the following parts of the vocabulary, which are not included in the Strict version:

A looser content model

Inline elements and plain text are allowed directly in: body, blockquote, form, noscript and noframes

Presentation related elements

underline (u)(Deprecated. can confuse a visitor with a hyperlink.) strike-through (s) center (Deprecated. use CSS
CSS
instead.) font (Deprecated. use CSS
CSS
instead.) basefont (Deprecated. use CSS
CSS
instead.)

Presentation related attributes

background (Deprecated. use CSS
CSS
instead.) and bgcolor (Deprecated. use CSS
CSS
instead.) attributes for body (required element according to the W3C.) element. align (Deprecated. use CSS
CSS
instead.) attribute on div, form, paragraph (p) and heading (h1...h6) elements align (Deprecated. use CSS
CSS
instead.), noshade (Deprecated. use CSS instead.), size (Deprecated. use CSS
CSS
instead.) and width (Deprecated. use CSS
CSS
instead.) attributes on hr element align (Deprecated. use CSS
CSS
instead.), border, vspace and hspace attributes on img and object (caution: the object element is only supported in Internet
Internet
Explorer (from the major browsers)) elements align (Deprecated. use CSS
CSS
instead.) attribute on legend and caption elements align (Deprecated. use CSS
CSS
instead.) and bgcolor (Deprecated. use CSS instead.) on table element nowrap (Obsolete), bgcolor (Deprecated. use CSS
CSS
instead.), width, height on td and th elements bgcolor (Deprecated. use CSS
CSS
instead.) attribute on tr element clear (Obsolete) attribute on br element compact attribute on dl, dir and menu elements type (Deprecated. use CSS
CSS
instead.), compact (Deprecated. use CSS instead.) and start (Deprecated. use CSS
CSS
instead.) attributes on ol and ul elements type and value attributes on li element width attribute on pre element

Additional elements in Transitional specification

menu (Deprecated. use CSS
CSS
instead.) list (no substitute, though unordered list is recommended) dir (Deprecated. use CSS
CSS
instead.) list (no substitute, though unordered list is recommended) isindex (Deprecated.) (element requires server-side support and is typically added to documents server-side, form and input elements can be used as a substitute) applet (Deprecated. use the object element instead.)

The language (Obsolete) attribute on script element (redundant with the type attribute). Frame related entities

iframe noframes target (Deprecated in the map, link and form elements.) attribute on a, client-side image-map (map), link, form and base elements

The Frameset version includes everything in the Transitional version, as well as the frameset element (used instead of body) and the frame element. Frameset versus transitional In addition to the above transitional differences, the frameset specifications (whether XHTML
XHTML
1.0 or HTML
HTML
4.01) specify a different content model, with frameset replacing body, that contains either frame elements, or optionally noframes with a body. Summary of specification versions As this list demonstrates, the loose versions of the specification are maintained for legacy support. However, contrary to popular misconceptions, the move to XHTML
XHTML
does not imply a removal of this legacy support. Rather the X in XML
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
XHTML
1.1 is the modularization of the entire specification. The strict version of HTML
HTML
is deployed in XHTML
XHTML
1.1 through a set of modular extensions to the base XHTML
XHTML
1.1 specification. Likewise, someone looking for the loose (transitional) or frameset specifications will find similar extended XHTML
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
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
HTML
forms. In summary, the HTML
HTML
4 specification primarily reined in all the various HTML
HTML
implementations into a single clearly written specification based on SGML. XHTML
XHTML
1.0, ported this specification, as is, to the new XML
XML
defined specification. Next, XHTML
XHTML
1.1 takes advantage of the extensible nature of XML
XML
and modularizes the whole specification. XHTML
XHTML
2.0 was intended to be the first step in adding new features to the specification in a standards-body-based approach. HTML5
HTML5
variants WHATWG
WHATWG
HTML
HTML
versus HTML5 Main article: HTML5 The WHATWG
WHATWG
considers their work as living standard HTML
HTML
for what constitutes the state of the art in major browser implementations by Apple (Safari), Microsoft
Microsoft
(Edge), Google
Google
(Chrome), Mozilla (Firefox), Opera (Opera), and others. HTML5
HTML5
is specified by the HTML
HTML
Working Group of the W3C
W3C
following the W3C
W3C
process. As of 2013[update] both specifications are similar and mostly derived from each other, i.e., the work on HTML5
HTML5
started with an older WHATWG
WHATWG
draft, and later the WHATWG
WHATWG
living standard was based on HTML5
HTML5
drafts in 2011.[88][89] Hypertext
Hypertext
features not in HTML HTML
HTML
lacks some of the features found in earlier hypertext systems, such as source tracking, fat links and others.[90] Even some hypertext features that were in early versions of HTML
HTML
have been ignored by most popular web browsers until recently[when?], such as the link element and in-browser Web page
Web page
editing. Sometimes web developers or browser manufacturers remedy these shortcomings. For instance, wikis and content management systems allow surfers to edit the Web pages they visit. WYSIWYG
WYSIWYG
editors There are some WYSIWYG
WYSIWYG
editors (What You See Is What You Get), in which the user lays out everything as it is to appear in the HTML document using a graphical user interface (GUI), often similar to word processors. The editor renders the document rather than show the code, so authors do not require extensive knowledge of HTML. The WYSIWYG
WYSIWYG
editing model has been criticized,[91][92] primarily because of the low quality of the generated code; there are voices advocating a change to the WYSIWYM
WYSIWYM
model (What You See Is What You Mean). WYSIWYG
WYSIWYG
editors remain a controversial topic because of their perceived flaws such as:

Relying mainly on layout as opposed to meaning, often using markup that does not convey the intended meaning but simply copies the layout.[93] Often producing extremely verbose and redundant code that fails to make use of the cascading nature of HTML
HTML
and CSS. Often producing ungrammatical markup, called tag soup or semantically incorrect markup (such as <em> for italics). As a great deal of the information in HTML
HTML
documents is not in the layout, the model has been criticized for its "what you see is all you get"-nature.[94]

See also

Breadcrumb (navigation) Comparison of HTML
HTML
parsers Dynamic web page HTML
HTML
decimal character rendering List of document markup languages List of XML
XML
and HTML
HTML
character entity references Microdata (HTML) Microformat Polyglot markup Semantic HTML W3C
W3C
(X)HTML
(X)HTML
Validator

References

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Blog. 2012-12-17. Retrieved 2013-01-14.  ^ Jakob Nielsen (January 3, 2005). "Reviving Advanced Hypertext". Retrieved June 16, 2007.  ^ Sauer, C.: WYSIWIKI – Questioning WYSIWYG
WYSIWYG
in the Internet Age. In: Wikimania (2006) ^ Spiesser, J., Kitchen, L.: Optimization of HTML
HTML
automatically generated by WYSIWYG
WYSIWYG
programs. In: 13th International Conference on World Wide Web, pp. 355—364. WWW '04. ACM, New York, NY (New York, NY, U.S., May 17–20, 2004) ^ XHTML
XHTML
Reference: blockquote. Xhtml.com. Retrieved on 2012-02-16. ^ Doug Engelbart's INVISIBLE REVOLUTION . Invisiblerevolution.net. Retrieved on 2012-02-16.

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128 216 217 226 228 233 259 269 302 306 428 518 519 639

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3297 3307 3602 3864 3901 3977 4031 4157 4217 4909 5218 5428 5775 5776 5800 5964 6166 6344 6346 6385 6425 6429 6438 6523 6709 7001 7002 7098 7185 7200 7498 7736 7810 7811 7812 7813 7816 8000 8178 8217 8571 8583 8601 8632 8652 8691 8807 8820-5 8859

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10000–19999

10005 10006 10007 10116 10118-3 10160 10161 10165 10179 10206 10218 10303

-11 -21 -22 -28 -238

10383 10487 10585 10589 10646 10664 10746 10861 10957 10962 10967 11073 11170 11179 11404 11544 11783 11784 11785 11801 11898 11940 (-2) 11941 11941 (TR) 11992 12006 12182 12207 12234-2 13211

-1 -2

13216 13250 13399 13406-2 13450 13485 13490 13567 13568 13584 13616 14000 14031 14224 14289 14396 14443 14496

-2 -3 -6 -10 -11 -12 -14 -17 -20

14644 14649 14651 14698 14750 14764 14882 14971 15022 15189 15288 15291 15292 15398 15408 15444

-3

15445 15438 15504 15511 15686 15693 15706

-2

15707 15897 15919 15924 15926 15926 WIP 15930 16023 16262 16612-2 16750 16949 (TS) 17024 17025 17100 17203 17369 17442 17799 18000 18004 18014 18245 18629 18916 19005 19011 19092 (-1 -2) 19114 19115 19125 19136 19439 19500 19501 19502 19503 19505 19506 19507 19508 19509 19510 19600 19752 19757 19770 19775-1 19794-5 19831

20000+

20000 20022 20121 20400 21000 21047 21500 21827:2002 22000 23270 23271 23360 24517 24613 24617 24707 25178 25964 26000 26300 26324 27000 series 27000 27001 27002 27006 27729 28000 29110 29148 29199-2 29500 30170 31000 32000 38500 40500 42010 55000 80000

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List of International Electrotechnical Commission
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IEC standards

IEC 60027 IEC 60034 IEC 60038 IEC 60062 IEC 60063 IEC 60068 IEC 60112 IEC 60228 IEC 60269 IEC 60297 IEC 60309 IEC 60320 IEC 60364 IEC 60446 IEC 60559 IEC 60601 IEC 60870

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IEC 60906-1 IEC 60908 IEC 60929 IEC 60958

AES3 S/PDIF

IEC 61030 IEC 61131

IEC 61131-3

IEC 61158 IEC 61162 IEC 61334 IEC 61346 IEC 61355 IEC 61400 IEC 61499 IEC 61508 IEC 61511 IEC 61850 IEC 61851 IEC 61883 IEC 61960 IEC 61968 IEC 61970 IEC 62014-4 IEC 62056 IEC 62061 IEC 62196 IEC 62262 IEC 62264 IEC 62304 IEC 62325 IEC 62351 IEC 62365 IEC 62366 IEC 62379 IEC 62386 IEC 62455 IEC 62680 IEC 62682 IEC 62700

ISO/IEC standards

ISO/IEC 646 ISO/IEC 2022 ISO/IEC 4909 ISO/IEC 5218 ISO/IEC 6429 ISO/IEC 6523 ISO/IEC 7810 ISO/IEC 7811 ISO/IEC 7812 ISO/IEC 7813 ISO/IEC 7816 ISO/IEC 7942 ISO/IEC 8613 ISO/IEC 8632 ISO/IEC 8652 ISO/IEC 8859 ISO/IEC 9126 ISO/IEC 9293 ISO/IEC 9592 ISO/IEC 9593 ISO/IEC 9899 ISO/IEC 9945 ISO/IEC 9995 ISO/IEC 10021 ISO/IEC 10116 ISO/IEC 10165 ISO/IEC 10179 ISO/IEC 10646 ISO/IEC 10967 ISO/IEC 11172 ISO/IEC 11179 ISO/IEC 11404 ISO/IEC 11544 ISO/IEC 11801 ISO/IEC 12207 ISO/IEC 13250 ISO/IEC 13346 ISO/IEC 13522-5 ISO/IEC 13568 ISO/IEC 13818 ISO/IEC 14443 ISO/IEC 14496 ISO/IEC 14882 ISO/IEC 15288 ISO/IEC 15291 ISO/IEC 15408 ISO/IEC 15444 ISO/IEC 15445 ISO/IEC 15504 ISO/IEC 15511 ISO/IEC 15693 ISO/IEC 15897 ISO/IEC 15938 ISO/IEC 16262 ISO/IEC 17024 ISO/IEC 17025 ISO/IEC 18000 ISO/IEC 18004 ISO/IEC 18014 ISO/IEC 19752 ISO/IEC 19757 ISO/IEC 19770 ISO/IEC 19788 ISO/IEC 20000 ISO/IEC 21000 ISO/IEC 21827 ISO/IEC 23000 ISO/IEC 23003 ISO/IEC 23008 ISO/IEC 23270 ISO/IEC 23360 ISO/IEC 24707 ISO/IEC 24727 ISO/IEC 24744 ISO/IEC 24752 ISO/IEC 26300 ISO/IEC 27000 ISO/IEC 27000-series ISO/IEC 27002 ISO/IEC 27040 ISO/IEC 29119 ISO/IEC 33001 ISO/IEC 38500 ISO/IEC 42010 ISO/IEC 80000

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