HTML

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".htm" and ".html" redirect here. HTML_sentence_0

For other uses, see HTM. HTML_sentence_1

HTML_table_infobox_0

HTML (Hypertext Markup Language)HTML_table_caption_0
HTML_header_cell_0_0_0 HTML_cell_0_0_1
Internet media typeHTML_header_cell_0_1_0 text/htmlHTML_cell_0_1_1
Type codeHTML_header_cell_0_2_0 TEXTHTML_cell_0_2_1
Developed byHTML_header_cell_0_3_0 WHATWGHTML_cell_0_3_1
Initial releaseHTML_header_cell_0_4_0 1993; 27 years ago (1993)HTML_cell_0_4_1
Latest releaseHTML_header_cell_0_5_0 (2020)HTML_cell_0_5_1
Type of formatHTML_header_cell_0_6_0 HTML_cell_0_6_1
Container forHTML_header_cell_0_7_0 HTML elementsHTML_cell_0_7_1
Contained byHTML_header_cell_0_8_0 Web browserHTML_cell_0_8_1
Extended fromHTML_header_cell_0_9_0 SGMLHTML_cell_0_9_1
Extended toHTML_header_cell_0_10_0 XHTMLHTML_cell_0_10_1
Open format?HTML_header_cell_0_11_0 YesHTML_cell_0_11_1
WebsiteHTML_header_cell_0_12_0 HTML_cell_0_12_1

Hypertext Markup Language (HTML) is the standard markup language for documents designed to be displayed in a web browser. HTML_sentence_2

It can be assisted by technologies such as Cascading Style Sheets (CSS) and scripting languages such as JavaScript. HTML_sentence_3

Web browsers receive HTML documents from a web server or from local storage and render the documents into multimedia web pages. HTML_sentence_4

HTML describes the structure of a web page semantically and originally included cues for the appearance of the document. HTML_sentence_5

HTML elements are the building blocks of HTML pages. HTML_sentence_6

With HTML constructs, images and other objects such as interactive forms may be embedded into the rendered page. HTML_sentence_7

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_sentence_8

HTML elements are delineated by tags, written using angle brackets. HTML_sentence_9

Tags such as <img /> and <input /> directly introduce content into the page. HTML_sentence_10

Other tags such as

surround and provide information about document text and may include other tags as sub-elements. HTML_sentence_11 Browsers do not display the HTML tags, but use them to interpret the content of the page. HTML_sentence_12 HTML can embed programs written in a scripting language such as JavaScript, which affects the behavior and content of web pages. HTML_sentence_13 Inclusion of CSS defines the look and layout of content. HTML_sentence_14 The World Wide Web Consortium (W3C), former maintainer of the HTML and current maintainer of the CSS standards, has encouraged the use of CSS over explicit presentational HTML since 1997. HTML_sentence_15

History HTML_section_0

Development HTML_section_1

In 1980, physicist Tim Berners-Lee, a contractor at CERN, proposed and prototyped ENQUIRE, a system for CERN researchers to use and share documents. HTML_sentence_16

In 1989, Berners-Lee wrote a memo proposing an Internet-based hypertext system. HTML_sentence_17

Berners-Lee specified HTML and wrote the browser and server software in late 1990. HTML_sentence_18

That year, Berners-Lee and CERN data systems engineer Robert Cailliau collaborated on a joint request for funding, but the project was not formally adopted by CERN. HTML_sentence_19

In his personal notes from 1990 he listed "some of the many areas in which hypertext is used" and put an encyclopedia first. HTML_sentence_20

The first publicly available description of HTML was a document called , first mentioned on the Internet by Tim Berners-Lee in late 1991. HTML_sentence_21

It describes 18 elements comprising the initial, relatively simple design of HTML. HTML_sentence_22

Except for the hyperlink tag, these were strongly influenced by SGMLguid, an in-house Standard Generalized Markup Language (SGML)-based documentation format at CERN. HTML_sentence_23

Eleven of these elements still exist in HTML 4. HTML_sentence_24

HTML is a markup language that web browsers use to interpret and compose text, images, and other material into visual or audible web pages. HTML_sentence_25

Default characteristics for every item of 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. HTML_sentence_26

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. HTML_sentence_27

However, the 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 has been progressively moved in this direction with CSS. HTML_sentence_28

Berners-Lee considered HTML to be an application of SGML. HTML_sentence_29

It was formally defined as such by the Internet Engineering Task Force (IETF) with the mid-1993 publication of the first proposal for an HTML specification, the "Hypertext Markup Language (HTML)" Internet Draft by Berners-Lee and Dan Connolly, which included an SGML Document type definition to define the grammar. HTML_sentence_30

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. HTML_sentence_31

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. HTML_sentence_32

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. HTML_sentence_33

Further development under the auspices of the IETF was stalled by competing interests. HTML_sentence_34

Since 1996, the HTML specifications have been maintained, with input from commercial software vendors, by the World Wide Web Consortium (W3C). HTML_sentence_35

However, in 2000, HTML also became an international standard (ISO/IEC 15445:2000). HTML_sentence_36

HTML 4.01 was published in late 1999, with further errata published through 2001. HTML_sentence_37

In 2004, development began on HTML5 in the Web Hypertext Application Technology Working Group (WHATWG), which became a joint deliverable with the W3C in 2008, and completed and standardized on 28 October 2014. HTML_sentence_38

HTML versions timeline HTML_section_2

HTML 2 HTML_section_3

HTML_description_list_0

  • HTML_item_0_0
    • November 24, 1995: HTML 2.0 was published as RFC . Supplemental RFCs added capabilities:HTML_item_0_1
      • November 25, 1995: RFC  (form-based file upload)HTML_item_0_2
      • May 1996: RFC  (tables)HTML_item_0_3
      • August 1996: RFC  (client-side image maps)HTML_item_0_4
      • January 1997: RFC  (internationalization)HTML_item_0_5

HTML 3 HTML_section_4

HTML_description_list_1

  • HTML_item_1_6
    • January 14, 1997: HTML 3.2 was published as a W3C Recommendation. It was the first version developed and standardized exclusively by the W3C, as the IETF had closed its HTML Working Group on September 12, 1996.HTML_item_1_7
    • Initially code-named "Wilbur", HTML 3.2 dropped math formulas entirely, reconciled overlap among various proprietary extensions and adopted most of Netscape's visual markup tags. Netscape's blink element and Microsoft's marquee element were omitted due to a mutual agreement between the two companies. A markup for mathematical formulas similar to that in HTML was not standardized until 14 months later in MathML.HTML_item_1_8

HTML 4 HTML_section_5

HTML_description_list_2

  • HTML_item_2_9
    • December 18, 1997: HTML 4.0 was published as a W3C Recommendation. It offers three variations:HTML_item_2_10
      • Strict, in which deprecated elements are forbiddenHTML_item_2_11
      • Transitional, in which deprecated elements are allowedHTML_item_2_12
      • Frameset, in which mostly only frame related elements are allowed.HTML_item_2_13
    • Initially code-named "Cougar", HTML 4.0 adopted many browser-specific element types and attributes, but at the same time sought to phase out Netscape's visual markup features by marking them as deprecated in favor of style sheets. HTML 4 is an SGML application conforming to ISO 8879 – SGML.HTML_item_2_14
    • April 24, 1998: HTML 4.0 was reissued with minor edits without incrementing the version number.HTML_item_2_15
    • December 24, 1999: HTML 4.01 was published as a W3C Recommendation. It offers the same three variations as HTML 4.0 and its last were published on May 12, 2001.HTML_item_2_16
    • May 2000: ISO/IEC 15445:2000 ("ISO HTML", based on 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).HTML_item_2_17
    • After HTML 4.01, there was no new version of HTML for many years as development of the parallel, XML-based language XHTML occupied the W3C's HTML Working Group through the early and mid-2000s.HTML_item_2_18

HTML 5 HTML_section_6

Main article: HTML5 HTML_sentence_39

HTML_description_list_3

  • HTML_item_3_19
    • October 28, 2014: HTML5 was published as a W3C Recommendation.HTML_item_3_20
    • November 1, 2016: HTML 5.1 was published as a W3C Recommendation.HTML_item_3_21
    • December 14, 2017: HTML 5.2 was published as a W3C Recommendation.HTML_item_3_22

HTML draft version timeline HTML_section_7

HTML_description_list_4

  • October 1991: HTML Tags, an informal CERN document listing 18 HTML tags, was first mentioned in public.HTML_item_4_23
  • June 1992: First informal draft of the HTML DTD, with seven subsequent revisions (July 15, August 6, August 18, November 17, November 19, November 20, November 22)HTML_item_4_24
  • November 1992: HTML DTD 1.1 (the first with a version number, based on RCS revisions, which start with 1.1 rather than 1.0), an informal draftHTML_item_4_25
  • June 1993: Hypertext Markup Language was published by the IETF IIIR Working Group as an Internet Draft (a rough proposal for a standard). It was replaced by a second version one month later.HTML_item_4_26
  • November 1993: was published by the IETF as an Internet Draft and was a competing proposal to the Hypertext Markup Language draft. It expired in July 1994.HTML_item_4_27
  • November 1994: First draft (revision 00) of HTML 2.0 published by IETF itself (called as "HTML 2.0" from revision 02), that finally led to publication of RFC  in November 1995.HTML_item_4_28
  • April 1995 (authored March 1995): HTML 3.0 was proposed as a standard to the IETF, but the proposal expired five months later (28 September 1995) 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.HTML_item_4_29
  • W3C began development of its own Arena browser as a test bed for HTML 3 and Cascading Style Sheets, but HTML 3.0 did not succeed for several reasons. The draft was considered very large at 150 pages and the pace of browser development, as well as the number of interested parties, had outstripped the resources of the IETF. Browser vendors, including Microsoft and Netscape at the time, chose to implement different subsets of HTML 3's draft features as well as to introduce their own extensions to it. (see Browser wars). These included extensions to control stylistic aspects of documents, contrary to the "belief [of the academic engineering community] that such things as text color, background texture, font size and font face were definitely outside the scope of a language when their only intent was to specify how a document would be organized." Dave Raggett, who has been a W3C Fellow for many years, has commented for example: "To a certain extent, Microsoft built its business on the Web by extending HTML features."HTML_item_4_30

HTML_description_list_5

  • January 2008: HTML5 was published as a Working Draft by the W3C.HTML_item_5_31
  • Although its syntax closely resembles that of SGML, HTML5 has abandoned any attempt to be an SGML application and has explicitly defined its own "html" serialization, in addition to an alternative XML-based XHTML5 serialization.HTML_item_5_32
  • 2011 HTML5 – Last Call: On 14 February 2011, the W3C extended the charter of its HTML Working Group with clear milestones for HTML5. In May 2011, the working group advanced HTML5 to "Last Call", an invitation to communities inside and outside W3C to confirm the technical soundness of the specification. The W3C developed a comprehensive test suite to achieve broad interoperability for the full specification by 2014, which was the target date for recommendation. In January 2011, the WHATWG renamed its "HTML5" living standard to "HTML". The W3C nevertheless continues its project to release HTML5.HTML_item_5_33
  • 2012 HTML5 – Candidate Recommendation: In July 2012, WHATWG and W3C decided on a degree of separation. W3C will continue the HTML5 specification work, focusing on a single definitive standard, which is considered as a "snapshot" by WHATWG. The WHATWG organization will continue its work with 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.HTML_item_5_34
  • In December 2012, W3C designated HTML5 as a Candidate Recommendation. The criterion for advancement to W3C Recommendation is "two 100% complete and fully interoperable implementations".HTML_item_5_35
  • 2014 HTML5 – Proposed Recommendation and Recommendation: In September 2014, W3C moved HTML5 to Proposed Recommendation.HTML_item_5_36
  • On 28 October 2014, HTML5 was released as a stable W3C Recommendation, meaning the specification process is complete.HTML_item_5_37

XHTML versions HTML_section_8

Main article: XHTML HTML_sentence_40

XHTML is a separate language that began as a reformulation of HTML 4.01 using XML 1.0. HTML_sentence_41

It is no longer being developed as a separate standard. HTML_sentence_42

HTML_unordered_list_6

  • XHTML 1.0 was published as a W3C Recommendation on January 26, 2000, and was later revised and republished on August 1, 2002. It offers the same three variations as HTML 4.0 and 4.01, reformulated in XML, with minor restrictions.HTML_item_6_38
  • XHTML 1.1 was published as a W3C Recommendation on May 31, 2001. It is based on 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.HTML_item_6_39
  • XHTML 2.0 was a working draft, work on it was abandoned in 2009 in favor of work on HTML5 and XHTML5. XHTML 2.0 was incompatible with XHTML 1.x and, therefore, would be more accurately characterized as an XHTML-inspired new language than an update to XHTML 1.x.HTML_item_6_40
  • An XHTML syntax, known as "XHTML5.1", is being defined alongside HTML5 in the HTML5 draft.HTML_item_6_41

Transition of HTML Publication to WHATWG HTML_section_9

See also: HTML5 § W3C and WHATWG conflict HTML_sentence_43

On 28 May 2019, the W3C announced that WHATWG would be the sole publisher of the HTML and DOM standards. HTML_sentence_44

The W3C and WHATWG had been publishing competing standards since 2012. HTML_sentence_45

While the W3C standard was identical to the WHATWG in 2007 the standards have since progressively diverged due to different design decisions. HTML_sentence_46

The WHATWG "Living Standard" had been the de facto web standard for some time. HTML_sentence_47

Markup HTML_section_10

HTML markup consists of several key components, including those called tags (and their attributes), character-based data types, character references and entity references. HTML_sentence_48

HTML tags most commonly come in pairs like

and

, although some represent empty elements and so are unpaired, for example <img>. HTML_sentence_49

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). HTML_sentence_50

Another important component is the HTML document type declaration, which triggers standards mode rendering. HTML_sentence_51

The following is an example of the classic "Hello, World!" HTML_sentence_52 program: HTML_sentence_53

The text between <html> and </html> describes the web page, and the text between <body> and </body> is the visible page content. HTML_sentence_54

The markup text <title>This is a title</title> defines the browser page title, and the tag

defines a division of the page used for easy styling. HTML_sentence_55

The Document Type Declaration <!DOCTYPE html> is for HTML5. HTML_sentence_56

If a declaration is not included, various browsers will revert to "quirks mode" for rendering. HTML_sentence_57

Elements HTML_section_11

Main article: HTML element HTML_sentence_58

HTML documents imply a structure of nested HTML elements. HTML_sentence_59

These are indicated in the document by HTML tags, enclosed in angle brackets thus:

. HTML_sentence_60 In the simple, general case, the extent of an element is indicated by a pair of tags: a "start tag"

and "end tag"

. HTML_sentence_61

The text content of the element, if any, is placed between these tags. HTML_sentence_62

Tags may also enclose further tag markup between the start and end, including a mixture of tags and text. HTML_sentence_63

This indicates further (nested) elements, as children of the parent element. HTML_sentence_64

The start tag may also include attributes within the tag. HTML_sentence_65

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 in the format like this: <img src="example.com/example.jpg"> HTML_sentence_66

Some elements, such as the line break
, or
do not permit any embedded content, either text or further tags. HTML_sentence_67

These require only a single empty tag (akin to a start tag) and do not use an end tag. HTML_sentence_68

Many tags, particularly the closing end tag for the very commonly used paragraph element

, are optional. HTML_sentence_69 An 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 standard. HTML_sentence_70 These rules are complex and not widely understood by most HTML coders. HTML_sentence_71 The general form of an HTML element is therefore: <tag attribute1="value1" attribute2="value2">content</tag>. HTML_sentence_72 Some HTML elements are defined as empty elements and take the form <tag attribute1="value1" attribute2="value2">. HTML_sentence_73 Empty elements may enclose no content, for instance, the
tag or the inline <img> tag. HTML_sentence_74 The name of an HTML element is the name used in the tags. HTML_sentence_75 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. HTML_sentence_76 If attributes are not mentioned, default values are used in each case. HTML_sentence_77

Element examples HTML_section_12

See also: HTML element HTML_sentence_78

Header of the HTML document: <head>...</head>. HTML_sentence_79

The title is included in the head, for example: HTML_sentence_80

Headings: HTML headings are defined with the

to
tags with H1 being the highest (or most important) level and H6 the least: HTML_sentence_81 The Effects are: HTML_sentence_82

Heading Level 2 HTML_section_13

Heading Level 3 HTML_section_14

Heading Level 4 HTML_section_15

Note that CSS can drastically change the rendering. HTML_sentence_83

Paragraphs: HTML_sentence_84

Line breaks:
. HTML_sentence_85

The difference between
and

is that
breaks a line without altering the semantic structure of the page, whereas

sections the page into paragraphs. HTML_sentence_86 The element
is an empty element in that, although it may have attributes, it can take no content and it may not have an end tag. HTML_sentence_87 This is a link in HTML. HTML_sentence_88 To create a link the <a> tag is used. HTML_sentence_89 The href attribute holds the URL address of the link. HTML_sentence_90 Inputs: HTML_sentence_91 There are many possible ways a user can give input/s like: HTML_sentence_92 Comments: HTML_sentence_93 Comments can help in the understanding of the markup and do not display in the webpage. HTML_sentence_94 There are several types of markup elements used in HTML: HTML_sentence_95 HTML_description_list_7

  • Structural markup indicates the purpose of text: For example,

    Golf

    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).HTML_item_7_42
  • Presentational markup indicates the appearance of the text, regardless of its purpose: For example, bold text 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 bold text and italic text, there are other elements that may have equivalent visual renderings but that are more semantic in nature, such as strong text and emphasized text 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 4.0 specification in favor of using CSS for styling.HTML_item_7_43
  • 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 markup <a href="https://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="https://example.org"><img src="image.gif" alt="descriptive text" width="50" height="50" border="0"></a>.HTML_item_7_44

Attributes HTML_section_16

Main article: HTML attribute HTML_sentence_96

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. HTML_sentence_97

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). HTML_sentence_98

Leaving attribute values unquoted is considered unsafe. HTML_sentence_99

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, like the ismap attribute for the img element. HTML_sentence_100

There are several common attributes that may appear in many elements : HTML_sentence_101

HTML_unordered_list_8

  • 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.HTML_item_8_45
  • The class attribute provides a way of classifying similar elements. This can be used for semantic or presentation purposes. For example, an 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.HTML_item_8_46
  • 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.HTML_item_8_47
  • The title attribute is used to attach subtextual explanation to an element. In most browsers this attribute is displayed as a tooltip.HTML_item_8_48
  • 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:HTML_item_8_49

The abbreviation element, abbr, can be used to demonstrate some of these attributes: HTML_sentence_102

This example displays as HTML; in most browsers, pointing the cursor at the abbreviation should display the title text "Hypertext Markup Language." HTML_sentence_103

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. HTML_sentence_104

Character and entity references HTML_section_17

See also: List of XML and HTML character entity references and Unicode and HTML HTML_sentence_105

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. HTML_sentence_106

A literal character and its markup counterpart are considered equivalent and are rendered identically. HTML_sentence_107

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. HTML_sentence_108

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 an element or in the value of an attribute. HTML_sentence_109

The double-quote character ("), when not used to quote an attribute value, must also be escaped as " or " or " when it appears within the attribute value itself. HTML_sentence_110

Equivalently, the single-quote character ('), when not used to quote an attribute value, must also be escaped as ' or ' (or as ' in HTML5 or XHTML documents) when it appears within the attribute value itself. HTML_sentence_111

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. HTML_sentence_112

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. HTML_sentence_113

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. HTML_sentence_114

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 é or as the numeric references é or é, using characters that are available on all keyboards and are supported in all character encodings. HTML_sentence_115

Unicode character encodings such as UTF-8 are compatible with all modern browsers and allow direct access to almost all the characters of the world's writing systems. HTML_sentence_116

HTML_table_general_1

Example HTML Escape SequencesHTML_table_caption_1
NamedHTML_header_cell_1_0_0 DecimalHTML_header_cell_1_0_1 HexadecimalHTML_header_cell_1_0_2 ResultHTML_header_cell_1_0_3 DescriptionHTML_header_cell_1_0_4 NotesHTML_header_cell_1_0_5
&HTML_cell_1_1_0 &HTML_cell_1_1_1 &HTML_cell_1_1_2 &HTML_cell_1_1_3 AmpersandHTML_cell_1_1_4 HTML_cell_1_1_5
<HTML_cell_1_2_0 <HTML_cell_1_2_1 <HTML_cell_1_2_2 <HTML_cell_1_2_3 Less ThanHTML_cell_1_2_4 HTML_cell_1_2_5
>HTML_cell_1_3_0 >HTML_cell_1_3_1 >HTML_cell_1_3_2 >HTML_cell_1_3_3 Greater ThanHTML_cell_1_3_4 HTML_cell_1_3_5
"HTML_cell_1_4_0 "HTML_cell_1_4_1 "HTML_cell_1_4_2 "HTML_cell_1_4_3 Double QuoteHTML_cell_1_4_4 HTML_cell_1_4_5
'HTML_cell_1_5_0 'HTML_cell_1_5_1 'HTML_cell_1_5_2 'HTML_cell_1_5_3 Single QuoteHTML_cell_1_5_4 HTML_cell_1_5_5
 HTML_cell_1_6_0  HTML_cell_1_6_1  HTML_cell_1_6_2 HTML_cell_1_6_3 Non-Breaking SpaceHTML_cell_1_6_4 HTML_cell_1_6_5
©HTML_cell_1_7_0 ©HTML_cell_1_7_1 ©HTML_cell_1_7_2 ©HTML_cell_1_7_3 CopyrightHTML_cell_1_7_4 HTML_cell_1_7_5
®HTML_cell_1_8_0 ®HTML_cell_1_8_1 ®HTML_cell_1_8_2 ®HTML_cell_1_8_3 Registered TrademarkHTML_cell_1_8_4 HTML_cell_1_8_5
HTML_cell_1_9_0 HTML_cell_1_9_1 HTML_cell_1_9_2 HTML_cell_1_9_3 DaggerHTML_cell_1_9_4 HTML_cell_1_9_5
HTML_cell_1_10_0 HTML_cell_1_10_1 HTML_cell_1_10_2 HTML_cell_1_10_3 Double daggerHTML_cell_1_10_4 Names are case sensitiveHTML_cell_1_10_5
&ddagger;HTML_cell_1_11_0 HTML_cell_1_11_1 HTML_cell_1_11_2 HTML_cell_1_11_3 Double daggerHTML_cell_1_11_4 Names may have synonymsHTML_cell_1_11_5
HTML_cell_1_12_0 HTML_cell_1_12_1 HTML_cell_1_12_2 HTML_cell_1_12_3 TrademarkHTML_cell_1_12_4 HTML_cell_1_12_5

Data types HTML_section_18

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. HTML_sentence_117

All of these data types are specializations of character data. HTML_sentence_118

Document type declaration HTML_section_19

HTML documents are required to start with a Document Type Declaration (informally, a "doctype"). HTML_sentence_119

In browsers, the doctype helps to define the rendering mode—particularly whether to use quirks mode. HTML_sentence_120

The original purpose of the doctype was to enable parsing and validation of HTML documents by SGML tools based on the Document Type Definition (DTD). HTML_sentence_121

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. HTML_sentence_122

Browsers, on the other hand, do not implement HTML as an application of SGML and by consequence do not read the DTD. HTML_sentence_123

HTML5 does not define a DTD; therefore, in HTML5 the doctype declaration is simpler and shorter: HTML_sentence_124

An example of an HTML 4 doctype HTML_sentence_125

This declaration references the DTD for the "strict" version of HTML 4.01. HTML_sentence_126

SGML-based validators read the DTD in order to properly parse the document and to perform validation. HTML_sentence_127

In modern browsers, a valid doctype activates standards mode as opposed to quirks mode. HTML_sentence_128

In addition, HTML 4.01 provides Transitional and Frameset DTDs, as explained below. HTML_sentence_129

Transitional type is the most inclusive, incorporating current tags as well as older or "deprecated" tags, with the Strict DTD excluding deprecated tags. HTML_sentence_130

Frameset has all tags necessary to make frames on a page along with the tags included in transitional type. HTML_sentence_131

Semantic HTML HTML_section_20

Main article: Semantic HTML HTML_sentence_132

Semantic HTML is a way of writing HTML that emphasizes the meaning of the encoded information over its presentation (look). HTML_sentence_133

HTML has included semantic markup from its inception, but has also included presentational markup, such as , and
tags. HTML_sentence_134

There are also the semantically neutral span and div tags. HTML_sentence_135

Since the late 1990s, when Cascading Style Sheets were beginning to work in most browsers, web authors have been encouraged to avoid the use of presentational HTML markup with a view to the separation of presentation and content. HTML_sentence_136

In a 2001 discussion of the Semantic Web, 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. HTML_sentence_137

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. HTML_sentence_138

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. HTML_sentence_139

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. HTML_sentence_140

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. HTML_sentence_141

In order for search-engine spiders to be able to rate the significance of pieces of text they find in 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 need to be widely and uniformly applied to bring out the meaning of published text. HTML_sentence_142

Presentational markup tags are deprecated in current HTML and XHTML recommendations. HTML_sentence_143

The majority of presentational features from previous versions of HTML are no longer allowed as they lead to poorer accessibility, higher cost of site maintenance, and larger document sizes. HTML_sentence_144

Good semantic HTML also improves the accessibility of web documents (see also Web Content Accessibility Guidelines). HTML_sentence_145

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. HTML_sentence_146

Delivery HTML_section_21

HTML documents can be delivered by the same means as any other computer file. HTML_sentence_147

However, they are most often delivered either by HTTP from a web server or by email. HTML_sentence_148

HTTP HTML_section_22

Main article: Hypertext Transfer Protocol HTML_sentence_149

The World Wide Web is composed primarily of HTML documents transmitted from web servers to web browsers using the Hypertext Transfer Protocol (HTTP). HTML_sentence_150

However, HTTP is used to serve images, sound, and other content, in addition to HTML. HTML_sentence_151

To allow the web browser to know how to handle each document it receives, other information is transmitted along with the document. HTML_sentence_152

This meta data usually includes the MIME type (e.g., text/html or application/xhtml+xml) and the character encoding (see Character encoding in HTML). HTML_sentence_153

In modern browsers, the MIME type that is sent with the HTML document may affect how the document is initially interpreted. HTML_sentence_154

A document sent with the XHTML MIME type is expected to be well-formed XML; syntax errors may cause the browser to fail to render it. HTML_sentence_155

The same document sent with the HTML MIME type might be displayed successfully, since some browsers are more lenient with HTML. HTML_sentence_156

The W3C recommendations state that XHTML 1.0 documents that follow guidelines set forth in the recommendation's Appendix C may be labeled with either MIME Type. HTML_sentence_157

XHTML 1.1 also states that XHTML 1.1 documents should be labeled with either MIME type. HTML_sentence_158

HTML e-mail HTML_section_23

Main article: HTML email HTML_sentence_159

Most graphical email clients allow the use of a subset of HTML (often ill-defined) to provide formatting and semantic markup not available with plain text. HTML_sentence_160

This may include typographic information like coloured headings, emphasized and quoted text, inline images and diagrams. HTML_sentence_161

Many such clients include both a GUI editor for composing HTML e-mail messages and a rendering engine for displaying them. HTML_sentence_162

Use of 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. HTML_sentence_163

Naming conventions HTML_section_24

The most common for containing HTML is .html. HTML_sentence_164

A common abbreviation of this is .htm, which originated because some early operating systems and file systems, such as DOS and the limitations imposed by data structure, limited file extensions to . HTML_sentence_165

HTML Application HTML_section_25

Main article: HTML Application HTML_sentence_166

An HTML Application (HTA; file extension ".hta") is a Microsoft Windows application that uses HTML and Dynamic HTML in a browser to provide the application's graphical interface. HTML_sentence_167

A regular HTML file is confined to the security model of the web browser's security, communicating only to web servers and manipulating only web page objects and site cookies. HTML_sentence_168

An HTA runs as a fully trusted application and therefore has more privileges, like creation/editing/removal of files and Windows Registry entries. HTML_sentence_169

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. HTML_sentence_170

HTML4 variations HTML_section_26

Since its inception, HTML and its associated protocols gained acceptance relatively quickly. HTML_sentence_171

However, no clear standards existed in the early years of the language. HTML_sentence_172

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. HTML_sentence_173

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. HTML_sentence_174

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. HTML_sentence_175

In conjunction, the HTML specification has slowly reined in the presentational elements. HTML_sentence_176

There are two axes differentiating various variations of HTML as currently specified: SGML-based HTML versus XML-based HTML (referred to as XHTML) on one axis, and strict versus transitional (loose) versus frameset on the other axis. HTML_sentence_177

SGML-based versus XML-based HTML HTML_section_27

One difference in the latest HTML specifications lies in the distinction between the SGML-based specification and the XML-based specification. HTML_sentence_178

The XML-based specification is usually called XHTML to distinguish it clearly from the more traditional definition. HTML_sentence_179

However, the root element name continues to be "html" even in the XHTML-specified HTML. HTML_sentence_180

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. HTML_sentence_181

Because XHTML and HTML are closely related, they are sometimes documented in parallel. HTML_sentence_182

In such circumstances, some authors conflate the two names as (X)HTML or X(HTML). HTML_sentence_183

Like HTML 4.01, XHTML 1.0 has three sub-specifications: strict, transitional and frameset. HTML_sentence_184

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. HTML_sentence_185

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. HTML_sentence_186

By contrast, XHTML requires all elements to have an opening tag and a closing tag. HTML_sentence_187

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:
. HTML_sentence_188

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. HTML_sentence_189

A fix for this is to include a space before closing the tag, as such:
. HTML_sentence_190

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. HTML_sentence_191

To make this translation requires the following steps: HTML_sentence_192

HTML_ordered_list_9

  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.HTML_item_9_50
  2. Remove the XML namespace (xmlns=URI). HTML has no facilities for namespaces.HTML_item_9_51
  3. Change the document type declaration from XHTML 1.0 to HTML 4.01. (see DTD section for further explanation).HTML_item_9_52
  4. If present, remove the XML declaration. (Typically this is: <?xml version="1.0" encoding="utf-8"?>).HTML_item_9_53
  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.HTML_item_9_54
  6. Change the XML empty-element syntax to an HTML style empty element (
    to
    ).HTML_item_9_55

Those are the main changes necessary to translate a document from XHTML 1.0 to HTML 4.01. HTML_sentence_193

To translate from HTML to XHTML would also require the addition of any omitted opening or closing tags. HTML_sentence_194

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. HTML_sentence_195

A well-formed XHTML document adheres to all the syntax requirements of XML. HTML_sentence_196

A valid document adheres to the content specification for XHTML, which describes the document structure. HTML_sentence_197

The W3C recommends several conventions to ensure an easy migration between HTML and XHTML (see ). HTML_sentence_198

The following steps can be applied to XHTML 1.0 documents only: HTML_sentence_199

HTML_unordered_list_10

  • Include both xml:lang and lang attributes on any elements assigning language.HTML_item_10_56
  • Use the empty-element syntax only for elements specified as empty in HTML.HTML_item_10_57
  • Include an extra space in empty-element tags: for example
    instead of
    .HTML_item_10_58
  • Include explicit close tags for elements that permit content but are left empty (for example,
    , not
    ).HTML_item_10_59
  • Omit the XML declaration.HTML_item_10_60

By carefully following the W3C's compatibility guidelines, a user agent should be able to interpret the document equally as HTML or XHTML. HTML_sentence_200

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). HTML_sentence_201

When delivered as XHTML, browsers should use an XML parser, which adheres strictly to the XML specifications for parsing the document's contents. HTML_sentence_202

Transitional versus strict HTML_section_28

HTML 4 defined three different versions of the language: Strict, Transitional (once called Loose) and Frameset. HTML_sentence_203

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 specification or didn't conform to any specification to a version of HTML 4. HTML_sentence_204

The Transitional and Frameset versions allow for presentational markup, which is omitted in the Strict version. HTML_sentence_205

Instead, cascading style sheets are encouraged to improve the presentation of HTML documents. HTML_sentence_206

Because XHTML 1 only defines an XML syntax for the language defined by HTML 4, the same differences apply to XHTML 1 as well. HTML_sentence_207

The Transitional version allows the following parts of the vocabulary, which are not included in the Strict version: HTML_sentence_208

HTML_unordered_list_11

  • A looser content modelHTML_item_11_61
    • Inline elements and plain text are allowed directly in: body, blockquote, form, noscript and noframesHTML_item_11_62
  • Presentation related elementsHTML_item_11_63
    • underline (u)(Deprecated. can confuse a visitor with a hyperlink.)HTML_item_11_64
    • strike-through (s)HTML_item_11_65
    • center (Deprecated. use CSS instead.)HTML_item_11_66
    • font (Deprecated. use CSS instead.)HTML_item_11_67
    • basefont (Deprecated. use CSS instead.)HTML_item_11_68
  • Presentation related attributesHTML_item_11_69
    • background (Deprecated. use CSS instead.) and bgcolor (Deprecated. use CSS instead.) attributes for body (required element according to the W3C.) element.HTML_item_11_70
    • align (Deprecated. use CSS instead.) attribute on div, form, paragraph (p) and heading (h1...h6) elementsHTML_item_11_71
    • align (Deprecated. use CSS instead.), noshade (Deprecated. use CSS instead.), size (Deprecated. use CSS instead.) and width (Deprecated. use CSS instead.) attributes on hr elementHTML_item_11_72
    • align (Deprecated. use CSS instead.), border, vspace and hspace attributes on img and object (caution: the object element is only supported in Internet Explorer (from the major browsers)) elementsHTML_item_11_73
    • align (Deprecated. use CSS instead.) attribute on legend and caption elementsHTML_item_11_74
    • align (Deprecated. use CSS instead.) and bgcolor (Deprecated. use CSS instead.) on table elementHTML_item_11_75
    • nowrap (Obsolete), bgcolor (Deprecated. use CSS instead.), width, height on td and th elementsHTML_item_11_76
    • bgcolor (Deprecated. use CSS instead.) attribute on tr elementHTML_item_11_77
    • clear (Obsolete) attribute on br elementHTML_item_11_78
    • compact attribute on dl, dir and menu elementsHTML_item_11_79
    • type (Deprecated. use CSS instead.), compact (Deprecated. use CSS instead.) and start (Deprecated. use CSS instead.) attributes on ol and ul elementsHTML_item_11_80
    • type and value attributes on li elementHTML_item_11_81
    • width attribute on pre elementHTML_item_11_82
  • Additional elements in Transitional specificationHTML_item_11_83
    • menu (Deprecated. use CSS instead.) list (no substitute, though unordered list is recommended)HTML_item_11_84
    • dir (Deprecated. use CSS instead.) list (no substitute, though unordered list is recommended)HTML_item_11_85
    • 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)HTML_item_11_86
    • applet (Deprecated. use the object element instead.)HTML_item_11_87
  • The language (Obsolete) attribute on script element (redundant with the type attribute).HTML_item_11_88
  • Frame related entitiesHTML_item_11_89
    • iframeHTML_item_11_90
    • noframesHTML_item_11_91
    • target (Deprecated in the map, link and form elements.) attribute on a, client-side image-map (map), link, form and base elementsHTML_item_11_92

The Frameset version includes everything in the Transitional version, as well as the frameset element (used instead of body) and the frame element. HTML_sentence_209

Frameset versus transitional HTML_section_29

In addition to the above transitional differences, the frameset specifications (whether XHTML 1.0 or HTML 4.01) specify a different content model, with frameset replacing body, that contains either frame elements, or optionally noframes with a body. HTML_sentence_210

Summary of specification versions HTML_section_30

As this list demonstrates, the loose versions of the specification are maintained for legacy support. HTML_sentence_211

However, contrary to popular misconceptions, the move to XHTML does not imply a removal of this legacy support. HTML_sentence_212

Rather the X in XML stands for extensible and the W3C is modularizing the entire specification and opening it up to independent extensions. HTML_sentence_213

The primary achievement in the move from XHTML 1.0 to XHTML 1.1 is the modularization of the entire specification. HTML_sentence_214

The strict version of HTML is deployed in XHTML 1.1 through a set of modular extensions to the base XHTML 1.1 specification. HTML_sentence_215

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). HTML_sentence_216

The modularization also allows for separate features to develop on their own timetable. HTML_sentence_217

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. HTML_sentence_218

In summary, the HTML 4 specification primarily reined in all the various HTML implementations into a single clearly written specification based on SGML. HTML_sentence_219

XHTML 1.0, ported this specification, as is, to the new XML defined specification. HTML_sentence_220

Next, XHTML 1.1 takes advantage of the extensible nature of XML and modularizes the whole specification. HTML_sentence_221

XHTML 2.0 was intended to be the first step in adding new features to the specification in a standards-body-based approach. HTML_sentence_222

WHATWG HTML versus HTML5 HTML_section_31

Main article: § Transition_of_HTML_Publication_to_WHATWG HTML_sentence_223

The HTML Living Standard, which is developed by WHATWG, is the official version, while W3C HTML5 is no longer separate from WHATWG. HTML_sentence_224

WYSIWYG editors HTML_section_32

There are some 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. HTML_sentence_225

The editor renders the document rather than show the code, so authors do not require extensive knowledge of HTML. HTML_sentence_226

The WYSIWYG editing model has been criticized, primarily because of the low quality of the generated code; there are voices advocating a change to the WYSIWYM model (What You See Is What You Mean). HTML_sentence_227

WYSIWYG editors remain a controversial topic because of their perceived flaws such as: HTML_sentence_228

HTML_unordered_list_12

  • Relying mainly on layout as opposed to meaning, often using markup that does not convey the intended meaning but simply copies the layout.HTML_item_12_93
  • Often producing extremely verbose and redundant code that fails to make use of the cascading nature of HTML and CSS.HTML_item_12_94
  • Often producing ungrammatical markup, called tag soup or semantically incorrect markup (such as for italics).HTML_item_12_95
  • As a great deal of the information in HTML documents is not in the layout, the model has been criticized for its "what you see is all you get"-nature.HTML_item_12_96

See also HTML_section_33

Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/HTML.