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History of HTML

Development

Tim Berners-Lee in April 2009

In 1980, physicist Tim Berners-Lee, a contractor at CERN, proposed and prototyped ENQUIRE, a system for CERN researchers to use and share documents. In 1989, Berners-Lee wrote a memo proposing an Internet-based hypertext system.^[3] Berners-Lee specified HTML and wrote the browser and server software in late 1990. 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. In his personal notes^[4] from 1990 he listed^[5] “some of the many areas in which hypertext is used” and put an encyclopedia first.

The first publicly available description of HTML was a document called “HTML Tags”, first mentioned on the Internet by Tim Berners-Lee in late 1991.^[6][7] 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 4.^[8]

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 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 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.

Berners-Lee considered HTML to be an application of SGML. 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.^[9][10] 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. 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.^[11]

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.^[12]

Further development under the auspices of the IETF was stalled by competing interests. Since 1996, the HTML specifications have been maintained, with input from commercial software vendors, by the World Wide Web Consortium (W3C).^[13] However, in 2000, HTML also became an international standard (ISO/IEC 15445:2000). HTML 4.01 was published in late 1999, with further errata published through 2001. 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.^[14]

HTML versions timeline

HTML 2

November 24, 1995HTML 2.0 was published as RFC1866. 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)

HTML 3

January 14, 1997HTML 3.2^[15] 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.^[16]Initially code-named “Wilbur”,^[17] 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.^[13] A markup for mathematical formulas similar to that in HTML was not standardized until 14 months later in MathML.

HTML 4

December 18, 1997HTML 4.0^[18] was published as a 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”,^[17] 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.^[19]April 24, 1998HTML 4.0^[20] was reissued with minor edits without incrementing the version number.December 24, 1999HTML 4.01^[21] was published as a W3C Recommendation. It offers the same three variations as HTML 4.0 and its last errata were published on May 12, 2001.May 2000ISO/IEC 15445:2000^[22][23] (“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).^[22]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 5

Main article: HTML5October 28, 2014HTML5^[24] was published as a W3C Recommendation.^[25]November 1, 2016HTML 5.1^[26] was published as a W3C Recommendation.^[27][28]December 14, 2017HTML 5.2^[29] was published as a W3C Recommendation.^[30][31]

HTML draft version timeline

October 1991HTML Tags,^[6] an informal CERN document listing 18 HTML tags, was first mentioned in public.June 1992First informal draft of the HTML DTD,^[32] with seven^[33][34][35] subsequent revisions (July 15, August 6, August 18, November 17, November 19, November 20, November 22)November 1992HTML 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^[35]June 1993Hypertext Markup Language^[36] 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^[37] one month later.November 1993HTML+ 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.^[38]November 1994First draft (revision 00) of HTML 2.0 published by IETF itself^[39] (called as “HTML 2.0” from revision 02^[40]), that finally led to publication of RFC1866 in November 1995.^[41]April 1995 (authored March 1995)HTML 3.0^[42] was proposed as a standard to the IETF, but the proposal expired five months later (28 September 1995)^[43] 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.^[43]W3C began development of its own Arena browser as a test bed for HTML 3 and Cascading Style Sheets,^[44][45][46] 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.^[13] 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.^[13] (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.”^[13] 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.”^[13]Logo of HTML5January 2008HTML5 was published as a Working Draft by the W3C.^[47]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.^[48]2011 HTML5 – Last CallOn 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.^[49] In January 2011, the WHATWG renamed its “HTML5” living standard to “HTML”. The W3C nevertheless continues its project to release HTML5.^[50]2012 HTML5 – Candidate RecommendationIn 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.^[51]In December 2012, W3C designated HTML5 as a Candidate Recommendation.^[52] The criterion for advancement to W3C Recommendation is “two 100% complete and fully interoperable implementations”.^[53]2014 HTML5 – Proposed Recommendation and RecommendationIn September 2014, W3C moved HTML5 to Proposed Recommendation.^[54]On 28 October 2014, HTML5 was released as a stable W3C Recommendation,^[55] meaning the specification process is complete.^[56]

XHTML versions

Main article: XHTML

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

• XHTML 1.0 was published as a W3C Recommendation on January 26, 2000,^[57] 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.
• XHTML 1.1^[58] 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.^[59]
• XHTML 2.0 was a working draft, work on it was abandoned in 2009 in favor of work on HTML5 and XHTML5.^[60][61][62] 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.
• An XHTML syntax, known as “XHTML5.1”, is being defined alongside HTML5 in the HTML5 draft.^[63]

Transition of HTML Publication to WHATWG

See also: HTML5 § W3C and WHATWG conflict

On 28 May 2019, the W3C announced that WHATWG would be the sole publisher of the HTML and DOM standards.^{[64][65][66][67]} The W3C and WHATWG had been publishing competing standards since 2012. While the W3C standard was identical to the WHATWG in 2007 the standards have since progressively diverged due to different design decisions.^[68] The WHATWG “Living Standard” had been the de facto web standard for some time.^[69]

Markup

HTML markup consists of several key components, including those called tags (and their attributes), character-based data types, character references and entity references. 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 document type declaration, which triggers standards mode rendering.

The following is an example of the classic “Hello, World!” program:

<!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.^[70]

Elements

Main article: HTML element

HTML documents imply a structure of nested HTML elements. These are indicated in the document by HTML tags, enclosed in angle brackets thus: <p>.^{[71][better source needed]}

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 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. These rules are complex and not widely understood by most HTML coders.

The general form of an HTML element is therefore: <tag attribute1="value1" attribute2="value2">''content''</tag>. Some 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 document: <head>...</head>. The title is included in the head, for example:

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

Headings: HTML headings are defined with the <h1> to <h6> tags with H1 being the highest (or most important) level and H6 the least:

<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 1</p> <p>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. The element 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 textFor 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).^[72]Presentational markup indicates the appearance of the text, regardless of its purposeFor 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>emphasized 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 4.0 specification in favor of using CSS for styling.Hypertext markup makes parts of a document into links to other documentsAn 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 “Wikipedia” 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>.

Attributes

Main article: 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 (but not XHTML).^[73][74] Leaving attribute values unquoted is considered unsafe.^[75] 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,^[6] like the ismap attribute for the img element.^[76]

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 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 Markup Language">HTML</abbr>

This example displays as HTML; in most browsers, pointing the cursor at the abbreviation should display the title text “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.^[77]

Character and entity references

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

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

The ability to “escape” characters in this way allows for the characters < and & (when written as < and &, respectively) to be interpreted as character data, rather than markup. For example, a literal < normally indicates the start of a tag, and & normally indicates the start of a character entity reference or numeric character reference; writing it as & or & or & allows & to be included in the content of 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 " or " or " 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 ' or ' (or as ' in HTML5 or XHTML documents^[78][79]) 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 é or as the numeric references é or é, using characters that are available on all keyboards and are supported in all character encodings. 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.^[80]

Data types

HTML defines several data types for element content, such as script data and stylesheet data, and a plethora of types for attribute values, including IDs, names, URIs, numbers, units of length, languages, media descriptors, colors, character encodings, dates and times, and so on. All of these data types are specializations of character data.

Document type declaration

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 documents by 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 as an application of SGML and by consequence do not read the DTD.

HTML5 does not define a DTD; therefore, in HTML5 the doctype declaration is simpler and shorter:^[81]

<!DOCTYPE html>

An example of an HTML 4 doctype

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "https://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 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 that emphasizes the meaning of the encoded information over its presentation (look). HTML has included semantic markup from its inception,^[82] 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 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.^[83]

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.^[84] 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 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.^[85]

Presentational markup tags are deprecated in current HTML and XHTML recommendations. 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.^[86]

Good semantic HTML also improves the accessibility of web documents (see also Web Content 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 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 Transfer Protocol

The World Wide Web is composed primarily of HTML documents transmitted from web servers to web browsers using the 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 in HTML).

In modern browsers, the MIME type that is sent with the HTML document may affect how the document is initially interpreted. 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. The same document sent with the HTML MIME type might be displayed successfully, since some browsers are more lenient with HTML.

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.^[87] XHTML 1.1 also states that XHTML 1.1 documents should^[88] be labeled with either MIME type.^[89]

HTML e-mail

Main article: HTML email

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. 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 e-mail messages and a rendering engine for displaying them. 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.

Naming conventions

The most common filename extension for files containing HTML is .html. 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 FAT data structure, limited file extensions to three letters.^[90]

HTML Application

Main article: HTML Application

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. 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. An HTA runs as a fully trusted application and therefore has more privileges, like creation/editing/removal of files and 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 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 as a semantic language devoid of presentation details,^[91] practical uses pushed many presentational elements and attributes into the language, driven largely by the various browser vendors. The latest standards surrounding HTML reflect efforts to overcome the sometimes chaotic development of the language^[92] and to create a rational foundation for building both meaningful and well-presented documents. To return HTML to its role as a semantic language, the W3C has developed style languages such as CSS and XSL to shoulder the burden of presentation. In conjunction, the HTML specification has slowly reined in the presentational elements.

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.

SGML-based versus XML-based HTML

One difference in the latest HTML specifications lies in the distinction between the SGML-based specification and the XML-based specification. The XML-based specification is usually called XHTML to distinguish it clearly from the more traditional definition. However, the root element name continues to be “html” even in the XHTML-specified HTML. The W3C intended XHTML 1.0 to be identical to HTML 4.01 except where limitations of XML over the more complex SGML require workarounds. Because XHTML and HTML are closely related, they are sometimes documented in parallel. In such circumstances, some authors conflate the two names as (X)HTML or X(HTML).

Like HTML 4.01, 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 4.01 and XHTML 1.0 document—in each of the corresponding DTDs—are largely syntactic. The underlying syntax of HTML allows many shortcuts that XHTML does not, such as elements with optional opening or closing tags, and even empty elements which must not have an end tag. By contrast, XHTML requires all elements to have an opening tag and a closing tag. XHTML, however, also introduces a new shortcut: an XHTML tag may be opened and closed within the same tag, by including a slash before the end of the tag like this: <br/>. The introduction of this shorthand, which is not used in the SGML declaration for HTML 4.01, may confuse earlier software unfamiliar with this new convention. A fix for this is to include a space before closing the tag, as such: <br />.^[93]

To understand the subtle differences between HTML and XHTML, consider the transformation of a valid and well-formed XHTML 1.0 document that adheres to Appendix C (see below) into a valid HTML 4.01 document. To make this translation requires the following steps:

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

Those are the main changes necessary to translate a document from XHTML 1.0 to HTML 4.01. To translate from HTML to XHTML would also require the addition of any omitted opening or closing tags. Whether coding in HTML or XHTML it may just be best to always include the optional tags within an HTML document rather than remembering which tags can be omitted.

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

The W3C recommends several conventions to ensure an easy migration between HTML and XHTML (see HTML Compatibility Guidelines). The following steps can be applied to XHTML 1.0 documents only:

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

By carefully following the W3C’s compatibility guidelines, a user agent should be able to interpret the document equally as HTML or XHTML. For documents that are XHTML 1.0 and have been made compatible in this way, the W3C permits them to be served either as HTML (with a text/html MIME type), or as XHTML (with an application/xhtml+xml or application/xml MIME type). When delivered as XHTML, browsers should use an XML parser, which adheres strictly to the XML specifications for parsing the document’s contents.

Transitional versus strict

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 specification or didn’t conform to any specification to a version of 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 documents. Because XHTML 1 only defines an XML syntax for the language defined by HTML 4, the same differences apply to 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 instead.)
  • font (Deprecated. use CSS instead.)
  • basefont (Deprecated. use CSS instead.)
• Presentation related attributes
  • background (Deprecated. use CSS instead.) and bgcolor (Deprecated. use CSS instead.) attributes for body (required element according to the W3C.) element.
  • align (Deprecated. use CSS instead.) attribute on div, form, paragraph (p) and heading (h1…h6) elements
  • align (Deprecated. use CSS instead.), noshade (Deprecated. use CSS instead.), size (Deprecated. use CSS instead.) and width (Deprecated. use CSS instead.) attributes on hr element
  • 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)) elements
  • align (Deprecated. use CSS instead.) attribute on legend and caption elements
  • align (Deprecated. use CSS instead.) and bgcolor (Deprecated. use CSS instead.) on table element
  • nowrap (Obsolete), bgcolor (Deprecated. use CSS instead.), width, height on td and th elements
  • bgcolor (Deprecated. use CSS instead.) attribute on tr element
  • clear (Obsolete) attribute on br element
  • compact attribute on dl, dir and menu elements
  • type (Deprecated. use CSS instead.), compact (Deprecated. use CSS instead.) and start (Deprecated. use 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 instead.) list (no substitute, though unordered list is recommended)
  • dir (Deprecated. use 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 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.

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 does not imply a removal of this legacy support. Rather the X in XML stands for extensible and the W3C is modularizing the entire specification and opening it up to independent extensions. The primary achievement in the move from XHTML 1.0 to XHTML 1.1 is the modularization of the entire specification. The strict version of HTML is deployed in XHTML 1.1 through a set of modular extensions to the base XHTML 1.1 specification. Likewise, someone looking for the loose (transitional) or frameset specifications will find similar extended XHTML 1.1 support (much of it is contained in the legacy or frame modules). The modularization also allows for separate features to develop on their own timetable. So for example, XHTML 1.1 will allow quicker migration to emerging XML standards such as MathML (a presentational and semantic math language based on XML) and XForms—a new highly advanced web-form technology to replace the existing HTML forms.

In summary, the HTML 4 specification primarily reined in all the various HTML implementations into a single clearly written specification based on SGML. XHTML 1.0, ported this specification, as is, to the new XML defined specification. Next, XHTML 1.1 takes advantage of the extensible nature of XML and modularizes the whole specification. XHTML 2.0 was intended to be the first step in adding new features to the specification in a standards-body-based approach.

WHATWG HTML versus HTML5

Main article: § Transition_of_HTML_Publication_to_WHATWG

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

Hypertext features not in HTML

HTML lacks some of the features found in earlier hypertext systems, such as source tracking, fat links and others.^[94] Even some hypertext features that were in early versions of HTML have been ignored by most popular web browsers until recently,^[when?] such as the link element and in-browser 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.

HTML element

From Wikipedia, the free encyclopediaJump to navigationJump to searchThis article is about the HTML elements in general. For information on how to format Wikipedia entries, see Help:Wiki markup and Help:HTML in wikitext.”nobr” redirects here. For the chemical compound NOBr, see Nitrosyl bromide.

HTML
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Comparisons
Document markup languagesHTML supportXHTML 1.1

An HTML element is a type of HTML (Hypertext Markup Language) document component, one of several types of HTML nodes (there are also text nodes, comment nodes and others).^[vague] HTML document is composed of a tree of simple HTML nodes, such as text nodes, and HTML elements, which add semantics and formatting to parts of document (e.g., make text bold, organize it into paragraphs, lists and tables, or embed hyperlinks and images). Each element can have HTML attributes specified. Elements can also have content, including other elements and text.

Concepts[edit]

Document vs. DOM[edit]

HTML documents are delivered as “documents”.^{[note 1]} These are then parsed, which turns them into the Document Object Model (DOM) internal representation, within the web browser.^{[note 2][note 3]} Presentation by the web browser (such as screen rendering or access by JavaScript) is then performed on this internal DOM, not the original document.

Early HTML documents (and to a lesser extent today’s HTML documents) were largely invalid HTML and riddled with syntax errors. The parsing process was also required to “fix” these errors as best it could. The result was often not correct (i.e., it did not represent what a careless coder had originally intended) but was at least valid according to the HTML standard. Only in the rarest cases would the parser abandon parsing altogether.

Elements vs. tags[edit]

As is generally understood, the position of an element is indicated as spanning from a start tag, possibly including some child content, and is terminated by an end tag.^[3] This is the case for many, but not all, elements within an HTML document. The distinction is explicitly emphasised in HTML 4.01 Specification:

Elements are not tags. Some people refer to elements as tags (e.g., “the P tag”). Remember that the element is one thing, and the tag (be it start or end tag) is another. For instance, the HEAD element is always present, even though both start and end HEAD tags may be missing in the markup.^[3]

Similarly the W3C Recommendadtion HTML 5.1 2nd Edition explicitly says:

Tags are used to delimit the start and end of elements in the markup. (…) The start and end tags of certain normal elements can be omitted, (…)
The contents of the element must be placed between just after the start tag (which might be implied, in certain cases) and just before the end tag (which again, might be implied, in certain cases).— HTML 5.1 2nd Edition § 8.1.2. Elements § Tags

and:

Certain tags can be omitted.
NOTE:
Omitting an element’s start tag (…) does not mean the element is not present; it is implied, but it is still there. For example, an HTML document always has a root <html> element, even if the string <html> doesn’t appear anywhere in the markup.— HTML 5.1 2nd Edition § 8.1.2.4. Optional tags

As HTML (before HTML5) is based on SGML,^[4] its parsing also depends on the Document Type Definition (DTD), specifically an HTML DTD (e.g. HTML 4.01^{[5][note 4]}). The DTD specifies which element types are possible (i.e. it defines the set of element types) and also the valid combinations in which they may appear in a document. It is part of general SGML behavior that, where only one valid structure is possible (per the DTD), its explicit statement in any given document is not generally required. As a simple example, the <p> tag indicating the start of a paragraph element should be complemented by a </p> tag indicating its end. But since the DTD states that paragraph elements cannot be nested, an HTML document fragment <p>Para 1 <p>Para 2 <p>Para 3is thus inferred to be equivalent to <p>Para 1 </p><p>Para 2 </p><p>Para 3. (If one paragraph element cannot contain another, any currently open paragraph must be closed before starting another.) Because this implication is based on the combination of the DTD and the individual document, it is not usually possible to infer elements from document tags alone but only by using an SGML—or HTML—aware parser with knowledge of the DTD. HTML5 creates a similar result by defining what tags can be omitted.^[6]

SGML vs. XML[edit]

SGML is complex, which has limited its widespread understanding and adoption. XML was developed as a simpler alternative. Although both can use the DTD to specify the supported elements and their permitted combinations as document structure, XML parsing is simpler. The relation from tags to elements is always that of parsing the actual tags included in the document, without the implied closures that are part of SGML.^{[note 5]}

HTML as used on the current web is likely to be either treated as XML, by being XHTML, or as HTML5; in either case the parsing of document tags into DOM elements is simplified compared to legacy HTML systems. Once the DOM of elements is obtained, behavior at higher levels of interface (example: screen rendering) is identical or nearly so.^{[note 6]}

%block; vs. box[edit]

Part of this CSS presentation behavior is the notion of the “box model“. This is applied to those elements that CSS considers to be “block” elements, set through the CSS display: block; declaration.

HTML also has a similar concept, although different, and the two are very frequently confused. %block; and %inline; are groups within the HTML DTD that group elements as being either “block-level” or “inline”.^[8] This is used to define their nesting behavior: block-level elements cannot be placed into an inline context.^{[note 7]} This behavior cannot be changed; it is fixed in the DTD. Block and inline elements have the appropriate and different CSS behaviors attached to them by default,^[8] including the relevance of the box model for particular element types.

Note though that this CSS behavior can, and frequently is, changed from the default. Lists with <ul><li> ... are %block; elements and are presented as block elements by default. However, it is quite common to set these with CSS to display as an inline list.^[9]

Overview[edit]

Syntax[edit]

{\displaystyle \overbrace {\overbrace {{\mathtt {\color {BrickRed}<\!p\ }}\color {Magenta}\underbrace {\mathtt {class}} _{\mathsf {\color {Black}{Attribute \atop name}}}{\mathtt {=”}}\!\underbrace {\mathtt {paragraph}} _{\mathsf {\color {White}{Attr} \atop \color {Black}Attribute\ value}}”{\mathtt {\color {BrickRed}>}}} ^{\mathsf {Start\ tag}}\overbrace {\mathtt {\color {Green}This\ is\ a\ paragraph.}} ^{\mathsf {Content}}\overbrace {\mathtt {\color {BrickRed}<\!/p\!>}} ^{\mathsf {End \atop tag}}} ^{\mathsf {Element}}}<img src=”https://wikimedia.org/api/rest_v1/media/math/render/svg/37506127f0730d9b6035530f46c706af4e2319d4&#8243; alt=”{\displaystyle \overbrace {\overbrace {{\mathtt {\color {BrickRed}}}} ^{\mathsf {Start\ tag}}\overbrace {\mathtt {\color {Green}This\ is\ a\ paragraph.}} ^{\mathsf {Content}}\overbrace {\mathtt {\color {BrickRed}}} ^{\mathsf {End \atop tag}}} ^{\mathsf {Element}}}”>Parts of an HTML container element

In the HTML syntax, most elements are written with a start tag and an end tag, with the content in between. An HTML tag is composed of the name of the element, surrounded by angle brackets. An end tag also has a slash after the opening angle bracket, to distinguish it from the start tag. For example, a paragraph, which is represented by the <p> element, would be written as:

<p>In the HTML syntax, most elements are written ...</p>

However, not all of these elements require the end tag, or even the start tag, to be present.^[6] Some elements, the so-called void elements, do not have an end tag. A typical example is the <br> (hard line-break) element. A void element’s behavior is predefined, and it cannot contain any content or other elements. For example, an address would be written as:

<p>P. Sherman<br>42 Wallaby Way<br>Sydney</p>

When using XHTML, it is required to open and close all elements, including void elements. This can be done by placing an end tag immediately after the start tag, but this is not legal in HTML 5 and will lead to two elements being created. An alternative way to specify that it is a void element, which is compatible with both XHTML and HTML 5, is to put a / at the end of the tag (not to be confused with the / at the beginning of a closing tag).

<p>P. Sherman<br />42 Wallaby Way<br />Sydney</p>

HTML attributes are specified inside the start tag. For example, the <abbr> element, which represents an abbreviation, expects a title attribute within its opening tag. This would be written as:

<abbr title="abbreviation">abbr.</abbr>

There are multiple kinds of HTML elements: void elements, raw text elements, and normal elements.

Void elements (also sometimes called empty elements, single elements or stand-alone elements) only have a start tag (in the form <tag>), which contains any HTML attributes. They may not contain any children, such as text or other elements. For compatibility with XHTML, the HTML specification allows an optional space and slash (<tag /> is permissible). The space and slash are required in XHTML and other XML applications. Two common void elements are <br /> (for a hard line-break, such as in a poem or an address) and <hr /> (for a thematic break). Other such elements are often place-holders which reference external files, such as the image (<img />) element. The attributes included in the element will then point to the external file in question. Another example of a void element is <link />, for which the syntax is:

<link rel="stylesheet" href="fancy.css" type="text/css">

This <link /> element points the browser at a style sheet to use when presenting the HTML document to the user. Note that in the HTML syntax attributes don’t have to be quoted if they are composed only of certain characters: letters, digits, the hyphen-minus and the full stop. When using the XML syntax (XHTML), on the other hand, all attributes must be quoted, and a spaced trailing slash is required before the last angle bracket:

<link rel="stylesheet" href="fancy.css" type="text/css" />

Raw text elements (also known as text or text-only elements) are constructed with:

• a start tag (in the form <tag>) marking the beginning of an element, which may incorporate any number of HTML attributes;
• some amount of text content, but no elements (all tags, apart from the applicable end tag, will be interpreted as content);
• an end tag, in which the element name is prefixed with a slash: </tag>. In some versions of HTML, the end tag is optional for some elements. The end tag is required in XHTML.

An example is the <title> element must not contain other elements (including markup of text), only plain text.

Normal elements usually have both a start tag and an end tag, although for some elements the end tag, or both tags, can be omitted. It is constructed in a similar way:

• a start tag (<tag>) marking the beginning of an element, which may incorporate any number of HTML attributes;
• some amount of content, including text and other elements;
• an end tag, in which the element name is prefixed with a slash: </tag>.

HTML attributes define desired behavior or indicate additional element properties. Most attributes require a value. In HTML, the value can be left unquoted if it does not include spaces (attribute=value), or it can be quoted with single or double quotes (attribute='value' or attribute="value"). In XML, those quotes are required.

Boolean attributes, on the other hand, don’t require a value to be specified. An example is the checked for checkboxes:

<input type=checkbox checked>

In the XML (and thus XHTML) syntax, though, the name should be repeated as the value:

<input type="checkbox" checked="checked" />

Informally, HTML elements are sometimes referred to as “tags” (an example of synecdoche), though many prefer the term tag strictly in reference to the markup delimiting the start and end of an element.

Element (and attribute) names may be written in any combination of upper or lower case in HTML, but must be in lower case in XHTML.^[10] The canonical form was upper-case until HTML 4, and was used in HTML specifications, but in recent years, lower-case has become more common.

Element standards[edit]

HTML elements are defined in a series of freely available open standards issued since 1995, initially by the IETF and subsequently by the W3C.

During the browser wars of the 1990s, developers of user agents (e.g. web browsers) often developed their own elements, some of which have been adopted in later standards. Other user agents may not recognize non-standard elements, and they will be ignored, possibly causing the page to be displayed improperly.

In 1998, XML (a simplified form of SGML) introduced mechanisms to allow anyone to develop their own elements and incorporate them in XHTML documents, for use with XML-aware user agents.^[11]

Subsequently, HTML 4.01 was rewritten in an XML-compatible form, XHTML 1.0 (eXtensible HTML). The elements in each are identical, and in most cases valid XHTML 1.0 documents will be valid or nearly valid HTML 4.01 documents. This article mainly focuses on real HTML, unless noted otherwise; however, it remains applicable to XHTML. See HTML for a discussion of the minor differences between the two.

Element status[edit]

Since the first version of HTML, several elements have become outmoded, and are deprecated in later standards, or do not appear at all, in which case they are invalid (and will be found invalid, and perhaps not displayed, by validating user agents).^[12]

In HTML 4.01 / XHTML 1.0, the status of elements is complicated by the existence of three types of DTD:

• Transitional, which contain deprecated elements, but which were intended to provide a transitional period during which authors could update their practices;
• Frameset, which are versions of the Transitional DTDs which also allow authors to write frameset documents;
• Strict, which is the up-to-date (as at 1999) form of HTML.

HTML5 instead provides a listing of obsolete features to go along with the standardized normative content. They are broken down into “obsolete but conforming” for which implementation instructions exist and “non-conforming” ones that should be replaced.^[13]

The first Standard (HTML 2.0) contained four deprecated elements, one of which was invalid in HTML 3.2. All four are invalid in HTML 4.01 Transitional, which also deprecated a further ten elements. All of these, plus two others, are invalid in HTML 4.01 Strict. While the frame elements are still current in the sense of being present in the Transitional and Frameset DTDs, there are no plans to preserve them in future standards, as their function has been largely replaced, and they are highly problematic for user accessibility.

(Strictly speaking, the most recent XHTML standard, XHTML 1.1 (2001), does not include frames at all; it is approximately equivalent to XHTML 1.0 Strict, but also includes the Ruby markup module.)^[14]

A common source of confusion is the loose use of deprecated to refer to both deprecated and invalid status, and to elements which are expected to be formally deprecated in future.

Content vs. presentation and behavior[edit]

Since HTML 4, HTML has increasingly focused on the separation of content (the visible text and images) from presentation (like color, font size, and layout).^[15] This is often referred to as a separation of concerns. HTML is used to represent the structure or content of a document, its presentation remains the sole responsibility of CSS style sheets. A default style sheet is suggested as part of the CSS standard, giving a default rendering for HTML.^[16]

Behavior (interactivity) is also kept separate from content, and is handled by scripts. Images are contained in separate graphics files, separate from text, though they can also be considered part of the content of a page.

Separation of concerns allows the document to be presented by different user agents according to their purposes and abilities. For example, a user agent can select an appropriate style sheet to present a document by displaying on a monitor, printing on paper, or to determine speech characteristics in an audio-only user agent. The structural and semantic functions of the markup remain identical in each case.

Historically, user agents did not always support these features. In the 1990s, as a stop-gap, presentational elements (like <b> and <i>) were added to HTML, at the cost of creating problems for interoperability and user accessibility. This is now regarded as outmoded and has been superseded by style sheet-based design; most presentational elements are now deprecated.^[17]

External image files are incorporated with the <img /> or <object /> elements. (With XHTML, the SVG language can also be used to write graphics within the document, though linking to external SVG files is generally simpler.)^[18] Where an image is not purely decorative, HTML allows replacement content with similar semantic value to be provided for non-visual user agents.

An HTML document can also be extended through the use of scripts to provide additional behaviors beyond the abilities of HTML hyperlinks and forms.

The elements <style> and <script>, with related HTML attributes, provide style sheets and scripts.

• In the document head, <style /> and <script /> may link to shared external documents, or <style>...</style> and <script>...</script> may contain embedded instructions. (The <link> element can also be used to link style sheets.)
• <script /> or <script>...</script> can occur at any point in the document (head or body).
• The style attribute is valid in most document body elements (e.g. <div style="...">) for inclusion of inline style instructions.
• Event-handling attributes, which provide links to scripts, are optional in most elements.
• For user agents which do not operate scripts, the <noscript>...</noscript> element provides embedded alternative content where appropriate; however, it can only be used in the document head and in the body as a block-level element.

Document structure elements[edit]

<html>...</html>The root element of an HTML document; all other elements are contained in this.The HTML element delimits the beginning and the end of an HTML document.Both the start and end tags may be omitted (HTML5).^[6]Standardized in HTML 2.0; still current.

<head>...</head>Container for processing information and metadata for an HTML document.Both the start and end tags may be omitted and inferred from child elements (HTML5).^[6]Standardized in HTML 2.0; still current.(See document head elements for child elements.)

<body>...</body>Container for the displayable content of an HTML document.Both the start and end tags may be omitted and inferred from child elements (HTML5).^[6]Standardized in HTML 2.0; still current.(See document body elements for child elements.)

Document head elements[edit]

<base />Specifies a base URL for all relative href and other links in the document. Must appear before any element that refers to an external resource. HTML permits only one <base> element for each document. This element has HTML attributes, but no contents.A development version of this element (as BASE) is mentioned in HTML Tags; standardized in HTML 2.0; still current.

<basefont /> (deprecated)Specifies a base font size, typeface, and color for the document. Used together with <font> elements. Deprecated in favor of style sheets.Standardized in HTML 3.2; deprecated in HTML 4.0 Transitional; invalid in HTML 4.0 Strict.

<isindex /> (deprecated)<isindex> could either appear in the document head or in the body, but only once in a document. See Forms.

<link />Specifies links to other documents, such as previous and next links, or alternate versions.^[19] A common use is to link to external style sheets, using the form:<link rel="stylesheet" type="text/css" href="url" title="description_of_style">^[20]A less-common, but important, usage is to supply navigation hints consistently through use of microformats. Several common relationships are defined, that may be exposed to users through the browser interface rather than directly in the web page.<link rel="next" href="url">A document’s <head> element may contain any number of <link /> elements. This element has HTML attributes, but no contents.LINK existed in HTML Internet Draft 1.2, and was standardized in HTML 2.0; still current.

<meta />Main article: Meta elementCan be used to specify additional metadata about a document, such as its author, publication date, expiration date, language, page title, page description, keywords, or other information not provided through the other header elements and HTML attributes. Because of their generic nature, <meta /> elements specify associative key-value pairs. In general, a meta element conveys hidden information about the document. Several meta tags can be used, all of which should be nested in the head element. The specific purpose of each <meta /> element is defined by its attributes. Outside of XHTML, it is often given without the slash (<meta>), despite being a void element.In one form, <meta /> elements can specify HTTP headers which should be sent by a web server before the actual content. For example, <meta http-equiv="foo" content="bar" /> specifies that the page should be served with an HTTP header called foo that has a value bar.In the general form, a <meta /> element specifies name and associated contentHTML attributes describing aspects of the HTML page. To prevent possible ambiguity, an optional third attribute, scheme, may be supplied to specify a semantic framework that defines the meaning of the key and its value. For example, in <meta name="foo" content="bar" scheme="DC" /> the <meta /> element identifies itself as containing the foo element, with a value of bar, from the DC or Dublin Coreresource description framework.Standardized in HTML 2.0; still current.

<object>...</object>Used for including generic objects within the document header. Though rarely used within a <head> element, it could potentially be used to extract foreign data and associate it with the current document.Standardized in HTML 4.0; still current.

<script>...</script>Can act as a container for script instructions or link to an external script with the optional src attribute.^[21] Also usable in the document body to dynamically generate either both block or inline content.Standardized in HTML 3.2; still current.

<style>...</style>Specifies a style for the document, usually in the form:<style type="text/css"> ... </style>Can either act as a container for style instructions or link to external style sheets – for example, in CSS, with @import directives of the form:<style> @import url; </style>^[22]Standardized in HTML 3.2; still current.

<title>...</title>This tag defines a document title. Required in every HTML and XHTML document. User agents may use the title in different ways. For example:

• Web browsers usually display it in a window’s title bar when the window is open, and (where applicable) in the task bar when the window is minimized.
• It may become the default file-name when saving the page.
• We can use <title> element only one time in a web page, and when we make another page then we will use again another <title> element with new title (don’t take same name for all title tag in website, It can be problem for search engines).
• Web search engines‘ web crawlers may pay particular attention to the words used in the title.

The <title> element must not contain other elements, only text. Only one <title> element is permitted in a document.Existed in HTML Tags, and was standardized in HTML 2.0; still current.

Document body elements[edit]

In visual browsers, displayable elements can be rendered as either block or inline. While all elements are part of the document sequence, block elements appear within their parent elements:

• as rectangular objects which do not break across lines;
• with block margins, width and height properties which can be set independently of the surrounding elements.

Conversely, inline elements are treated as part of the flow of document text; they cannot have margins, width or height set, and do break across lines.

Block elements[edit]

Block elements, or block-level elements, have a rectangular structure. By default, these elements will span the entire width of its parent element, and will thus not allow any other element to occupy the same horizontal space as it is placed on.

The rectangular structure of a block element is often referred to as the box model, and is made up of several parts. Each element contains the following:

• The content of an element is the actual text (or other media) placed between the opening and closing tags of an element.
• The padding of an element is the space around the content but which still forms part of the element. Padding should not be used to create white space between two elements. Any background style assigned to the element, such as a background image or color, will be visible within the padding. Increasing the size of an element’s padding increases the amount of space this element will take up.
• The border of an element is the absolute end of an element, and spans the perimeter of that element. The thickness of a border increases the size of an element.
• The margin of an element is the white-space that surrounds an element. The content, padding and border of any other element will not be allowed to enter this area, unless forced to do so by some advanced CSS placement. Using most standard DTDs, margins on the left and right of different elements will push each other away. Margins on the top or bottom of an element, on the other hand, will not stack, or will intermingle. This means that the white-space between these elements will be as big as the larger margin between them.

The above section refers only to the detailed implementation of CSS rendering and has no relevance to HTML elements themselves.

Basic text[edit]

<p>...</p>Creates a paragraph, perhaps the most common block level element.P existed in HTML Tags, and was standardized in HTML 2.0; still current.

<h1>...</h1> <h2>...</h2> <h3>...</h3> <h4>...</h4> <h5>...</h5> <h6>...</h6>Section headings at different levels. h1 delimits the highest-level heading, h2 the next level down (sub-section), h3 for a level below that, and so on to h6. They are sometimes referred to collectively as hn tags, n meaning any of the available heading levels.Most visual browsers show headings as large bold text by default, though this can be overridden with CSS. Heading elements are not intended merely for creating large or bold text – in fact, they should not be used for explicitly styling text. Rather, they describe the document’s structure and organization. Some programs use them to generate outlines and tables of contents.Headings existed in HTML Tags, and were standardized in HTML 2.0; still current.

Lists[edit]

<dl>...</dl>“Definition list” redirects here. For Wikipedia’s article on lists of definitions, see Glossary.A description list (a.k.a. association list or definition list), which consists of name–value groups,^[23] and was known as a definition list prior to HTML5.^[24] Description lists are intended for groups of “terms and definitions, metadata topics and values, questions and answers, or any other groups of name–value data”.^[25]DL existed in HTML Tags, and was standardized in HTML 2.0; still current.

<dt>...</dt>A name in a description list (previously definition term in a definition list).DT existed in HTML Tags, and was standardized in HTML 2.0; still current.

<dd>...</dd>A value in a description list (previously definition data in a definition list).DD existed in HTML Tags, and was standardized in HTML 2.0; still current.

<ol>...</ol>An ordered (enumerated) list. The type attribute can be used to specify the kind of marker to use in the list, but style sheets give more control. The default is Arabic numbering. In an HTML attribute: <ol type="foo">; or in a CSS declaration: ol { list-style-type: foo; } – replacing foo with one of the following:

Style	HTML value	CSS value
A, B, C …	A	upper-alpha
a, b, c …	a	lower-alpha
I, II, III …	I	upper-roman
i, ii, iii …	i	lower-roman
1, 2, 3 …	1	decimal

CSS provides several other options not available as pure-HTML markup, including none, and options for CJK, Hebrew, Georgian, and Armenian script.OL existed in HTML Internet Draft 1.2, and was standardized in HTML 2.0; still current.

<ul>...</ul>An unordered (bulleted) list. The type of list item marker can be specified in an HTML attribute: <ul type="foo">; or in a CSS declaration: ul { list-style-type: foo; } – replacing foo with one of the following (the same values are used in HTML and CSS): disc (the default), square, or circle. Only the CSS method is supported in HTML5. CSS also provides none, and the ability to replace these bullets with custom images.UL existed in HTML Tags, and was standardized in HTML 2.0; still current.

<li>...</li>A list item in ordered (ol) or unordered (ul) lists.LI existed in HTML Tags, and was standardized in HTML 2.0; still current.

<dir>...</dir> (deprecated)A directory listing. The original purpose of this element was never widely supported; deprecated in favor of <ul>.DIR existed in HTML Tags, and was standardized in HTML 2.0; deprecated in HTML 4.0 Transitional; invalid in HTML 4.0 Strict.

Other block elements[edit]

<address>...</address>Contact information for the document author.ADDRESS existed in HTML Tags, and was standardized in HTML 2.0; still current.

<article>...</article>Main article: Article elementUsed for articles and other similar content.Standardized in HTML5.

<aside>...</aside>Used for content in a document which is separate from the main page content, for example, sidebars or advertising.Standardized in HTML5.

<blockquote>...</blockquote>Main article: Blockquote elementA block level quotation, for when the quotation includes block level elements, e.g. paragraphs. The cite attribute (not to be confused with the <cite> element) may give the source, and must be a fully qualified Uniform Resource Identifier.The default presentation of block quotations in visual browsers is usually to indent them from both margins. This has led to the element being unnecessarily used just to indent paragraphs, regardless of semantics. For quotations not containing block level elements see the quote (<q>) element.BLOCKQUOTE existed in HTML Internet Draft 1.2, and was standardized in HTML 2.0; still current. See blockquote element for more information.

<center>...</center> (deprecated)Creates a block-level center-aligned division. Deprecated in favor of <div> or another element with centering defined using style sheets.Standardized in HTML 3.2; deprecated in HTML 4.0; not supported in HTML5.

<del>...</del>Marks a deleted section of content. This element can also be used as inline.Standardized in HTML 4.0; still current.

<div>...</div>Main article: Span and divA block-level logical division. A generic element with no semantic meaning used to distinguish a document section, usually for purposes such as presentation or behavior controlled by style sheets or DOM calls.Proposed in the HTML 3.0 Drafts; Standardized in HTML 3.2; still current.

<figure>...</figure>Used to group images and captions, along with <figcaption>.Standardized in HTML5.

<figcaption>...</figcaption>A caption for an image. Always placed inside the <figure> element.Standardized in HTML5.

<footer>...</footer>Used for document footers. These might contain author or copyright information, or links to other pages.Standardized in HTML5.

<header>...</header>Used for document headers. These typically contain content introducing the page.Standardized in HTML5.

<hr />A thematic break (originally: horizontal rule). Presentational rules can be drawn with style sheets.Standardized in HTML 2.0; still current.

<ins>...</ins>Marks a section of inserted content. This element can also be used as inline.Standardized in HTML 4.0; still current.

<main>...</main>Contains the main content of a document.Standardized in HTML 5.1.

<menu>...</menu> (deprecated)HTML 2.0: A menu listing. Should be more compact than a <ul> list.MENU existed in HTML Tags, and was standardized in HTML 2.0; deprecated in HTML 4.0 Transitional; invalid in HTML 4.0 Strict; then redefined in HTML5, but removed in HTML 5.2.

<nav>...</nav>Used in navigational sections of articles (areas of webpages which contain links to other webpages).Standardized in HTML5.

<noscript>...</noscript>Replacement content for scripts. Unlike script this can only be used as a block-level element.Standardized in HTML 4.0; still current.

<pre>...</pre>Pre-formatted text. Text within this element is typically displayed in a non-proportional font exactly as it is laid out in the file (see ASCII art). Whereas browsers ignore white-space for other HTML elements, in <pre>...</pre>, white-space should be rendered as authored. (With the CSS properties: { white-space: pre; font-family: monospace; }, other elements can be presented in the same way.) This element can contain any inline element except: <image>, <object>, <big>, <small>, <sup>, and <sub>...</sub>.PRE existed in HTML Internet Draft 1.2, and was standardized in HTML 2.0; still current.

<section>...</section>Used for generic sections of a document. This is different from <div> in that it is only used to contain sections of a page, which the W3C defines as a group of content with a similar theme.Standardized in HTML5.

<script>...</script>Places a script in the document. Also usable in the head and in inline contexts. It may be used as <script /> with a src attribute to supply a URL from which to load the script, or used as <script>...</script> around embedded script content.Note:<script> is not itself either a block or inline element; by itself it should not display at all, but it can contain instructions to dynamically generate either both block or inline content.Standardized in HTML 3.2; still current.

Inline elements[edit]

Inline elements cannot be placed directly inside the <body> element; they must be wholly nested within block-level elements.^[26]

Anchor[edit]

<a>...</a>An anchor element is called an anchor because web designers can use it to “anchor” a URL to some text on a web page. When users view the web page in a browser, they can click the text to activate the link and visit the page whose URL is in the link.^[27]In HTML, an anchor can be either the origin (the anchor text) or the target (destination) end of a hyperlink.With the attribute href,^[28] the anchor becomes a hyperlink to either another part of the document or another resource (e.g. a webpage) using an external URL. Alternatively (and sometimes concurrently), with the name or idHTML attributes set, the element becomes a link target. A Uniform Resource Locator (URL) can link to this target via a fragment identifier, commonly referred to as a “# link”. In HTML5, any element can now be made into a target by using the id attribute,^[29] so using <a name="foo">...</a> is not necessary, although this way of adding anchors continues to work.To illustrate: the header of a table of contents section on example.com’s homepage could be turned into a target by writing<h2><a name="contents">Table of contents</a></h2>Continuing with this example, now that the section has been marked up as a target, it can be referred to from external sites with a link like<a href="http://example.com#contents">see contents</a>or with a link on the same page like:<a href="#contents">contents, above</a>The attribute title may be set to give brief information about the link:<a href="URL" title="additional information">link text</a>In most graphical browsers, when the cursor hovers over a link, the cursor changes into a hand with an extended index finger and the title value is displayed in a tooltip or in some other manner. Some browsers render alt text the same way, although this is not what the specification calls for.A existed in HTML Tags, and was standardized in HTML 2.0; still current

Phrase elements[edit]

This section may be confusing or unclear to readers. In particular, the section lacks a definition, gloss, or explanation of the term of art ‘phrase element‘. Why are these particular elements grouped together? Why is ‘Phrase elements’ the name of this section? It all seems arbitrary. Please help us clarify the section. There might be a discussion about this on the talk page. (October 2018) (Learn how and when to remove this template message)

General[edit]

<abbr>...</abbr>Marks an abbreviation, and can make the full form available:<abbr title="abbreviation">abbr.</abbr>Standardized in HTML 4.0; still current.

<acronym>...</acronym> (deprecated)Similar to the <abbr> element, but marks an acronym:<acronym title="Hyper-Text Mark-up Language">HTML</acronym>Standardized in HTML 4.0; still current, not supported in HTML5. Recommended replacement is the abbr tag.^[30]

<dfn>...</dfn>inline definition of a single term.DFN existed in HTML Internet Draft 1.2, and was fully standardized in HTML 3.2; still current.

<em>...</em>Emphasis (conventionally displayed in italics)EM existed in HTML Internet Draft 1.2, and was standardized in HTML 2.0; still current.

<strong>...</strong>importance; originally strong emphasis (conventionally displayed bold).An aural user agent may use different voices for emphasis.STRONG existed in HTML Internet Draft 1.2, and was standardized in HTML 2.0; still current, redefined in HTML5.

Computer phrase elements[edit]

These elements are useful primarily for documenting computer code development and user interaction through differentiation of source code (<code>), variables (<var>), user input (<kbd>), and terminal or other output (<samp>).

<code>...</code>A code snippet (code example). Conventionally rendered in a mono-space font.CODE existed in HTML Internet Draft 1.2, and was standardized in HTML 2.0; still current.

<kbd>...</kbd>Keyboard – text to be entered by the user (kbd example).KBD existed in HTML Internet Draft 1.2, and was standardized in HTML 2.0; still current.

<samp>...</samp>Sample output – from a program or script: (samp example).SAMP existed in HTML Internet Draft 1.2, and was standardized in HTML 2.0; still current.

<var>...</var>Variable (var example).VAR existed in HTML Internet Draft 1.2, and was standardized in HTML 2.0; still current.

Presentation[edit]

As visual presentational markup only applies directly to visual browsers, its use is discouraged. Style sheets should be used instead. Several of these elements are deprecated or invalid in HTML 4 / XHTML 1.0, and the remainder are invalid in the current draft of XHTML 2.0. The current draft of HTML5, however, re-includes <s>, <u>, and <small>, assigning new semantic meaning to each. In an HTML5 document, the use of these elements is no longer discouraged, provided that it is semantically correct.

<b>...</b>In HTML 4, set font to boldface where possible. Equivalent CSS: { font-weight: bold; }. The <b> element usually has the same effect in visual browsers, as well as having more semantic meaning, under HTML 4.01.In HTML5, however, <b> has its own meaning, distinct from that of <strong>. It denotes “text to which attention is being drawn for utilitarian purposes without conveying any extra importance and with no implication of an alternate voice or mood.”^[31]B existed in HTML Internet Draft 1.2, and was standardized in HTML 2.0; still current, redefined in HTML5.

<i>...</i>In HTML 4, set font to italic where possible. Equivalent CSS: { font-style: italic; }. Using <em>...</em> has the same visual effect in most browsers, as well as having a semantic meaning as emphasis, under HTML 4.01. (Purely typographic italics have many non-emphasis purposes, as HTML 5 more explicitly recognized.)In HTML5, however, <i> has its own semantic meaning, distinct from that of <em>. It denotes “a different quality of text” or “an alternative voice or mood “e.g., a thought, a ship name, a binary species name, a foreign-language phrase, etc.”^[32]I existed in HTML Internet Draft 1.2, and was standardized in HTML 2.0; still current, redefined in HTML5.

<u>...</u>In HTML 4, underlined text. Equivalent CSS: { text-decoration: underline; }. Deprecated in HTML 4.01. Restored in HTML5.In HTML5, the <u> element denotes “a span of text with an unarticulated, though explicitly rendered, non-textual annotation, such as labelling the text as being a proper name in Chinese text (a Chinese proper name mark), or labelling the text as being misspelt.” The HTML5 specification reminds developers that other elements are almost always more appropriate than <u> and admonishes designers not to use underlined text where it could be confused for a hyper-link.^[33]U existed in HTML Internet Draft 1.2, was standardized in HTML 3.2 but was deprecated in HTML 4.0 Transitional and was invalid in HTML 4.0 Strict. Reintroduced in HTML5.

<small>...</small>In HTML 4, decreased font size (smaller text). Equivalent CSS: { font-size: smaller; }In HTML5, the <small> element denotes “side comments such as small print.”^[34] This has caused some confusion with the <aside>...</aside> element.Standardized in HTML 3.2; still current.

<s>...</s>In HTML 4, indicated strike-through text (Strikethrough) and was equivalent to <strike>.In HTML5, the <s> element denotes information that is “no longer accurate or no longer relevant”, and is not to be confused with <del>, which indicates removal/deletion.^[35]S was deprecated in HTML 4.0 Transitional (having not appeared in any previous standard), and was invalid in HTML 4.0 Strict. Reintroduced in HTML5, which instead deprecated <strike>.

<big>...</big> (deprecated)Increased font size (bigger text). Equivalent CSS: { font-size: larger; }Standardized in HTML 3.2; not supported in HTML5.

<strike>...</strike> (deprecated)Strike-through text (Strikethrough), (Equivalent CSS: { text-decoration: line-through; })STRIKE was standardized in HTML 3.2; deprecated in HTML 4.0 Transitional; invalid in HTML 4.0 Strict.

<tt>...</tt> (deprecated)Fixed-width font (typewriter-like), also known as teletype, thus “tt”. (Equivalent CSS: { font-family: monospace; })TT existed in HTML Internet Draft 1.2, and was Standardized in HTML 2.0; not supported^[36] in HTML5. Possible replacements: <kbd> for marking user input, <var> for variables (usually rendered italic, and not with a change to monospace), <code> for source code, <samp> for output.^[36]

<font>...</font> (deprecated)<font [color=<var>color</var>] [size=<var>size</var>] [face=<var>face</var>]>...</font>Can specify the font color with the color attribute (note the American spelling), typeface with the face attribute, and absolute or relative size with the size attribute.Examples (all uses are deprecated, use CSS equivalents if possible):

1. <font color="green">text</font> creates green text.
2. <font color="#114499">text</font> creates text with hexadecimal color #114499.
3. <font size="4">text</font> creates text with size 4. Sizes are from 1 to 7. The standard size is 3, unless otherwise specified in the <body> or other tags.
4. <font size="+1">text</font> creates text with size 1 bigger than the standard. <font size="-1">text</font> is opposite.
5. <font face="Courier">text</font> makes text with Courier font.

Equivalent CSS for font attributes:

• <font size="N"> corresponds to {font-size: Yunits} (the HTML specification does not define the relationship between size N and unit-size Y, nor does it define a unit).
• <font color="red"> corresponds to { color: red; }
• <font face="Times New Roman"> corresponds to { font-family: 'Times New Roman', Times, serif; } – CSS supports a font stack, of two or more alternative fonts.

Standardized in HTML 3.2; deprecated in HTML 4.0 Transitional; invalid in HTML 4.0 Strict. Not part of HTML5.

Span[edit]

<span>...</span>Main article: Span and divAn inline logical division. A generic element with no semantic meaning used to distinguish a document section, usually for purposes such as presentation or behavior controlled by style sheets or DOM calls.Standardized in HTML 4.0; still current.

Other inline elements[edit]

<br />A forced line break.Standardized in HTML 2.0; still current.

<bdi>...</bdi>Isolates an inline section of text that may be formatted in a different direction from other text outside of it, such as user-generated content with unknown directionality.Standardized in HTML5.

<bdo>...</bdo>Marks an inline section of text in which the reading direction is the opposite from that of the parent element.Standardized in HTML 4.0; still current.

<cite>...</cite>A citation or a reference for a quote or statement in the document.CITE existed in HTML Internet Draft 1.2, and was standardized in HTML 2.0; still current.Note: The HTML 5 specifications have been confusingly forked,^[37] including with regard to this element. In HTML 4 and earlier, <cite> was for “a citation or a reference to other sources” without any particular limitations or requirements.^[38] The W3C HTML 5 spec uses a refinement of this idea, reflecting how the element has historically been used, but now requiring that it contain (but not be limited to) at least one of “the title of the work or the name of the author (person, people or organization) or an URL reference, or a reference in abbreviated form as per the conventions used for the addition of citation metadata.”^[39] But the WHATWG spec only permits the element to be used around the title of a work.^[40] The W3C specs began with the broader definition, then switched to the very narrow one after WHATWG made this change. However, W3C reverted their own change in 2012, in response to negative developer-community feedback; the element was in broadly-deployed use with the broader scope, e.g., various blog and forum platforms wrap commenters’ IDs and e-mail addresses in <cite>...</cite>, and people using the element for bibliographic citations were (and still are) routinely wrapping each entire citation in this element.Another problem with the element is that WHATWG recommends that it be italicized by default (thus almost all browsers do so), because it (in their view) is only for publication titles. By convention, however, only certain kinds of titles actually take italics, while others are expected to be put in quotation marks, and standards may actually vary by publishing context and language. Consequently, many website authors and admins use a site-wide stylesheet to undo this element’s auto-italics.

<data>...</data>Links inline content with a machine-readable translation.Standardized in HTML5.^[41]

<del>...</del>Deleted text. Typically rendered as a strikethrough: Deleted text.Standardized in HTML 4.0; still current.

<ins>...</ins>Inserted text. Often used to mark up replacement text for material struck with <del> or <s>. Typically rendered underlined: Inserted text.Standardized in HTML 4.0; still current.Both <ins> and elements may also be used as block elements: containing other block and inline elements. However, these elements must still remain wholly within their parent element to maintain a well-formed HTML document. For example, deleting text from the middle of one paragraph across several other paragraphs and ending in a final paragraph would need to use three separate elements. Two elements would be required as inline elements to indicate the deletion of text in the first and last paragraphs, and a third, used as a block element, to indicate the deletion in the intervening paragraphs.

<mark>...</mark>Produces text that looks like this. Intended for highlighting relevant text in a quotation.Standardized in HTML5.

<q>...</q>An inline quotation (for block level quotation see <blockquote>). Quote elements may be nested.<q>should automatically generate quotation marks in conjunction with style sheets. Practical concerns due to browser non-compliance may force authors to find workarounds.The cite attribute gives the source, and must be a fully qualified URI.Standardized in HTML 4.0; still current.Note: Lengthy inline quotations may be displayed as indented blocks (as block-quote) using style sheets. For example, with a suitable CSS rule associated with q.lengthy: <q>Lengthy quote here.</q >

<rb>...</rb>Represents the base component of a ruby annotation.Standardized in HTML5.^[42]

<rp>...</rp>Provides fallback parenthesis for browsers lacking ruby annotation support.Standardized in HTML5.^[43]

<rt>...</rt>Indicates pronunciation for a character in a ruby annotation.Standardized in HTML5.^[44]

<rtc>...</rtc>Semantic annotations for a ruby annotation.Standardized in HTML5.^[45]

<ruby>...</ruby>Represents a ruby annotation for showing the pronunciation of East Asian characters.Standardized in HTML5.^[46]

<script>...</script>Places a script in the document. Also usable in the head and in block contexts.Note:<script> is not itself either a block or inline element; by itself it should not display at all, but it can contain instructions to dynamically generate either both block or inline content.Standardized in HTML 3.2; still current.

<sub>...</sub> and <sup>...</sup>Mark _subscript or ^superscript text. (Equivalent CSS: { vertical-align: sub; } and { vertical-align: super; }, respectively.)Both were proposed in the HTML 3.0 Drafts; Standardized in HTML 3.2; still current.

<template>...</template>Code fragments to be copied by scripts.Standardized in HTML5.

<time>...</time>Represents a time on the 24-hour clock or a date on the Gregorian calendar, optionally with time and timezone information. Also allows times and dates to be represented in a machine-readable format.Standardized in HTML5.^[47]

<wbr />An optional word break.Was widely used (and supported by all major browsers) for years despite being non-standard until finally being standardized in HTML5.

Images and objects[edit]

<applet>...</applet> (deprecated)Embeds a Java applet in the page. Deprecated in favor of <object>, as it could only be used with Java applets, and had accessibility limitations.Standardized in HTML 3.2; deprecated in HTML 4.0 Transitional; invalid in HTML 4.0 Strict. As of 2011, still widely used as the implementations of the replacing <object> are not consistent between different browsers.

<area />Specifies a focusable area in a <map>.Standardized in HTML 3.2; still current.

<audio>...</audio>Adds playable HTML5 audio to the page. The audio URL is determined using the src attribute. Supported audio formats vary from browser to browser.Standardized in HTML5.

<canvas>...</canvas>Main article: Canvas elementAdds a canvas whose contents can be edited with JavaScript. Frequently used for online games.Standardized in HTML5.

<embed>...</embed>Inserts a non-standard object (like applet) or external content (typically non-HTML) into the document. Deprecated in HTML 4 in favor of <object>, but then was added back into the HTML5 specification^[48][49]

<img />Used by visual user agents to insert an image in the document. The src attribute specifies the image URL. The required alt attribute provides alternative text in case the image cannot be displayed.^[50] (Though alt is intended as alternative text, Microsoft Internet Explorer 7 and below render it as a tooltip if no title attribute is given.^[51]Safari and Google Chrome, on the other hand, do not display the alt attribute at all.)^[52] The <img /> element was first proposed by Marc Andreessen and implemented in the NSCA Mosaic web browser.^[53]IMG existed in HTML Internet Draft 1.2, and was standardized in HTML 2.0; still current.

<map>...</map>Specifies a client-side image map.Standardized in HTML 3.2; still current.

<object>...</object>Includes an object in the page of the type specified by the type attribute. This may be in any MIME-type the user agent understands, such as an embedded HTML page, a file to be handled by a plug-in such as Flash, a Javaapplet, a sound file, etc.Standardized in HTML 4.0; still current.

<param />Originally introduced with <applet>, this element is now used with <object>, and should only occur as a child of <object>. It uses HTML attributes to set a parameter for the object, e.g. width, height, font, background color, etc., depending on the type of object. An object can have multiple <param /> elements.Standardized in HTML 3.2; still current.

<source>...</source>Specifies different sources for audio or video. Makes use of the src attribute in a way similar to the <video> and <audio> elements.Standardized in HTML5.

<track>...</track>Provides text tracks, like subtitles and captions, for audio and video.Standardized in HTML5.

<video>...</video>Adds a playable HTML5 video to the page. The video URL is determined using the src attribute. Supported video formats vary from browser to browser.Standardized in HTML5.

Forms[edit]

Main article: Form (HTML)

These elements can be combined into a form or in some instances used separately as user-interface controls; in the document, they can be simple HTML or used in conjunction with Scripts. HTML markup specifies the elements that make up a form, and the method by which it will be submitted. However, some form of scripts (server-side, client-side, or both) must be used to process the user’s input once it is submitted.

(These elements are either block or inline elements, but are collected here as their use is more restricted than other inline or block elements.)

<form action="url">...</form>Creates a form. The <form> element specifies and operates the overall action of a form area, using the required action attribute.Standardized in HTML 2.0; still current.

<button>...</button>A generic form button which can contain a range of other elements to create complex buttons.Standardized in HTML 4.0; still current.

<datalist>...</datalist>A list of options for use in form elements.Standardized in HTML5.

<fieldset>...</fieldset>A container for adding structure to forms. For example, a series of related controls can be grouped within a <fieldset>, which can then have a <legend> added in order to identify their function.Standardized in HTML 4.0; still current.

<input /><input> elements allow a variety of standard form controls to be implemented.Standardized in HTML 2.0; still current.Input Types: type=”checkbox”A checkbox. Can be checked or unchecked. type=”radio”A radio button. If multiple radio buttons are given the same name, the user will only be able to select one of them from this group. type=”button”A general-purpose button. The element <button> is preferred if possible (i.e., if the client supports it) as it provides richer possibilities. type=”submit”A submit button. type=”image”An image button. The image URL may be specified with the src attribute. type=”reset”A reset button for resetting the form to default values. type=”text”A one-line text input field. The size attribute specifies the default width of the input in character-widths. max-length sets the maximum number of characters the user can enter (which may be greater than size). type=”search”A variation of text which produces a search bar. type=”password”A variation of text. The difference is that text typed in this field is masked – characters are displayed as an asterisk, a dot, or another replacement. The password is still submitted to the server as plaintext, so an underlying secure communication protocol like HTTPS is needed if confidentiality is a concern. type=”file”A file select field (for uploading files to a server). type=”tel”A variation of text for telephone numbers. type=”email”A variation of text for email addresses. type=”url”A variation of text for URLs. type=”date”A date selector. type=”time”A time selector. type=”number”A variation of text for numbers. type=”range”Produces a slider for that returns a number, but the number is not visible to the user. type=”color”A color picker. type=”hidden”hidden inputs are not visible in the rendered page, but allow a designer to maintain a copy of data that needs to be submitted to the server as part of the form. This may, for example, be data that this web user entered or selected on a previous form that needs to be processed in conjunction with the current form. Not displayed to the user but data can still be altered client-side by editing the HTML source.

<isindex /> (deprecated)<isindex /> could either appear in the document head or in the body, but only once in a document.<isindex /> operated as a primitive HTML search form; but was de facto obsoleted by more advanced HTML forms introduced in the early to mid-1990s. Represents a set of hyperlinks composed of a base URI, an ampersand and percent-encoded keywords separated by plus signs.ISINDEX existed in HTML Tags; standardized in HTML 2.0; deprecated in HTML 4.0 Transitional; invalid in HTML 4.0 Strict.

<keygen>...</keygen> (deprecated)A key pair generator.Standardized in HTML5, but removed in HTML 5.2.

<label for="id">...</label>Creates a label for a form input, such as radio. Clicking on the label fires a click on the matching input.Standardized in HTML 4.0; still current.

<legend>...</legend>A legend (caption) for a <fieldset>.Standardized in HTML 4.0; still current.

<meter>...</meter>A meter which needs a value attribute. Can also have: min, low, high, and max.Standardized in HTML5.

<option value="x">...</option>Creates an item in a <select> list.Standardized in HTML 2.0; still current.

<optgroup>...</optgroup>Identifies a group of <option> elements in a <select> list.Standardized in HTML 4.0; still current.

<output>...</output>The value of a form element.Standardized in HTML5.

<progress>...</progress>A bar for showing the progress of an action.Standardized in HTML5.

<select name="xyz">...</select>Creates a selection list, from which the user can select a single option. May be rendered as a dropdown list.Standardized in HTML 2.0; still current.

<textarea rows="8">...</textarea>A multiple-line text area, the size of which is specified by cols (where a column is a one-character width of text) and rowsHTML attributes. The content of this element is restricted to plain text, which appears in the text area as default text when the page is loaded.Standardized in HTML 2.0; still current.

Tables[edit]

The format of HTML Tables was proposed in the HTML 3.0 Drafts and the later RFC 1942 HTML Tables. They were inspired by the CALS Table Model. Some elements in these proposals were included in HTML 3.2; the present form of HTML Tables was standardized in HTML 4. (Many of the elements used within tables are neither block nor inline elements.)

<table>...</table>Identifies a table. Several HTML attributes are possible in HTML Transitional, but most of these are invalid in HTML Strict and can be replaced with style sheets. The summary attribute is informally required for accessibility purposes, though its usage is not simple.Proposed in the HTML 3.0 Drafts; Standardized in HTML 3.2; still current.

<tr>...</tr>Contains a row of cells in a <table>.Proposed in the HTML 3.0 Drafts; Standardized in HTML 3.2; still current.

<th>...</th>A <table> header cell; contents are conventionally displayed bold and centered. An aural user agent may use a louder voice for these items.Proposed in the HTML 3.0 Drafts; Standardized in HTML 3.2; still current.

<td>...</td>A <table> data cell.Proposed in the HTML 3.0 Drafts; Standardized in HTML 3.2; still current.

<colgroup>...</colgroup>Specifies a column group in a <table>.Proposed in HTML Tables; Standardized in HTML 4.0; still current.

<col>...</col>Specifies a column in a <table>.Proposed in HTML Tables; Standardized in HTML 4.0; still current.

<caption>...</caption>Specifies a caption for a <table>.Proposed in the HTML 3.0 Drafts; Standardized in HTML 3.2; still current.

<thead>...</thead>Specifies the header part of a <table>. This section may be repeated by the user agent if the table is split across pages (in printing or other paged media).Proposed in HTML Tables; Standardized in HTML 4.0; still current.

<tbody>...</tbody>Specifies a body of data for a <table>.Proposed in HTML Tables; Standardized in HTML 4.0; still current.

<tfoot>...</tfoot>Specifies the footer part of a <table>. Like <thead>, this section may be repeated by the user agent if the table is split across pages (in printing or other paged media).Proposed in HTML Tables; Standardized in HTML 4.0; still current.

Frames[edit]

Main article: Framing (World Wide Web)

Frames allow a visual HTML Browser window to be split into segments, each of which can show a different document. This can lower bandwidth use, as repeating parts of a layout can be used in one frame, while variable content is displayed in another. This may come at a certain usability cost, especially in non-visual user agents,^[54] due to separate and independent documents (or websites) being displayed adjacent to each other and being allowed to interact with the same parent window. Because of this cost, frames (excluding the <iframe> element) are only allowed in HTML 4.01 Frame-set. Iframes can also hold documents on different servers. In this case the interaction between windows is blocked by the browser. Sites like Facebook and Twitter use iframes to display content (plugins) on third party websites. Google AdSense uses iframes to display banners on third party websites.

In HTML 4.01, a document may contain a <head> and a <body> or a <head> and a <frameset>, but not both a <body> and a <frameset>. However, <iframe> can be used in a normal document body.

<frameset>...</frameset> (deprecated)Contains the set of <frame /> elements for a document. The layout of frames is given by comma separated lists in the rows and colsHTML attributes.Standardized in HTML 4.0 Frameset, obsolete in HTML5.

<frame /> (deprecated)Defines a single frame, or region, within the <frameset>. A separate document is linked to a frame using the src attribute inside the <frame /> element.Standardized in HTML 4.0 Frameset, obsolete in HTML5.

<noframes>...</noframes> (deprecated)Contains normal HTML content for user agents that don’t support <frame /> elements.Standardized in HTML 4.0 Transitional, obsolete in HTML5.

<iframe>...</iframe>An inline frame places another HTML document in a frame. Unlike an <object /> element, an <iframe> can be the “target” frame for links defined by other elements, and it can be selected by the user agent as the focus for printing, viewing its source, and so on.The content of the element is used as alternative text to be displayed if the browser does not support inline frames.First introduced by Microsoft Internet Explorer in 1997, standardized in HTML 4.0 Transitional, allowed in HTML5.

longdesc attribute[edit]

In HTML, longdesc is an attribute used within the <img />, <frame />, or <iframe> elements. It is supposed to be a URL^{[note 8]} to a document that provides a long description for the image, frame, or iframe in question.^[55] Note that this attribute should contain a URL, not – as is commonly mistaken – the text of the description itself.

longdesc was designed to be used by screen readers to display image information for computer users with accessibility issues, such as the blind or visually impaired, and is widely implemented by both web browsers and screen readers.^[56] Some developers object that^[57] it is actually seldom used for this purpose because there are relatively few authors who use the attribute and most of those authors use it incorrectly; thus, they recommend deprecating longdesc.^[58] The publishing industry has responded, advocating the retention of longdesc.^[59]

Example[edit]

<img src="Hello.jpg" longdesc="description.html">

Content of description.html:

<br />
<p>This is an image of a two-layered birthday cake.</p>
...

Linking to the long description in the text[edit]

Since very few graphical browsers support making the link available natively (Opera and iCab being the exceptions), it is useful to include a link to the description page near the <img /> element whenever possible, as this can also aid sighted users.

Example[edit]

<img src="Hello.jpg" longdesc="description.html" /> [<a href=
"description.html" title="long description of the image">D</a>]

Historic elements[edit]

Main article: Comparison of layout engines (Non-standard HTML)

The following elements were part of the early HTML developed by Tim Berners-Lee from 1989–91; they are mentioned in HTML Tags, but deprecated in HTML 2.0 and were never part of HTML standards.

<listing>...</listing> (deprecated)This element displayed the text inside the tags in a monospace font and without interpreting the HTML. The HTML 2.0 specification recommended rendering the element at up to 132 characters per line.Deprecated in HTML 3.2; obsolete in HTML5.^[60]

<plaintext /> (deprecated)<plaintext /> does not have an end tag as it terminates the markup and causes the rest of the document to be parsed as if it were plaintext.<plaintext /> existed in HTML Tags; deprecated in HTML 2.0; invalid in HTML 4.0.

<xmp>...</xmp> (deprecated)This element displayed the text inside the tags in a monospace font and without interpreting the HTML. The HTML 2.0 specification recommended rendering the element at 80 characters per line.Deprecated in HTML 3.2; obsolete in HTML5.^[61]

<nextid /> (deprecated)This element enabled NeXT web designing tool to generate automatic NAME labels for its anchors and was itself automatically generated.^[62]<nextid /> existed in HTML Tags (described as obsolete); deprecated in HTML 2.0; invalid in HTML 3.2 and later.

Non-standard elements[edit]

Main article: Comparison of layout engines (Non-standard HTML)

This section lists some widely used obsolete elements, which means they are not used in valid code. They may not be supported in all user agents.

<blink>...</blink> (deprecated)Main article: Blink elementCauses text to blink. Introduced in imitation of the ANSI escape codes. Can be done with CSS where supported: {text-decoration: blink} (This effect may have negative consequences for people with photosensitive epilepsy;^[63] its use on the public Internet should follow the appropriate guidelines.)<blink> originated in Netscape Navigator and is mostly recognized by its descendants, including Firefox; deprecated or invalid in HTML 2.0 and later. Note that the replacement CSS tag, while standard, is not required to be supported.

<layer>...</layer> (deprecated)Main article: Layer elementCreates an absolute positioned and framed layer. Can be done with frames and/or CSS instead. There are attributes, including ID, LEFT, TOP, PAGEX, PAGEY, SRC, Z-INDEX, ABOVE, WIDTH, HEIGHT, BELOW, CLIP, VISIBILITY and CLIP.<layer> originated in Netscape 4; deprecated or invalid in HTML 4.01 and later.

<marquee>...</marquee> (deprecated)Main article: Marquee elementCreates scrolling text. Can be done with scripting instead. (This effect may have negative consequences for people with photosensitive epilepsy;^[63] its use on the public Internet should follow the appropriate guidelines.) There are three options, including Alternate, Scroll and slide. Scrolldelay can also be added.<marquee> originated in Microsoft Internet Explorer; deprecated or invalid in HTML 4.01 and later.

<nobr>...</nobr> (deprecated)Causes text to not break at end of line, preventing word wrap where text exceeds the width of the enclosing object. Adjacent text may break before and after it. Can be done with CSS: {white-space: nowrap;}<nobr> is a proprietary element which is recognized by most browsers for compatibility reasons; deprecated or invalid in HTML 2.0 and later.

<noembed>...</noembed> (deprecated)Specifies alternative content, if the embed cannot be rendered. Replaced by the content of the <embed> or <object> element.