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Saturday, 27 June 2015

Programing laguage HTML

HTML


 Hyper Text Markup Language, commonly referred to as HTML, is the standard markup language used to create web pages.[1] It is written in the form of HTML elements consisting of tags enclosed in angle brackets (like<html>). HTML tags most commonly come in pairs like <h1> and </h1>, although some represent empty elements and so are unpaired, for example<img>. The first tag in such a pair is the start tag, and the second is the end tag (they are also called opening tags and closing tags).
Web browsers can read HTML files and render them into visible or audible web pages. Browsers do not display the HTML tags and scripts, but use them to interpret the content of the page. HTML describes the structure of a websitesemantically along with cues for presentation, making it a markup language, rather than a programming language.
HTML elements form the building blocks of all websites. HTML allows images and objects to be embedded and can be used to create interactive forms. It provides a means to create structured documents by denoting structural semantics for text such as headings, paragraphs, lists, links, quotes and other items. It can embed scripts written in languages such as JavaScript which affect the behavior of HTML web pages.
Web browsers can also refer to Cascading Style Sheets (CSS) to define the look and layout of text and other material. The World Wide Web Consortium(W3C), maintainer of both the HTML and the CSS standards, has encouraged the use of CSS over explicit presentational HTML since 1999.[2]

Contents

  • 1 History
    • 1.1 Development
    • 1.2 HTML versions timeline
      • 1.2.1 HTML draft version timeline
      • 1.2.2 XHTML versions
  • 2 Markup
    • 2.1 Elements
      • 2.1.1 Element examples
      • 2.1.2 Attributes
    • 2.2 Character and entity references
    • 2.3 Data types
    • 2.4 Document type declaration
  • 3 Semantic HTML
  • 4 Delivery
    • 4.1 HTTP
    • 4.2 HTML e-mail
    • 4.3 Naming conventions
    • 4.4 HTML Application
  • 5 HTML4 variations
    • 5.1 SGML-based versus XML-based HTML
    • 5.2 Transitional versus strict
    • 5.3 Frameset versus transitional
    • 5.4 Summary of specification versions
  • 6 HTML5 variations
    • 6.1 WhatWG HTML versus HTML5
  • 7 Hypertext features not in HTML
  • 8 WYSIWYG editors
  • 9 See also
  • 10 References
  • 11 External links

History


The historic logo made by the W3C

An example website written in HTML Code

Development


Tim Berners-Lee
In 1980, physicist Tim Berners-Lee, who was a contractor at CERN, proposed and prototypedENQUIRE, 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 engineerRobert 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 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-houseStandard 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: "Hypertext Markup Language (HTML)" Internet-Draft by Berners-Lee and Dan Connolly, which included an SGML Document Type Definition to define the grammar.[9]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.[10] 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

January 1997November 24, 1995
HTML 2.0 was published as IETF RFC 1866. Supplemental RFCs added capabilities:
  • November 25, 1995: RFC 1867 (form-based file upload)
  • May 1996: RFC 1942 (tables)
  • August 1996: RFC 1980 (client-side image maps)
  • January 1997: RFC 2070 (internationalization)
HTML 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 in September 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'smarquee 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.
December 1997
HTML 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 1998
HTML 4.0[20] was reissued with minor edits without incrementing the version number.
December 1999
HTML 4.01[21] was published as a W3C Recommendation. It offers the same three variations as HTML 4.0 and its lasterrata were published May 12, 2001.
May 2000
ISO/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]
As of mid-2008, HTML 4.01 and ISO/IEC 15445:2000 were the most recent versions of HTML. Development of the parallel, XML-based language XHTML occupied the W3C's HTML Working Group through the early and mid-2000s.
October 2014
HTML5[24] was published as a W3C Recommendation.[25]

HTML draft version timeline


Logo of HTML5
October 1991
HTML Tags,[6] an informal CERN document listing 18 HTML tags, was first mentioned in public.
June 1992
First informal draft of the HTML DTD,[26] with seven[27][28][29] subsequent revisions (July 15, August 6, August 18, November 17, November 19, November 20, November 22)
November 1992
HTML DTD 1.1 (the first with a version number, based on RCS revisions, which start with 1.1 rather than 1.0), an informal draft[29]
June 1993
Hypertext Markup Language[30] 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[31] one month later, followed by six further drafts published by IETF itself[32] that finally led to HTML 2.0 in RFC1866
November 1993
HTML+ was published by the IETF as an Internet-Draft and was a competing proposal to the Hypertext Markup Language draft. It expired in May 1994.
April 1995 (authored March 1995)
HTML 3.0[33] was proposed as a standard to the IETF, but the proposal expired five months later (28 September 1995)[34] 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.[34]
W3C began development of its own Arena browser as a test bed for HTML 3 and Cascading Style Sheets,[35][36][37] 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]
January 2008
HTML5 was published as a Working Draft (link) by the W3C.[38]
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.[39]
May 2011
On 14 February 2011, the W3C extended the charter of its HTML Working Group with clear milestones for HTML5. In May 2011, the working group advanced HTML5 to "Last Call", an invitation to communities inside and outside W3C to confirm the technical soundness of the specification. The W3C is developing a comprehensive test suite to achieve broad interoperability for the full specification by 2014, which is now the target date for Recommendation.[40]

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,[41] published January 26, 2000, as a W3C Recommendation, later revised and republished 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,[42] published May 31, 2001, as a W3C Recommendation. It is based on XHTML 1.0 Strict, but includes minor changes, can be customized, is reformulated using modules from Modularization of XHTML, which was published April 10, 2001, as a W3C Recommendation.
  • XHTML 2.0 was a working draft, but work on it was abandoned in 2009 in favor of work on HTML5 andXHTML5.[43][44][45] 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.[46]

Markup

HTML markup consists of several key components, including those calledtags (and their attributes), character-based data types, character references and entity references. Another important component of the HTMLdocument type declaration, which triggers standards mode rendering.
The following is an example of the classic Hello world program, a common test employed for comparing programming languages, scripting languages and markup languages. This example is made using 9 lines of code:
<!DOCTYPE html>
<html>
  <head>
    <title>This is a title</title>
  </head>
  <body>
    <p>Hello world!</p>
  </body>
</html>
(The text between <html> and </html> describes the web page, and the text between <body> and </body> is the visible page content. The markup text "<title>This is a title</title>" defines the browser page title.)
The Document Type Declaration <!DOCTYPE html> is for HTML5. If a declaration is not included, various browsers will revert to "quirks mode" for rendering.[47]

Elements[edit]

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> [48]
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:
<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. Note also that "br" is an empty element in that, although it may have attributes, it can take no content and it may not have an end tag.
<p>This <br> is a paragraph <br> with <br> line breaks</p>
This is a link in HTML. To create a link the <a> tag is used. The href= attribute holds the URL address of the link.
<a href="http://www.wikipedia.org/">A link to Wikipedia!</a>
Comments:
<!-- This is a comment -->
Comments can help in the understanding of the markup and do not display in the webpage.
There are several types of markup elements used in HTML:
Structural markup indicates the purpose of text
For example, <h2>Golf</h2> establishes "Golf" as a second-level heading. Structural markup does not denote any specific rendering, but most web browsers have default styles for element formatting. Content may be further styled using Cascading Style Sheets (CSS).[49]
Presentational markup indicates the appearance of the text, regardless of its purpose
For example <b>boldface</b> indicates that visual output devices should render "boldface" in bold text, but gives little indication what devices that are unable to do this (such as aural devices that read the text aloud) should do. In the case of both <b>bold</b> and <i>italic</i>, there are other elements that may have equivalent visual renderings but that are more semantic in nature, such as <strong>strong text</strong> and <em>emphasised text</em>respectively. It is easier to see how an aural user agent should interpret the latter two elements. However, they are not equivalent to their presentational counterparts: it would be undesirable for a screen-reader to emphasize the name of a book, for instance, but on a screen such a name would be italicized. Most presentational markup elements have become deprecated under the HTML 4.0 specification in favor of using CSS for styling.
Hypertext markup makes parts of a document into links to other documents
An anchor element creates a hyperlink in the document and its href attribute sets the link's target URL. For example the HTML markup, <a href="http://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="http://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) .[50][51] Leaving attribute values unquoted is considered unsafe.[52] 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.[53]
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 http://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.[54]

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 &lt; and &amp;, respectively) to be interpreted as character data, rather than markup. For example, a literal < normally indicates the start of a tag, and & normally indicates the start of a character entity reference or numeric character reference; writing it as&amp; or &#x26; or &#38; allows & to be included in the content of an element or in the value of an attribute. The double-quote character ("), when not used to quote an attribute value, must also be escaped as &quot; or &#x22; or&#34; when it appears within the attribute value itself. Equivalently, the single-quote character ('), when not used to quote an attribute value, must also be escaped as &#x27; or &#39; (or as &apos; in HTML5 or XHTML documents[55][56]) 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 forsearch and indexing purposes for example.
Escaping also allows for characters that are not easily typed, or that are not available in the document's character encoding, to be represented within element and attribute content. For example, the acute-accented e (é), a character typically found only on Western European and South American keyboards, can be written in any HTML document as the entity reference &eacute; or as the numeric references &#xE9; or &#233;, using characters that are available on all keyboards and are supported in all character encodings. Unicode 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.[57]

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 theDocument 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:[58]
<!DOCTYPE html>
An example of an HTML 4 doctype
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
This declaration references the DTD for the "strict" version of HTML 4.01. SGML-based validators read the DTD in order to properly parse the document and to perform validation. In modern browsers, a valid doctype activates standards mode as opposed to quirks mode.
In addition, HTML 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[59]

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,[60] 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 whenCascading 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.[61]
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.[62] Such agents are not commonplace even now, but some of the ideas of Web 2.0, mashups andprice 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 byweb 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.[63]
Presentational markup tags are deprecated in current HTML and XHTML recommendations and are illegal in HTML5.
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 theHypertext 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.[64] XHTML 1.1 also states that XHTML 1.1 documents should[65] be labeled with either MIME type.[66]

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.[67]

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


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