Whereas I prefer now almost to use my smartphone to do everything except blog on which I usually do on my macbook pros using Firefox as the best browser for what I'm doing here at Blogspot (blogger.com). In this way I can maximize what I can do. i also realized I could send emails from my phone and even pictures and videos through email from my phone during this trip which I hadn't tried before too. However, if you want to do emails and What's App for international communications less expensively you are going to need a smartphone to do that. Also, make sure you research which ones do what the best. Usually all Samsung Androids are international phones and most Iphones are international phones too as long as your service guarantees this. For example, to call South Korea I could get this service for 11 cents a minute for 5 dollars a month service fee through my phone provider. Now I call for free using What's app instead. I also like the feature in What's app that allows me to send pictures to multiple members of my family or even videos or sent links to Internet sites all at once in one shot.
begin quote from:
HTML - Wikipedia
https://en.wikipedia.org/wiki/HTML
Hypertext Markup Language (HTML) is the standard markup language for creating web pages ..... For example, the ID "Attributes" in http://en.wikipedia.org/
HTML - Simple English Wikipedia, the free encyclopedia
https://simple.wikipedia.org/wiki/HTML
HTML can also be used to add meta information to a webpage. ... Cascading Style Sheets (CSS) and JavaScript can be included in HTML code. CSS is used to ...
HTML-Kit - Wikipedia
https://en.wikipedia.org/wiki/HTML-Kit
The Hypertext Transfer Protocol (HTTP) is an application protocol for distributed, collaborative, and hypermedia information systems. HTTP
is the foundation of data communication for the World Wide Web.
Hypertext is structured text that uses logical links (hyperlinks)
between nodes containing text.
Hypertext Transfer Protocol - Wikipedia
https://en.wikipedia.org/wiki/Hypertext_Transfer_Protocol
HTML
From Wikipedia, the free encyclopedia
(Redirected from Html)
 |
|
| Filename extension |
|
|---|---|
| Internet media type | text/html |
| Type code | TEXT |
| Developed by | W3C & WHATWG |
| Initial release | 1993 |
| Latest release | |
| Type of format | Document file format |
| Extended from | SGML |
| Extended to | XHTML |
| Standard |
|
| Open format? | Yes |
| Website | |
| HTML |
|---|
| Comparisons |
HTML elements are the building blocks of HTML pages. With HTML constructs, images and other objects, such as interactive forms, may be embedded into the rendered page. It provides a means to create structured documents by denoting structural semantics for text such as headings, paragraphs, lists, links, quotes and other items. HTML elements are delineated by tags, written using angle brackets. Tags such as
![]()
...
surround and provide information about document text and may include
other tags as sub-elements. Browsers do not display the HTML tags, but
use them to interpret the content of the page.HTML can embed programs written in a scripting language such as JavaScript which affect the behavior and content of web pages. Inclusion of CSS defines the look and layout of content. 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 1997.[2]
Contents
History
The historic logo made by the W3C
An example website written in HTML Code
Development
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.[11] 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.[12]
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.[13]
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).[14] 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.[15]
HTML versions timeline
- November 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)
- January 14, 1997
- HTML 3.2[16] 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.[17]
- Initially code-named "Wilbur",[18] 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.[14] A markup for mathematical formulas similar to that in HTML was not standardized until 14 months later in MathML.
- December 18, 1997
- HTML 4.0[19] 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",[18] 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.[20]
- April 24, 1998
- HTML 4.0[21] was reissued with minor edits without incrementing the version number.
- December 24, 1999
- HTML 4.01[22] 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 2000
- ISO/IEC 15445:2000[23][24] ("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).[23]
- 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.
- October 28, 2014
- HTML5[25] was published as a W3C Recommendation.[26]
- November 1, 2016
- HTML 5.1[27] was published as a W3C Recommendation.[28][29]
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,[30] with seven[31][32][33] 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[33]
- June 1993
- Hypertext Markup Language[34] 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[35] one month later, followed by six further drafts published by IETF itself[36] that finally led to HTML 2.0 in RFC 1866.
- 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[37] was proposed as a standard to the IETF, but the proposal expired five months later (28 September 1995)[38] 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.[38]
- W3C began development of its own Arena browser as a test bed for HTML 3 and Cascading Style Sheets,[39][40][41] 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.[14] 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.[14] (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."[14] 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."[14]
- January 2008
- HTML5 was published as a Working Draft by the W3C.[42]
- 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.[43]
- 2011 HTML5 – Last Call
- On 14 February 2011, the W3C extended the charter of its HTML Working Group with clear milestones for HTML5. In May 2011, the working group advanced HTML5 to "Last Call", an invitation to communities inside and outside W3C to confirm the technical soundness of the specification. The W3C developed a comprehensive test suite to achieve broad interoperability for the full specification by 2014, which was the target date for recommendation.[44] In January 2011, the WHATWG renamed its "HTML5" living standard to "HTML". The W3C nevertheless continues its project to release HTML5.[45]
- 2012 HTML5 – Candidate Recommendation
- In July 2012, WHATWG and W3C decided on a degree of separation. W3C will continue the HTML5 specification work, focusing on a single definitive standard, which is considered as a "snapshot" by WHATWG. The WHATWG organization will continue its work with HTML5 as a "Living Standard". The concept of a living standard is that it is never complete and is always being updated and improved. New features can be added but functionality will not be removed.[46]
- In December 2012, W3C designated HTML5 as a Candidate Recommendation.[47] The criterion for advancement to W3C Recommendation is "two 100% complete and fully interoperable implementations".[48][49]
- 2014 HTML5 – Proposed Recommendation and Recommendation
- In September 2014, W3C moved HTML5 to Proposed Recommendation.[50]
- On 28 October 2014, HTML5 was released as a stable W3C Recommendation,[51] meaning the specification process is complete.[52]
XHTML versions
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[53] 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[54] 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.[55]
- XHTML 2.0 was a working draft, work on it was abandoned in 2009 in favor of work on HTML5 and XHTML5.[56][57][58] 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.[59]
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
and , although some represent empty elements and so are unpaired, for example
![]()
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:
<html>
<head>
<title>This is a title</title>
</head>
<body>
<p>Hello world!</p>
</body>
</html>
<html> and </html> describes the web page, and the text between <body> and </body> is the visible page content. The markup text "The Document Type Declaration
Elements
HTML documents imply a structure of nested HTML elements. These are indicated in the document by HTML tags, enclosed in angle brackets thus:In the simple, general case, the extent of an element is indicated by a pair of tags: a "start tag"
. 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
![]()
Some elements, such as the line break
Many tags, particularly the closing end tag for the very commonly used paragraph element
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
![]()
Element examples
Header of the HTML document: .... The title is included in the head, for example:<head>
<title>The Title</title>
</head>
to
<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>
<p>Paragraph 1</p> <p>Paragraph 2</p>
<p>This <br> is a paragraph <br> with <br> line breaks</p>
href= attribute holds the URL address of the link.<a href="https://www.wikipedia.org/">A link to Wikipedia!</a>
There are several types of markup elements used in HTML:
- Structural markup indicates the purpose of text
- For example,
Golf - Presentational markup indicates the appearance of the text, regardless of its purpose
- For example,
boldfaceindicates 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 bothboldanditalic, there are other elements that may have equivalent visual renderings but that are more semantic in nature, such asstrong textandemphasised textrespectively. 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
hrefattribute sets the link's target URL. For example, the HTML markup,Wikipedia, 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.
Attributes
Most of the attributes of an element are name-value pairs, separated by "=" and written within the start tag of an element after the element's name. The value may be enclosed in single or double quotes, although values consisting of certain characters can be left unquoted in HTML (but not XHTML) .[63][64] Leaving attribute values unquoted is considered unsafe.[65] 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 theismap attribute for the img element.[66]There are several common attributes that may appear in many elements :
- The
idattribute 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" inhttp://en.wikipedia.org/wiki/HTML#Attributes - The
classattribute 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 designationclass="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 exampleclass="notation important"puts the element into both the "notation" and the "important" classes. - An author may use the
styleattribute to assign presentational properties to a particular element. It is considered better practice to use an element'sidorclassattributes to select the element from within a stylesheet, though sometimes this can be too cumbersome for a simple, specific, or ad hoc styling. - The
titleattribute is used to attach subtextual explanation to an element. In most browsers this attribute is displayed as a tooltip. - The
langattribute 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>
abbr, can be used to demonstrate some of these attributes :<abbr id="anId" class="jargon" style="color:purple;" title="Hypertext Markup Language">HTML</abbr>
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.[67]Character and entity references
As of version 4.0, HTML defines a set of 252 character entity references and a set of 1,114,050 numeric character references, both of which allow individual characters to be written via simple markup, rather than literally. 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[68][69])
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.[70]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:[71]
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
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,[72] but has also included presentational markup, such as
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.[73]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.[74] 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.[75]
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
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.[76] XHTML 1.1 also states that XHTML 1.1 documents should[77] be labeled with either MIME type.[78]
HTML e-mail
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.[79]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.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,[80] 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[81] 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:
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:
- The language for an element should be specified with a
langattribute rather than the XHTMLxml:langattribute. XHTML uses XML's built in language-defining functionality attribute. - Remove the XML namespace (
xmlns=URI). HTML has no facilities for namespaces. - Change the document type declaration from XHTML 1.0 to HTML 4.01. (see DTD section for further explanation).
- If present, remove the XML declaration. (Typically this is:
). - Ensure that the document's MIME type is set to
text/html. For both HTML and XHTML, this comes from the HTTPContent-Typeheader sent by the server. - Change the XML empty-element syntax to an HTML style empty element (
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:langandlangattributes 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
- Include explicit close tags for elements that permit content but are left empty (for example,
).
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,noscriptandnoframes
- Inline elements and plain text are allowed directly in:
- 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.)
- underline (
- Presentation related attributes
background(Deprecated. use CSS instead.) andbgcolor(Deprecated. use CSS instead.) attributes forbody(required element according to the W3C.) element.align(Deprecated. use CSS instead.) attribute ondiv,form, paragraph (p) and heading (h1...h6) elementsalign(Deprecated. use CSS instead.),noshade(Deprecated. use CSS instead.),size(Deprecated. use CSS instead.) andwidth(Deprecated. use CSS instead.) attributes onhrelementalign(Deprecated. use CSS instead.),border,vspaceandhspaceattributes onimgandobject(caution: theobjectelement is only supported in Internet Explorer (from the major browsers)) elementsalign(Deprecated. use CSS instead.) attribute onlegendandcaptionelementsalign(Deprecated. use CSS instead.) andbgcolor(Deprecated. use CSS instead.) ontableelementnowrap(Obsolete),bgcolor(Deprecated. use CSS instead.),width,heightontdandthelementsbgcolor(Deprecated. use CSS instead.) attribute ontrelementclear(Obsolete) attribute onbrelementcompactattribute ondl,dirandmenuelementstype(Deprecated. use CSS instead.),compact(Deprecated. use CSS instead.) andstart(Deprecated. use CSS instead.) attributes onolandulelementstypeandvalueattributes onlielementwidthattribute onpreelement
- 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,formandinputelements can be used as a substitute)applet(Deprecated. use theobjectelement instead.)
- The
language(Obsolete) attribute on script element (redundant with thetypeattribute). - Frame related entities
iframenoframestarget(Deprecated in themap,linkandformelements.) attribute ona, client-side image-map (map),link,formandbaseelements
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, withframeset 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.
HTML5 variations
WHATWG HTML versus HTML5
The WHATWG considers their work as living standard HTML for what constitutes the state of the art in major browser implementations by Apple (Safari), Google (Chrome), Mozilla (Firefox), Opera (Opera), and others. HTML5 is specified by the HTML Working Group of the W3C following the W3C process. As of 2013 both specifications are similar and mostly derived from each other, i.e., the work on HTML5 started with an older WHATWG draft, and later the WHATWG living standard was based on HTML5 drafts in 2011.[83][84]Hypertext features not in HTML
HTML lacks some of the features found in earlier hypertext systems, such as source tracking, fat links and others.[85] 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 services or browser manufacturers remedy these shortcomings. For instance, wikis and content management systems allow surfers to edit the Web pages they visit.
WYSIWYG editors
There are some WYSIWYG editors (What You See Is What You Get), in which the user lays out everything as it is to appear in the HTML document using a graphical user interface (GUI), often similar to word processors. The editor renders the document rather than show the code, so authors do not require extensive knowledge of HTML.The WYSIWYG editing model has been criticized,[86][87] primarily because of the low quality of the generated code; there are voices advocating a change to the WYSIWYM model (What You See Is What You Mean).
WYSIWYG editors remain a controversial topic because of their perceived flaws such as:
- Relying mainly on layout as opposed to meaning, often using markup that does not convey the intended meaning but simply copies the layout.[88]
- Often producing extremely verbose and redundant code that fails to make use of the cascading nature of HTML and CSS.
- Often producing ungrammatical markup, called tag soup or semantically incorrect markup (such as
for italics). - As a great deal of the information in HTML documents is not in the layout, the model has been criticized for its "what you see is all you get"-nature.[89]
See also
- Breadcrumb (navigation)
- Comparison of HTML parsers
- Dynamic web page
- HTML decimal character rendering
- List of document markup languages
- List of XML and HTML character entity references
- Microdata (HTML)
- Microformat
- Polyglot HTML
- Semantic HTML
- W3C (X)HTML Validator
References
JavaScript is part of the triad of technologies that all Web developers must learn: HTML to specify the content of web pages, CSS to specify the presentation of web pages, and JavaScript to specify the behaviour of web pages.
- Doug Engelbart's INVISIBLE REVOLUTION . Invisiblerevolution.net. Retrieved on 2012-02-16.
External links
Find more aboutHTMLat Wikipedia's sister projects
Definitions from Wiktionary
Media from Commons
Textbooks from Wikibooks
Learning resources from Wikiversity
Data from Wikidata
Discussion from Meta-Wiki
Documentation from MediaWiki
SGML is very general. HTML is a specific application of the SGML basic syntax applied to hypertext documents with simple structure.
In IETF tradition, standards have to arise from experience with a working prototype implementation — but once they become standards, code that does not conform to them is considered broken and mercilessly scrapped. ...Internet-Drafts are not specifications; software implementers and vendors are specifically barred from claiming compliance with them as if they were specifications. Internet-Drafts are focal points for discussion, usually in a working group... Once an Internet-Draft has been published with an RFC number, it is a specification to which implementers may claim conformance. It is expected that the authors of the RFC and the community at large will begin correcting the specification with field experience.
The hypertext markup language HTML was developed as a simple non-proprietary delivery format for global hypertext. HTML+ is a set of modular extensions to HTML and has been developed in response to a growing understanding of the needs of information providers. These extensions include text flow around floating figures, fill-out forms, tables and mathematical equations.
This document thus defines an HTML 2.0 (to distinguish it from the previous informal specifications). Future (generally upwardly compatible) versions of HTML with new features will be released with higher version numbers.
This document recommends HTML 5.0 after completion.
Note: This working group is closed
XHTML Documents which follow the guidelines set forth in Appendix C, "HTML Compatibility Guidelines" may be labeled with the Internet Media Type "text/html" [RFC2854], as they are compatible with most HTML browsers. Those documents, and any other document conforming to this specification, may also be labeled with the Internet Media Type "application/xhtml+xml" as defined in [RFC3236].
3. SHOULD This word, or the adjective "RECOMMENDED", mean that there may exist valid reasons in particular circumstances to ignore a particular item, but the full implications must be understood and carefully weighed before choosing a different course.
XHTML 1.1 documents SHOULD be labeled with the Internet Media Type text/html as defined in [RFC2854] or application/xhtml+xml as defined in [RFC3236].
Hypertext Transfer Protocol - Wikipedia
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This article needs additional citations for verification. (August 2016) (Learn how and when to remove this template message) |
| Internet protocol suite |
|---|
| Application layer |
| Transport layer |
| Internet layer |
| Link layer |
Hypertext is structured text that uses logical links (hyperlinks) between nodes containing text. HTTP is the protocol to exchange or transfer hypertext.
Development of HTTP was initiated by Tim Berners-Lee at CERN in 1989. Standards development of HTTP was coordinated by the Internet Engineering Task Force (IETF) and the World Wide Web Consortium (W3C), culminating in the publication of a series of Requests for Comments (RFCs). The first definition of HTTP/1.1, the version of HTTP in common use, occurred in RFC 2068 in 1997, although this was obsoleted by RFC 2616 in 1999 and then again by RFC 7230 and family in 2014.
A later version, the successor HTTP/2, was standardized in 2015, and is now supported by major web servers.
Contents
Technical overview
A web browser is an example of a user agent (UA). Other types of user agent include the indexing software used by search providers (web crawlers), voice browsers, mobile apps, and other software that accesses, consumes, or displays web content.
HTTP is designed to permit intermediate network elements to improve or enable communications between clients and servers. High-traffic websites often benefit from web cache servers that deliver content on behalf of upstream servers to improve response time. Web browsers cache previously accessed web resources and reuse them when possible to reduce network traffic. HTTP proxy servers at private network boundaries can facilitate communication for clients without a globally routable address, by relaying messages with external servers.
HTTP is an application layer protocol designed within the framework of the Internet protocol suite. Its definition presumes an underlying and reliable transport layer protocol,[2] and Transmission Control Protocol (TCP) is commonly used. However HTTP can be adapted to use unreliable protocols such as the User Datagram Protocol (UDP), for example in HTTPU and Simple Service Discovery Protocol (SSDP).
HTTP resources are identified and located on the network by Uniform Resource Locators (URLs), using the Uniform Resource Identifiers (URI's) schemes http and https. URIs and hyperlinks in HTML documents form inter-linked hypertext documents.
HTTP/1.1 is a revision of the original HTTP (HTTP/1.0). In HTTP/1.0 a separate connection to the same server is made for every resource request. HTTP/1.1 can reuse a connection multiple times to download images, scripts, stylesheets, etc after the page has been delivered. HTTP/1.1 communications therefore experience less latency as the establishment of TCP connections presents considerable overhead.
History
The first documented version of HTTP was HTTP V0.9 (1991). Dave Raggett led the HTTP Working Group (HTTP WG) in 1995 and wanted to expand the protocol with extended operations, extended negotiation, richer meta-information, tied with a security protocol which became more efficient by adding additional methods and header fields.[5][6] RFC 1945 officially introduced and recognized HTTP V1.0 in 1996.
The HTTP WG planned to publish new standards in December 1995[7] and the support for pre-standard HTTP/1.1 based on the then developing RFC 2068 (called HTTP-NG) was rapidly adopted by the major browser developers in early 1996. By March 1996, pre-standard HTTP/1.1 was supported in Arena,[8] Netscape 2.0,[8] Netscape Navigator Gold 2.01,[8] Mosaic 2.7,[citation needed] Lynx 2.5,[citation needed] and in Internet Explorer 2.0.[citation needed] End-user adoption of the new browsers was rapid. In March 1996, one web hosting company reported that over 40% of browsers in use on the Internet were HTTP 1.1 compliant.[citation needed] That same web hosting company reported that by June 1996, 65% of all browsers accessing their servers were HTTP/1.1 compliant.[9] The HTTP/1.1 standard as defined in RFC 2068 was officially released in January 1997. Improvements and updates to the HTTP/1.1 standard were released under RFC 2616 in June 1999.
In 2007, the HTTPbis Working Group was formed, in part, to revise and clarify the HTTP/1.1 specification. In June 2014, the WG released an updated six-part specification obsoleting RFC 2616:
- RFC 7230, HTTP/1.1: Message Syntax and Routing
- RFC 7231, HTTP/1.1: Semantics and Content
- RFC 7232, HTTP/1.1: Conditional Requests
- RFC 7233, HTTP/1.1: Range Requests
- RFC 7234, HTTP/1.1: Caching
- RFC 7235, HTTP/1.1: Authentication
HTTP session
An HTTP session is a sequence of network request-response transactions. An HTTP client initiates a request by establishing a Transmission Control Protocol (TCP) connection to a particular port on a server (typically port 80, occasionally port 8080; see List of TCP and UDP port numbers). An HTTP server listening on that port waits for a client's request message. Upon receiving the request, the server sends back a status line, such as "HTTP/1.1 200 OK", and a message of its own. The body of this message is typically the requested resource, although an error message or other information may also be returned.[1]HTTP authentication
HTTP provides multiple authentication schemes such as basic access authentication and digest access authentication which operate via a challenge-response mechanism whereby the server identifies and issues a challenge before serving the requested content.HTTP provides a general framework for access control and authentication, via an extensible set of challenge-response authentication schemes, which can be used by a server to challenge a client request and by a client to provide authentication information.[10]
Authentication realms
The HTTP Authentication specification also provides an arbitrary, implementation specific construct for further dividing resources common to a given root URI. The realm value string, if present, is combined with the canonical root URI to form the protection space component of the challenge. This in effect allows the server to define separate authentication scopes under one root URI[10]Request methods
- GET
- The GET method requests a representation of the specified resource. Requests using GET should only retrieve data and should have no other effect. (This is also true of some other HTTP methods.)[1] The W3C has published guidance principles on this distinction, saying, "Web application design should be informed by the above principles, but also by the relevant limitations."[13] See safe methods below.
- HEAD
- The HEAD method asks for a response identical to that of a GET request, but without the response body. This is useful for retrieving meta-information written in response headers, without having to transport the entire content.
- POST
- The POST method requests that the server accept the entity enclosed in the request as a new subordinate of the web resource identified by the URI. The data POSTed might be, for example, an annotation for existing resources; a message for a bulletin board, newsgroup, mailing list, or comment thread; a block of data that is the result of submitting a web form to a data-handling process; or an item to add to a database.[14]
- PUT
- The PUT method requests that the enclosed entity be stored under the supplied URI. If the URI refers to an already existing resource, it is modified; if the URI does not point to an existing resource, then the server can create the resource with that URI.[15]
- DELETE
- The DELETE method deletes the specified resource.
- TRACE
- The TRACE method echoes the received request so that a client can see what (if any) changes or additions have been made by intermediate servers.
- OPTIONS
- The OPTIONS method returns the HTTP methods that the server supports for the specified URL. This can be used to check the functionality of a web server by requesting '*' instead of a specific resource.
- CONNECT
- [16] The CONNECT method converts the request connection to a transparent TCP/IP tunnel, usually to facilitate SSL-encrypted communication (HTTPS) through an unencrypted HTTP proxy.[17][18] See HTTP CONNECT tunneling.
- PATCH
- The PATCH method applies partial modifications to a resource.[19]
Safe methods
Some of the methods (for example, HEAD, GET, OPTIONS and TRACE) are, by convention, defined as safe, which means they are intended only for information retrieval and should not change the state of the server. In other words, they should not have side effects, beyond relatively harmless effects such as logging, caching, the serving of banner advertisements or incrementing a web counter. Making arbitrary GET requests without regard to the context of the application's state should therefore be considered safe. However, this is not mandated by the standard, and it is explicitly acknowledged that it cannot be guaranteed.By contrast, methods such as POST, PUT, DELETE and PATCH are intended for actions that may cause side effects either on the server, or external side effects such as financial transactions or transmission of email. Such methods are therefore not usually used by conforming web robots or web crawlers; some that do not conform tend to make requests without regard to context or consequences.
Despite the prescribed safety of GET requests, in practice their handling by the server is not technically limited in any way. Therefore, careless or deliberate programming can cause non-trivial changes on the server. This is discouraged, because it can cause problems for web caching, search engines and other automated agents, which can make unintended changes on the server.
Idempotent methods and web applications
Methods PUT and DELETE are defined to be idempotent, meaning that multiple identical requests should have the same effect as a single request (note that idempotence refers to the state of the system after the request has completed, so while the action the server takes (e.g. deleting a record) or the response code it returns may be different on subsequent requests, the system state will be the same every time[citation needed]). Methods GET, HEAD, OPTIONS and TRACE, being prescribed as safe, should also be idempotent, as HTTP is a stateless protocol.[1]In contrast, the POST method is not necessarily idempotent, and therefore sending an identical POST request multiple times may further affect state or cause further side effects (such as financial transactions). In some cases this may be desirable, but in other cases this could be due to an accident, such as when a user does not realize that their action will result in sending another request, or they did not receive adequate feedback that their first request was successful. While web browsers may show alert dialog boxes to warn users in some cases where reloading a page may re-submit a POST request, it is generally up to the web application to handle cases where a POST request should not be submitted more than once.
Note that whether a method is idempotent is not enforced by the protocol or web server. It is perfectly possible to write a web application in which (for example) a database insert or other non-idempotent action is triggered by a GET or other request. Ignoring this recommendation, however, may result in undesirable consequences, if a user agent assumes that repeating the same request is safe when it isn't.
Security
The TRACE method can be used as part of a class of attacks known as cross-site tracing; for that reason, common security advice is for it to be disabled in the server configuration.[21] Microsoft IIS supports a proprietary "TRACK" method, which behaves similarly, and which is likewise recommended to be disabled.[21]Summary table
| HTTP Method | RFC | Request Has Body | Response Has Body | Safe | Idempotent | Cacheable |
|---|---|---|---|---|---|---|
| GET | RFC 7231 | No | Yes | Yes | Yes | Yes |
| HEAD | RFC 7231 | No | No | Yes | Yes | Yes |
| POST | RFC 7231 | Yes | Yes | No | No | Yes |
| PUT | RFC 7231 | Yes | Yes | No | Yes | No |
| DELETE | RFC 7231 | No | Yes | No | Yes | No |
| CONNECT | RFC 7231 | Yes | Yes | No | No | No |
| OPTIONS | RFC 7231 | Optional | Yes | Yes | Yes | No |
| TRACE | RFC 7231 | No | Yes | Yes | Yes | No |
| PATCH | RFC 5789 | Yes | Yes | No | No | Yes |
Status codes
In HTTP/1.0 and since, the first line of the HTTP response is called the status line and includes a numeric status code (such as "404") and a textual reason phrase (such as "Not Found"). The way the user agent handles the response primarily depends on the code and secondarily on the other response header fields. Custom status codes can be used since, if the user agent encounters a code it does not recognize, it can use the first digit of the code to determine the general class of the response.[22]The standard reason phrases are only recommendations and can be replaced with "local equivalents" at the web developer's discretion. If the status code indicated a problem, the user agent might display the reason phrase to the user to provide further information about the nature of the problem. The standard also allows the user agent to attempt to interpret the reason phrase, though this might be unwise since the standard explicitly specifies that status codes are machine-readable and reason phrases are human-readable. HTTP status code is primarily divided into five groups for better explanation of request and responses between client and server as named: Informational 1XX, Successful 2XX, Redirection 3XX, Client Error 4XX and Server Error 5XX.
Persistent connections
In HTTP/0.9 and 1.0, the connection is closed after a single request/response pair. In HTTP/1.1 a keep-alive-mechanism was introduced, where a connection could be reused for more than one request. Such persistent connections reduce request latency perceptibly, because the client does not need to re-negotiate the TCP 3-Way-Handshake connection after the first request has been sent. Another positive side effect is that in general the connection becomes faster with time due to TCP's slow-start-mechanism.Version 1.1 of the protocol also made bandwidth optimization improvements to HTTP/1.0. For example, HTTP/1.1 introduced chunked transfer encoding to allow content on persistent connections to be streamed rather than buffered. HTTP pipelining further reduces lag time, allowing clients to send multiple requests before waiting for each response. Another addition to the protocol was byte serving, where a server transmits just the portion of a resource explicitly requested by a client.
HTTP session state
HTTP is a stateless protocol. A stateless protocol does not require the HTTP server to retain information or status about each user for the duration of multiple requests. However, some web applications implement states or server side sessions using for instance HTTP cookies or hidden variables within web forms.Encrypted connections
The most popular way of establishing an encrypted HTTP connection is HTTP Secure.[23] Two other methods for establishing an encrypted HTTP connection also exist: Secure Hypertext Transfer Protocol, and using the HTTP/1.1 Upgrade header to specify an upgrade to TLS. Browser support for these two is, however, nearly non-existent.[24][25][26]Message format
The client and server communicate by sending plain-text (ASCII) messages. The client sends requests to the server and the server sends responses.Request message
The request message consists of the following:- A request line (e.g., GET /images/logo.png HTTP/1.1, which requests a resource called /images/logo.png from the server).
- Request header fields (e.g., Accept-Language: en).
- An empty line.
- An optional message body.
A request line containing only the path name is accepted by servers to maintain compatibility with HTTP clients before the HTTP/1.0 specification in RFC 1945.[28]
Response message
The response message consists of the following:- A status line which includes the status code and reason message (e.g., HTTP/1.1 200 OK, which indicates that the client's request succeeded).
- Response header fields (e.g., Content-Type: text/html).
- An empty line.
- An optional message body.
Example session
Below is a sample conversation between an HTTP client and an HTTP server running on www.example.com, port 80. As mentioned in the previous sections, all the data is sent in a plain-text (ASCII) encoding, using a two-byte CR LF ('\r\n') line ending at the end of each line.Client request
GET /index.html HTTP/1.1
Host: www.example.com
Server response
HTTP/1.1 200 OK
Date: Mon, 23 May 2005 22:38:34 GMT
Content-Type: text/html; charset=UTF-8
Content-Encoding: UTF-8
Content-Length: 138
Last-Modified: Wed, 08 Jan 2003 23:11:55 GMT
Server: Apache/1.3.3.7 (Unix) (Red-Hat/Linux)
ETag: "3f80f-1b6-3e1cb03b"
Accept-Ranges: bytes
Connection: close
<html>
<head>
<title>An Example Page</title>
</head>
<body>
Hello World, this is a very simple HTML document.
</body>
</html>
Most of the header lines are optional. When Content-Length is missing the length is determined in other ways. Chunked transfer encoding uses a chunk size of 0 to mark the end of the content. Identity encoding without Content-Length reads content until the socket is closed.
A Content-Encoding like gzip can be used to compress the transmitted data.
Similar protocols
The Gopher protocol was a content delivery protocol that was displaced by HTTP in the early 1990s. The SPDY protocol is an alternative to HTTP developed at Google, it is superseded by the new HTTP protocol, HTTP/2.See also
| HTTP |
|---|
| Request methods |
| Header fields |
| Status codes |
- Basic access authentication
- Constrained Application Protocol – A semantically similar protocol to HTTP but used UDP or UDP-like messages targeted for devices with limited processing capability. Re-uses HTTP and other internet concepts like Internet media type and web linking (RFC 5988)[31]
- Content negotiation
- Curl-loader – HTTP/S loading and testing open-source software
- Digest access authentication
- Fiddler (software)
- HTTP compression
- HTTP/2 – developed by the IETF's Hypertext Transfer Protocol Bis (httpbis) working group.[32]
- HTTP-MPLEX – A backwards compatible enhancement to HTTP to improve page and web object retrieval time in congested networks proposed by Robert Mattson
- HTTPS
- List of file transfer protocols
- List of HTTP header fields
- List of HTTP status codes
- Representational state transfer (REST)
- Variant object
- Waka (protocol) – An HTTP replacement proposed by Roy Fielding
- Web cache
- WebSocket
- Wireshark
Notes
References
External links
 |
Wikimedia Commons has media related to HTTP. |
- "Change History for HTTP". W3.org. Retrieved 2010-08-01. A detailed technical history of HTTP.
- "Design Issues for HTTP". W3.org. Retrieved 2010-08-01. Design Issues by Berners-Lee when he was designing the protocol.
- "Classic HTTP Documents". W3.org. 1998-05-14. Retrieved 2010-08-01. list of other classic documents recounting the early protocol history
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