HTML or HyperText Markup Language is
the main markup
language for creating web
pages and other information that can be
displayed in a web
browser.
SHTML is written
in the form of HTML
elements consisting of tags enclosed
in angle
brackets (like <html>), within the
web page content. HTML tags most commonly come
in pairs like <h1> and </h1>, although some
tags represent empty elements and so are
unpaired, for example <img>. The first tag in a pair is the start
tag, and the second tag is the end tag (they
are also called opening tags and closing
tags). In between these tags web designers
can add text, further tags, comments and
other types of text-based content.
The purpose of
a web
browser is to read HTML documents and
compose them into visible or audible web pages.
The browser does not display the HTML tags, but
uses the tags to interpret the content of the
page.
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 scriptswritten
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 W3C,
maintainer of both the HTML and the CSS
standards, encourages the use of CSS over
explicit presentational HTML.[1]
In 1980,
physicist Tim
Berners-Lee, who was a contractor at CERN,
proposed and prototyped ENQUIRE,
a system for CERN researchers
to use and share documents. In 1989, Berners-Lee
wrote a memo proposing anInternet-based hypertext system.[2] Berners-Lee
specified HTML and wrote the browser and server
software in late 1990. That year, Berners-Lee
and CERN data systems engineer Robert
Cailliau collaborated on a joint request for
funding, but the project was not formally
adopted by CERN. In his personal notes[3] from
1990 he listed[4] "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.[5][6] 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 SGML-based
documentation format at CERN. Eleven of these
elements still exist in HTML 4.[7]
HyperText
Markup Language 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 9537Techniques 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.[8] 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.[9] 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.[10]
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.[11]
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).[12] 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.
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>
In
the simple, general case, the extent of an
element is indicated by a pair of tags: a 'start
tag' <p> and
'end 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 <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
