2. HTML
HTML or HyperText Markup Language is the standard markup language
used to create web pages.
HTML 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 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).
A web browser can read HTML files and compose them into visible or
audible web pages. The browser does not display the HTML tags, but uses
them to interpret the content of the page. HTML describes the structure of
a website.
3. INTRODUCTION
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 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.
4. HISTORY
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 an Internet-
based hypertext system. 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 from 1990 he listed "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. 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.
5. MARKUP
HTML markup consists of several key components, including tags (and their attributes), character-based data
types, character references and entity references. Another important component is the document 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:
6. ELEMENTS
An HTML element is an individual component of an HTML document or web page, once this has been parsed
into the Document Object Model. HTML is composed of a tree of HTML elements and other nodes, such as text
nodes. Each element can have HTML attributes specified. Elements can also have content, including other
elements and text. HTML elements represent semantics, or meaning. For example, the title element represents
the title of the document.
In the HTML syntax, most elements are written with a start tag and an end tag, with the content in between. An
HTML tag is composed of the name of the element, surrounded by angle brackets. An end tag also has a slash
after the opening angle bracket, to distinguish it from the start tag. For example, a paragraph, which is
represented by the p element, would be written as:
7. HTML 5
HTML5 is a core technology markup language of the Internet used for structuring and
presenting content for the World Wide Web. As of October 2014 this is the final and
complete fifth revision of the HTML standard of the World Wide Web Consortium
(W3C).
Its core aims have been to improve the language with support for the latest
multimedia while keeping it easily readable by humans and consistently understood
by computers and devices (web browsers, parsers, etc.). HTML5 is intended to
subsume not only HTML 4, but also XHTML 1 and DOM Level 2 HTML.
8. XHTML
Extensible Hypertext Markup Language (XHTML) is a family of XML markup languages that mirror or extend
versions of the widely used Hypertext Markup Language (HTML), the language in which Web pages are
formulated.
While HTML, prior to HTML5, was defined as an application of Standard Generalized Markup Language (SGML),
a flexible markup language framework, XHTML is an application of XML, a more restrictive subset of SGML.
XHTML documents are well-formed and may therefore be parsed using standard XML parsers, unlike HTML,
which requires a lenient HTML-specific parser
9. XHTML V/S HTML
There are various differences between XHTML and HTML. The Document Object Model (DOM) is a tree structure
that represents the page internally in applications, and XHTML and HTML are two different ways of representing
that in markup (serializations). Both are less expressive than the DOM (for example, "--" may be placed in
comments in the DOM, but cannot be represented in a comment in either XHTML or HTML), and generally
XHTML's XML syntax is a little more expressive than HTML (for example, arbitrary namespaces are not allowed in
HTML). First off, one source of differences is immediate: XHTML uses an XML syntax, while HTML uses a pseudo-
SGML syntax (officially SGML for HTML 4 and under, but never in practice, and standardised away from SGML in
HTML5). Secondly however, because the expressible contents of the DOM in syntax are slightly different, there
are some changes in actual behavior between the two models.
10. XHTML5 (XML-serialized HTML5)
XML documents must be served with an XML Internet media type (often called "MIME type") such as
application/xhtml+xml or application/xml, and must conform to strict, well-formed syntax of XML. XHTML5 is
simply a XML-serialized HTML5 data (e.g. not having any unclosed tags), sent with one of XML media types.
HTML that has been written to conform to both the HTML and XHTML specifications — and which will therefore
produce the same DOM tree whether parsed as HTML or XML — is termed "polyglot markup".
HTML5 has both a regular text/html serialization and an XML serialization, which is also known as XHTML5. The
language is more compatible with HTML 4 and XHTML 1.x than XHTML 2.0, due to the decision to keep the
existing HTML form elements and events model. It adds many new elements not found in XHTML 1.x, however,
such as section and aside tags.
11. Hypertext features not in HTML
HTML lacks some of the features found in earlier hypertext systems, such as source tracking, fat links and others.
Even some hypertext features that were in early versions of HTML have been ignored by most popular web
browsers until recently, 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.