HyperText Markup Language and Cascading Style Sheets
HyperText Markup Language (HTML) is the main markup language for creating web pages and other information that can be displayed in a web browser.
HTML 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 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 appearance 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.
CSS,
or Cascading Style Sheets, are used to describe the visual style and
presentation of a document, most commonly web sites. One of the purposes
of CSS is to separate the presentation of a document from the structure
and content (although it is possible to embed CSS within the structure
as well), and is a W3C
recommendation. Separation of style from structure and content
increases maintainability for the author(s) of a document as well as
accessibility for the audience. CSS is commonly applied to HTML, XHTML and XML documents, though it is possible, albeit rare, to apply it to other types of documents as well.
CSS is one way of describing the "style" -- the colors, fonts,
layout, and other "presentation" aspects of a document. A single CSS
file can describe a common "style" to be applied to many HTML, XHTML,
and XML documents (which describe the content and structure of the
elements of each document). Typically a particular element in a XHTML
file has a "cascade" of CSS style rules that can be applied to it. The
highest priority style rule is applied to each element.
Why would I want to use CSS rather than something else?
CSS is a powerful tool that gives web designers flexibility and modularity in the presentation layer of a web site.
CSS allows you to have every format rule defined for later use
(here "format" means how things appear). So if you are writing a large
website and you want a consistent appearance for every title, sub-title,
how examples of code appear, how paragraphs are aligned, (I could go
on, CSS covers a wide range of presentation options) then CSS is the way
to go.
Let's say you have a 1200 page website that took you months to
complete. Your current boss gets a promotion and another person fills
his place. Your new boss says to change the font, the size, the
background, the appearance of tables, etc. everywhere on your
1200-page site to comply with some new corporate policy. If you
engineered your site appropriately with CSS, you could do this by
editing one linked CSS file that has all
your appearance (format) rules in one place. Or you could do it the
hard way, and hammer the appearance changes on each and every one of
your 1200 HTML pages. By using CSS, changes can be made fast and easy
simply by editing a few rules and lines in the global stylesheet. Before
CSS was used, these changes were more difficult, expensive, and very
time-consuming.
Some server-side template systems can largely be used for the same
purpose. Unlike CSS, however, they most often separate the structure
from the content and not the presentation from the structure, making it
much more difficult for users who wish to disable or ignore styling to
do so.
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