Getting Started with HTML5 - HTML, CSS, and Dynamic HTML - page 5

Web Pages and Web Servers
Each document on the World Wide Web is referred to as a Web page and is stored on a
Web server . When you access a Web page, a Web browser retrieves the page from its
Web server and renders it on your computer or other device.
The earliest browsers, known as text-based browsers , were limited to displaying only
text. Today's browsers are capable of handling text, images, audio, video, and interac-
tive programs. In the early days of the Internet, Web browsing was limited to computers.
Now browsers are installed on devices such as mobile phones, cars, handheld media
devices, and gaming systems, to name only a few. How does a Web page work with so
many combinations of browsers and devices? To understand, you need to look at how
Web pages are created.
Introducing HTML
Web pages are text fi les written in Hypertext Markup Language ( HTML) . We've already
discussed hypertext, but what is a markup language? A markup language is a language
that describes the content and structure of a document by identifying, or tagging , dif-
ferent elements in the document. For example, this tutorial contains paragraphs, fi gure
captions, page headings, and so forth; each of these items could be tagged as a distinct
element using a markup language. Thus, HTML is a markup language that supports both
hypertext and the tagging of distinct document elements.
The History of HTML
HTML evolved as the Web itself evolved. Thus, in order to fully appreciate the nuances
of HTML, it's a good idea to review the language's history. The fi rst popular markup
language was the Standard Generalized Markup Language ( SGML ). Introduced in the
1980s, SGML is device- and system-independent, meaning that it can be applied to
almost any type of document stored in almost any format. While powerful, SGML is also
quite complex; for this reason, SGML is limited to those organizations that can afford the
cost and overhead of maintaining complex SGML environments. However, SGML can
also be used to create other markup languages that are tailored to specifi c tasks and are
simpler to use and maintain. HTML is one of the languages created with SGML.
In the early years after HTML was created, no single organization was responsible for
the language. Web developers were free to defi ne and modify HTML in whatever ways
they thought best. This led to incompatibilities between the various browsers and, as a
result, Web page authors faced the challenge of writing HTML code that would satisfy
different browsers and browser versions.
Ultimately, a group of Web designers and programmers called the World Wide Web
Consortium , or the W3C , created a set of standards or specifi cations for all browser
manufacturers to follow. The W3C has no enforcement power; but because using a
uniform language is in everyone's best interest, the W3C's recommendations are usually
followed, though not always immediately. For more information on the W3C and the
services it offers, see its Web site at www.w3.org .
As HTML evolves, earlier features of the language are often deprecated , or phased
out. While deprecated features might not be part of the current specifi cation for HTML,
that doesn't mean that you won't encounter them in your work—indeed, if you are
maintaining older Web sites, you will often need to be able to interpret code from earlier
versions of HTML.