HTML and CSS Reference
In-Depth Information
Robots
are a very important class of Web user. hey are automated
computer programs that run on Internet servers and visit web
pages the same way people do using a browser. But instead of
presenting the page, the robot analyzes it, stores information about
the page in a database, and decides what page to visit next using
that information. his is how Google, Yahoo!, Bing, and other
search engines work. Other robots perform similar data collection for market-
ing and academic purposes. Robots are oten called “spiders” because of how
they seem to “crawl” over the Web from one link to the next. Also, there are
malicious robots. hese automatic programs leave spam comments on blogs or
look for security loopholes to gain control of resources with which they should
not be messing.
Bad robots!
When creating content for the Web, you generally are not concerned with
any of this. Most of the HTML structure that deals with browsers, robots,
and widgets is supplied by the Web editing sotware you use or by server-side
scripts and template systems. If you are editing content directly online, all you
need to understand is how to mark up the content with simple HTML ele-
ments. Web developers—that is, programmers as opposed to authors—need
to fully understand how these three principal components—HTML, CSS, and
scripting—work together to form the framework of the Web (see Figure 1.2).
Figure 1.2: The three components of a web page
By the way, did I mention that all of this is essentially
free
? It is free in
two senses of the word. It's free because there is no acquisition cost, and free
because you can use it for your own purposes. With only minor limitations, all
the HTML, CSS, and scripting that go into a Web page are available for you to
examine, copy, and reuse.
Tim Berners-Lee
, the inventor of HTML, the URL,
and the HTTP protocol that web servers and user agents use to talk to each
other, put all these components into the public domain. Working at CERN, the
European Center for Nuclear Research, he was trying to ind a better way for
large teams of researchers, working in diferent countries with diferent word
