HTML and CSS Reference
the incoming request, applying defaults and rewriting rules. It determines
whether to satisfy the request by returning the contents of a ile or by execut-
ing a program and returning the output. If the requested resource requires
authentication, Apache returns a status code instructing the browser to
resubmit the request ater prompting for a username/password combination.
he HTTP request contains additional information such as the name of the
browser or user agent and the preferred language. his enables Apache to
provide a diferent page for mobile users or to substitute a translation of the
requested page if one is available.
Web browsers and servers speak many other Internet protocols. Browsers
are, in a sense, the Swiss army knives of Internet clients. Web servers have
plug-in interfaces to email, database, FTP, streaming video players, and other
services. Web servers can also make requests to each other and serve as mir-
rors or proxies for each other.
his section contains a lot of acronyms and deinitions. Much of the descrip-
tive material is taken from Wikipedia. In a very real sense, Wikipedia rep-
resents the current usage and understanding of these terms by the Web
community. I've listed them in order of decreasing importance, or their
likelihood of ever coming up in casual conversation. his list is by no means
HTML (HyperText Markup Language) he predominant markup
language for web pages. It provides a means to create structured docu-
ments using semantic tags for such things as headings, paragraphs, lists,
links, quotes, and other items. It lets you embed images and other media
objects and can be used to create interactive forms.
CSS (Cascading Style Sheets) he language for describing the presen-
tation (that is, the formatting and layout) of an HTML document. CSS is
designed to enable the separation of document content from the details
of how it should be presented, including the typography, positioning,
colors, and margins. his separation improves content accessibility and
provides more lexibility in controlling presentation characteristics.
version that runs inside a user's browser and manipulates HTML page