HTML and CSS Reference
Computers don't read text the same way humans do—they can't interpret a string of words and grasp the
concept behind them, they don't see the visual cues we use to separate one group of words from another,
and they can't automatically group related sentences into meaningful paragraphs. Instead of visual cues, a
computer requires a structure composed of clear markers that designate the nature of each portion of text.
That's the essence of a markup language: embedded instructions that a computer can follow in order to
make content readable and usable by humans.
HTML consists of encoded markers called tags that surround and differentiate portions of text, indicating
the function and purpose of the content those tags “mark up.” Tags are embedded directly in a plain-text
document where they can be interpreted by a browser. They're called tags because, well, that's what they
are. Just as a price tag displays the cost of an item and a toe tag identifies a cadaver, so too does an
HTML tag indicate the nature of a portion of content and provide vital information about it. Listing 1-1 is a
very simple bit of HTML, just a heading and a paragraph.
Listing 1-1. An example of text marked up with HTML. The tags are highlighted in bold.
<h1>This is a Level One Heading</h1>
<p>This is a paragraph.</p>
A browser doesn't display the tags themselves; tags only tell the browser how to treat the content between
them. A matched pair of start and end tags (the end tag has a slash) forms an element , comprising the
tags and everything in between them. You'll learn a lot more about tags and elements in Chapter 2, and
you'll learn about the full range of HTML elements throughout the rest of this topic.
From its inception, HTML has been carefully designed to be a simple and flexible language. It's a free,
open standard, not owned or controlled by any company or individual. There is no license to purchase or
specialized software required to author your own HTML documents. Anyone can create and publish web
pages, and it's that very openness that makes the Web the powerful, far-reaching medium it is. HTML
exists so that we can all share information freely and easily.
However, you do need to follow certain rules when you author documents in HTML—there are certain
ways they should be assembled to make certain they'll work properly. The Web runs on agreement, with
all the different authors and programmers and clients and servers agreeing to abide by the same basic
rules, collectively referred to as web standards . Standardizing web languages ensures that the Web can
work consistently and reliably for everyone—users and authors alike. Sticking to the agreed-upon rules
makes communication possible, like the rules of grammar and punctuation that help you understand this
Of course, it follows that someone needs to write down the rules to which we should agree. The technical
specifications for many of the core languages (including HTML) that make up the Web are overseen and
maintained by the World Wide Web Consortium (W3C), an international, non-profit organization founded in
1994 for just this purpose—to standardize the languages and map a clear path for the Web of the future.