XHTML

What You Should Already Know
Before you continue you should have a basic understanding of the following:
HTML and the basics of building web pages
If you want to study HTML first, please read our HTML tutorial.
What Is XHTML?
XHTML stands for EXtensible HyperText Markup Language
XHTML is almost identical to HTML 4.01
XHTML is a stricter and cleaner version of HTML
XHTML is HTML defined as an XML application
XHTML is a W3C Recommendation
XHTML is a W3C Recommendation
XHTML 1.0 became a W3C Recommendation January 26, 2000.
Stay updated with the latest W3C recommendations in our W3C tutorial.
All New Browsers Support XHTML
XHTML is compatible with HTML 4.01.
All new browsers have support for XHTML.

What is XML

• XML stands for EXtensible Markup Language


• XML is a markup language much like HTML


• XML was designed to carry data, not to display data


• XML tags are not predefined. You must define your own tags


• XML is designed to be self-descriptive


• XML is a W3C Recommendation

The Difference Between XML and HTML

XML is not a replacement for HTML.
XML and HTML were designed with different goals:

XML was designed to transport and store data, with focus on what data is.
HTML was designed to display data, with focus on how data looks.

HTML is about displaying information, while XML is about carrying information.
XML Does not DO Anything

Maybe it is a little hard to understand, but XML does not DO anything. XML was created to structure, store, and transport information.

The following example is a note to Tove from Jani, stored as XML:
The following example is a note to Tove from Jani, stored as XML:

The note above is quite self descriptive. It has sender and receiver information, it also has a heading and a message body.

But still, this XML document does not DO anything. It is just pure information wrapped in tags. Someone must write a piece of software to send, receive or display it.

XML is Just Plain Text
XML is nothing special. It is just plain text. Software that can handle plain text can also handle XML.

However, XML-aware applications can handle the XML tags specially. The functional meaning of the tags depends on the nature of the application.
With XML You Invent Your Own Tags

The tags in the example above (like and ) are not defined in any XML standard. These tags are "invented" by the author of the XML document.

That is because the XML language has no predefined tags.

The tags used in HTML (and the structure of HTML) are predefined. HTML documents can only use tags defined in the HTML standard (like, , etc.).

XML allows the author to define his own tags and his own document structure.
XML is Not a Replacement for HTML

XML is a complement to HTML.

It is important to understand that XML is not a replacement for HTML. In most web applications, XML is used to transport data, while HTML is used to format and display the data.

My best description of XML is this:
XML is a software and hardware independent tool for carrying information.

XML is a W3C Recommendation

The Extensible Markup Language (XML) became a W3C Recommendation 10. February 1998.

XML is Everywhere

We have been participating in XML development since its creation. It has been amazing to see how quickly the XML standard has developed and how quickly a large number of software vendors have adopted the standard.

XML is now as important for the Web as HTML was to the foundation of the Web.

XML is everywhere. It is the most common tool for data transmissions between all sorts of applications, and becomes more and more popular in the area of storing and describing information.

How Can XML be Used?

XML is used in many aspects of web development, often to simplify data storage and sharing.

XML Separates Data from HTML
If you need to display dynamic data in your HTML document, it will take a lot of work to edit the HTML each time the data changes.

With XML, data can be stored in separate XML files. This way you can concentrate on using HTML for layout and display, and be sure that changes in the underlying data will not require any changes to the HTML.

With a few lines of JavaScript, you can read an external XML file and update the data content of your HTML.
You will learn more about this in a later chapter of this tutorial.

XML Simplifies Data Sharing

In the real world, computer systems and databases contain data in incompatible formats.
XML data is stored in plain text format. This provides a software- and hardware-independent way of storing data.
This makes it much easier to create data that different applications can share.

XML Simplifies Data Transport

With XML, data can easily be exchanged between incompatible systems.
One of the most time-consuming challenges for developers is to exchange data between incompatible systems over the Internet.
Exchanging data as XML greatly reduces this complexity, since the data can be read by different incompatible applications.

XML Simplifies Platform Changes

Upgrading to new systems (hardware or software platforms), is always very time consuming. Large amounts of data must be converted and incompatible data is often lost.
XML data is stored in text format. This makes it easier to expand or upgrade to new operating systems, new applications, or new browsers, without losing data.

XML Makes Your Data More Available

Since XML is independent of hardware, software and application, XML can make your data more available and useful.
Different applications can access your data, not only in HTML pages, but also from XML data sources.
With XML, your data can be available to all kinds of "reading machines" (Handheld computers, voice machines, news feeds, etc), and make it more available for blind people, or people with other disabilities.

XML is Used to Create New Internet Languages
A lot of new Internet languages are created with XML.
Here are some examples:
XHTML the latest version of HTML
WSDL for describing available web services
WAP and WML as markup languages for handheld devices
RSS languages for news feeds
RDF and OWL for describing resources and ontology
SMIL for describing multimedia for the web

If Developers Have Sense
If they DO have sense, future applications will exchange their data in XML.
The future might give us word processors, spreadsheet applications and databases that can read each other's data in a pure text format, without any conversion utilities in between.

XML Tree

A Brief History of Javascript

When the World Wide Web was first created in the early 1990s all web pages were static. When you viewed a web page you saw exactly what the page was set up to show you and there was no way for you to interact with the page.

Being able to interact with a web page - have it do something in response to your actions - required the addition of some form of programming language to "instruct" the page how it should respond to your actions. In order to have it respond immediately without having to reload the web page this language needed to be able to run on the same computer as the browser displaying the page.

At the time there were two browsers that were reasonably popular - Netscape Navigator and Internet Explorer. Netscape was the first to bring out a programming language that would allow web pages to become interactive - they called it Livescript and it was integrated into the browser (meaning that the browser would interpret the commands directly without requiring the code to be compiled and without requiring a plugin to be able to run it). This meant that anyone using the latest Netscape browser would be able to interact with pages that made use of this language.

Another programming language called Java (which required a separate plugin in order to run) became very well known and so Netscape decided to try to cash in on this by renaming the language built into their browser to Javascript. Note that while some Java and Javascript code may appear similar, they are in fact two entirely different languages that serve completely different purposes.

Not to be left behind Internet Explorer was soon updated to support not one but two integrated languages. One was called vbscript and was based on the BASIC programming language and the other was called Jscript and was very similar to Javascript. In fact if you were very careful what commands you used you could write code that would be able to be processed as Javascript by Netscape Navigator and as Jscript by Internet Explorer.

At the time Netscape Navigator was by far the more popular browser and so later versions of Internet Explorer implemented versions of Jscript that were more and more like Javascript. By the time that Internet Explorer became the dominant browser Javascript had become the accepted standard for writing interactive processing to be run in the web browser.

The importance of this scripting language was too great to leave its future development in the hands of the competing browser developers and so in 1996 Javascript was handed over to an international standards body called ECMA who then became responsible for the subsequent development of the language.

What Is CSS?

Have you ever thought about what a web page is? I mean, what it really is? Some people think of a web page as a visual medium—an aesthetically pleasing experience which may or may not contain information that’s of interest to the viewer. Other people think of a web page as a document that may be presented to readers in an aesthetically pleasing way. From a technical point of view, the document interpretation is more appropriate.
When we examine the elements of its construction, a web document can consist of up to three layers—content, presentation, and behavior—as illustrated in Figure 1.
The content layer is always present. It comprises the information the author wishes to convey to his or her audience, and is embedded within HTML or XHTML markup that defines its structure and semantics. Most of the content on the Web today is text, but content can also be provided through images, animations, sound, video, and whatever else an author wants to publish.
The presentation layer defines how the content will appear to a human being who accesses the document in one way or another. The conventional way to view a web page is with a regular web browser, of course, but that’s only one of many possible access methods. For example, content can also be converted to synthetic speech for users who have impaired vision or reading difficulties.
Figure 1. The three layers of a web document
The behavior layer involves real-time user interaction with the document. This task is normally handled by JavaScript. The interaction can be anything from a trivial validation that ensures a required field is filled in before an order form can be submitted, to sophisticated web applications that work much like ordinary desktop programs.
It’s possible to embed all three layers within the same document, but keeping them separate gives us one valuable advantage: we can modify or replace any of the layers without having to change the others.
Certain versions of HTML and XHTML also contain presentational element types—that is, elements that specify the appearance of the content, rather than structure or semantics. For example, and can be used to control the presentation of text, and

---

will insert a visible rule element. However, as these types of elements embed presentation-layer information within the content layer, they negate any advantage we may have gained by keeping the layers separate.
Cascading Style Sheets, or CSS, is the recommended way to control the presentation layer in a web document. The main advantage of CSS over presentational HTML markup is that the styling can be kept entirely separate from the content. For example, it’s possible to store all the presentational styles for a 10,000-page web site in a single CSS file. CSS also provides far better control over presentation than do presentational element types in HTML.
By externalizing the presentation layer, CSS offers a number of significant benefits:
All styling is kept in a limited number of style sheets. The positive impact this has on site maintenance can’t be overestimated—editing one style sheet is obviously more efficient than editing 10,000 HTML files!
The overall saving in bandwidth is measurable. Since the style sheet is cached after the first request and can be reused for every page on the site, it doesn’t have to be downloaded with each web page. Removing all presentational markup from your web pages in favor of using CSS also reduces their size and bandwidth usage—by more than 50% in many documented cases. This benefits the site owner, through lower bandwidth and storage costs, as well as the site’s visitors, for whom the web pages load faster.
The separation of content from presentation makes it easier for site owners to reuse the content for other purposes, such as RSS feeds or text-to-speech conversion.
Separate styling rules can be used for different output media. We no longer need to create a special version of each page for printing—we can simply create a single style sheet that controls how every page on the site will be printed.
Although CSS is designed to be independent of the markup language of the documents to which it is applied, in reality, it’s used mainly with HTML and XML (including XHTML).

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html
In this HTML tutorial you will learn how to use HTML to create your own Web site.
HTML is very easy to learn!
XHTML is a stricter and cleaner version of HTML.
In this tutorial you will learn the difference between HTML and XHTML. We will also show you how this Web site was converted to XHTML.

XML stands for EXtensible Markup Language.
XML was designed to transport and store data.
In this tutorial you will learn about XML, and the difference between XML and HTML.
XML is important to know, and very easy to learn.

Save a lot of work with CSS!
In our CSS tutorial you will learn how to use CSS to control the style and layout of multiple Web pages all at once.

JavaScript is THE scripting language of the Web.
JavaScript is used in millions of Web pages to add functionality, validate forms, detect browsers, and much more.
JavaScript is easy to learn! You will enjoy it!