XML Pocket Reference

First there was hypertext markup language [HTML] then dynamic hypertext [DHTML]. Now we have XML - extensible markup language. What's the difference between them all? Well, HTML is the basic code for writing web pages. This is the <P>, <BR>, and <A HREF=> stuff which a browser will read as new paragraph, next line, and hyperlink. DHTML added features such as cascading style sheets, font manipulation, and layers. The main point of XML is that it allows you to create your own markup.

It's actually a simplified form of the Standardised General Markup Language (SGML) which makes it a meta-language that enables you to define and format your own document markups. Thus, there are no 'correct' tags for an XML document, except those which you define yourself. This pocket reference offers a quick overview of XML, as well as some sample applications that allow you to get started in coding. The code itself is very similar to HTML, but less forgiving of any mistakes.


It's claimed that the basic concept is simple, but without doubt the coding rapidly becomes complex. The language in which it is discussed makes this readily apparent:

'If you do not specify a name after the XMLNS prefix, the namespace is dubbed the default namespace and is applied to all elements inside the defining element that do not use a namespace prefix of their own.'

As usual with codes which have to be ratified by committees, nothing is for the moment certain or even fixed. All the way through, readers are warned that the code isn't finalised, that something else could replace it, but that the chances are it will look something like this. Unfortunately, this is a state of affairs web page designers have been forced to accommodate, as design code and browser compliance leapfrog through their uneven stages of development

The pocketbook format was something of a departure for O'Reilly Associates when they first appeared. Their other publications are door-stopping reference works of 500 pages plus. But if you want a quick start and a handy tutorial in what Robert Eckstein claims will become the next-generation markup language for the Web, then this is a cheap and compact place to start. The latest edition also introduces XSLT and Xpath.