Why XSL?

With so many stylesheet languages already in existence, there has to be a good reason why a new one is needed. Indeed, some have argued that XSL is not necessary. However, there were valid reasons for the development of this language.

First, XSL has an obvious advantage over the vast array of product-specific stylesheet languages. As an industry standard, it is beginning to be supported by a wide range of tools, deployed on a wide range of computer platforms. A number of browser and publishing applications are being modified to accept XSL-styled documents for presentation, so removing dependence on a particular supplier. These are, of course, benefits complementary to the use of XML itself. However, this still leaves a small number of existing standards to discuss.

The CSS (Cascading StyleSheet language) format is widely used, in part as a consequence of the fact that the popular Web browser vendors have added support for this language. CSS was originally developed explicitly to complement HTML. At first sight this seems strange, as HTML comprises a large number of format-specific tags and so a stylesheet is not actually necessary. In fact, CSS was initially introduced to give Web page authors more control over format; it was simply a way to override the browser's default formatting settings, and in its simplest form the format instructions are not even stored in a separate stylesheet at all, but in an HTML attribute called 'Style'. CSS can be used with XML, and some have argued that CSS is sufficient for this task. But XSL is far more powerful than CSS, as this book aims to show, and the task of learning both has been simplified by the adoption of CSS-style property names in XSL.

The DSSSL standard has been a major influence on the development of XSL, despite a dramatic difference in appearance. The initial impetus for the development of XSL came from a desire to replicate the power of DSSSL in a language that had a simpler, XML-based, syntax.

It is instructive to look back at XML and see why it has become such a success, as the stylesheet story may hold some interesting parallels. XML was introduced to fill a gap between the simple but limited HTML format and the powerful but complex SGML format. Likewise, XSL is intended to sit between the simple but limited CSS format and the powerful but complex DSSSL format.