Introduction

Truly ambitious programmers are never satisfied with what they are given and are obsessively driven to enhance what they have. I say "ambitious" rather than "great" because greatness, in my opinion, comes from knowing when it is wiser to work within the system versus when it is best to extend the system. Nevertheless, this chapter is dedicated to extending the system both from the perspective of XSLT needing functionality best implemented in another language and from the perspective of other languages needing XSLT.

Extending XSLT is, by definition, a facility on the fringes of the specification. Extensions decrease the portability of an XSLT stylesheet. This is definitely a hazard when you use extensions provided natively by your XSLT processor or when implementing your own extension. It is true even if you implement your extensions in a highly portable language like Java. The most obvious reason is that some XSLT processors are not written in Java and are thus unlikely ever to support Java-based extensions. However, even if you only want your extensions to work in Java-based XSLT processors, you might still run into trouble because the extension mechanism of XSLT was not fully standardized in Version 1.0. This state of affairs improved in Version 1.1, but 1.1 is no longer an official XSLT release and many processors do not support it. Surprisingly, XSLT 2.0 took a step back from 1.1 by leaving the method of binding extension functions undefined.

EXSLT.org is a portal whose supporters are dedicated to establishing standards XSLT implementers can follow when implementing common extensions. Chapter 2 and Chapter 3 mentioned EXSLT with respect to math extensions and date extensions. EXSLT.org also organized other extension categories, some of which this chapter touches upon. It is certainly a site worth visiting before going off and implementing your own extension. There is a good chance that someone either developed such an extension or put some thought into how the extension should work.

In contrast to extending XSLT, embedding XSLT involves invoking XSLT transformations from another language without forking your XSLT processor in a separate process. You will see how XSLT can be accessed from within Java- and Perl-based programs.

When writing this chapter, it quickly became apparent that you could easily dedicate a whole book to extension and embeddingespecially when you consider the cross between implementations, extension languages, and interesting examples. To keep this chapter manageable, I compromised by alternating between Xalan-Java 2 and Saxon and sticking mostly to Java and JavaScript. This chapter also discusses MSXML.

To prevent repetition, this section explains how to use extensions in Saxon, Xalan-Java 2, and MSXML.