# GNU JAXP XSL transformer

This package contains a Java XSL transformer compliant with the JAXP specification. It depends on the GNU DOM and XPath implementations, and will generate GNU DOM nodes unless a specific target from another implementation was given. It understands DOM, SAX, and stream sources and result sinks and supports these JAXP features.
To use this transformer, set the system property `javax.xml.transform.TransformerFactory` to the value `gnu.xml.transform.TransformerFactoryImpl`. You can then instantiate TransformerFactory and transformers in the ordinary manner. Reuse of stylesheets is supported using the JAXP Templates mechanism.

### Architecture

When given a stylesheet source, this implementation compiles it internally into a Stylesheet object, which is a container for templates and state. Each stylesheet instruction is represented by a subclass of TemplateNode, which is arranged in a directed graph: each TemplateNode has a reference to its first child and the next node.
The transformation process consists of identifying the Template that matches the root of the source context, and calling `apply` on its corresponding TemplateNode. This in turn processes its children and next TemplateNode, depending on the semantics of each node type.
Template nodes may reference XPath expressions or patterns. These are fully compiled to objects of type Expr at the time the stylesheet is compiled.

### Conformance

This implementation is feature complete, but the XSLT specification is large and there are still many bugs that need to be ironed out. It has been tested against the OASIS XSLT TC test suite, comprising unit tests from the Xalan project and Microsoft. Conformance to these unit tests is approximately 70% at the current time, although normal usage of the transformer should involve relatively few surprises (the test suite is designed to test very complex and obscure functionality).

### Known bugs

- When reusing stylesheets using the JAXP Templates mechanism, XSL `apply-imports` instructions will not work.
- XPath filter expressions do not always work as expected (this is a problem with the GNU XPath implementation rather than the transformer). This can result in problems with the `position()` function, as well as `select` expressions and numbering.

Obviously we'd like to improve conformance and fix these bugs. If you're interested in working on any of these issues please contact us.