SAXONICA

Saxon Documentation
Full Contents
About Saxon
Changes in this Release
Conditions of Use
Using XSLT 2.0
Using XQuery
Handling Source Documents
XML Schema Processing
XPath API for Java
| Introduction
» | The JAXP XPath API
| The Standalone XPath API
| The NodeInfo Object
| Building the Source Document
Saxon on .NET
Extensibility
Saxon Extensions
Sample Saxon Applications
The Saxon SQL Extension
XSLT Elements
XPath 2.0 Expression Syntax
Function Library
Standards Conformance

# Context node

Many of the methods in the JAXP interface take an argument to represent the context node. Because the API is designed to be used with multiple object models, this is typed simply as an `Object`. In the case of Saxon, this can be an object in any of the supported data models: DOM, JDOM, DOM4J, XOM, or Saxon's native `NodeInfo` representation. Note that if a `NodeInfo` is supplied, the tree must have been constructed using the same Saxon `Configuration` as the one used by the `XPathEvaluator` itself.

Many of these methods specify that if the context node supplied is null, the XPath expression will be evaluated using an empty document node as the context node. Saxon does not implement this rule. There are two reasons for this. Firstly, it's unnatural in XPath 2.0, where it is permissible for the context item for an expression to be undefined. Secondly, it's not clear what kind of document node it would be appropriate to create, given that Saxon supports multiple object models. Instead, if null is supplied, then the node supplied to the Saxon-specific method `setContextNode()` is used, and if that is null, the expression is evaluated with the context item undefined (which will cause a dynamic error if the expression actually refers to the context item).

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