See http://www.saxproject.org for more information about SAX.
The package is independent of the SAX2 core, though the functionality exposed generally needs to be implemented within a parser. That independence has several consequences:
SAX2 drivers are not required to recognize these handlers, and you cannot assume that the class files will be present in every SAX2 installation.
This package may be updated independently of SAX2 (i.e. new handlers may be added without updating SAX2 itself).
The handlers are not implemented by the SAX2
org.xml.sax.helpers.XMLFilterImpl class.
You can subclass these if you need such behaviour.
The handlers need to be registered differently than regular SAX2 handlers.
This package, SAX2-ext, is a standardized extension to SAX2. It is designed both to allow SAX parsers to pass certain types of information to applications, and to serve as a simple model for other SAX2 parser extension packages. Not all such extension packages should need to be recognized directly by parsers, however. As an example, most schema systems can be cleanly layered on top of parsers supporting the standardized SAX2 interfaces.
Note: this package alone does add any functionality; it simply provides optional interfaces for SAX2 drivers to use. You must use a SAX2 driver that recognizes these interfaces if you actually want to have access to lexical and declaration information.
Note: The original documentation comes from SAX 2.0.