Packages in the SAX2 API (SAX2)

1.5. Packages in the SAX2 API

SAX2 consists of three packages:

org.xml.sax: This package contains the core SAX interfaces and exceptions, plus two concrete classes. The package has SAX1 as well as SAX2 support.
org.xml.sax.helpers: As suggested by its name, this package exists to help applications use the SAX core. Most of its classes are utility implementations of core interfaces (except the parser interfaces), but the portable bootstrap APIs are also part of this package. SAX2 added to what SAX1 started.
org.xml.sax.ext: This package holds the SAX2 extension handlers, described earlier, and will probably grow to hold other SAX2 extensions in the future.

Only the org.xml.sax package is guaranteed to be part of every SAX distribution. The helpers don't depend on the extensions, to preserve this notion of "core plus options." In practice, it's a rare distribution that doesn't include all of these packages, and SAX2 parsers without support for the extension handlers are likely to support only XML subsets. JAXP 1.1 (and hence JDK 1.4) includes all three packages.