Carlos.Lucasius@Canada (April/May, 2001):

Aimed at the next feature releases of Java Web Start and higher (2.0+),
the JPDA Compliant Debugging Extension to Java Web Start -- or simply
"debugging extension" hereafter for brevity -- enables Java Web Start
developers, Java Web Start applications developers, and Java Web Start
licensees to dynamically trace through both the Java code underlying
Web Start and the Java code underlying any Java application that it may
launch, and in doing so to (1) better stay on top of the semantics of
the relevant Java code as it evolves over time (towards new product
releases), and (2) more easily locate any bugs that may still exist
anywhere in this code at any time. Thus, for developers of products
that depend on Java Web Start, the debugging extension offers the
potential benefit of not only improved product quality, but also of
increased efficiency (compression of the product development cycle)
and hence enhanced productivity.

For further information, please read:

file:/net/altair.east/export/space5/javaws/jpda/@intro.txt

which also contains pointers to the code changes.