The proposal will allow a child classloader to override class definitions from
its parent classloader. This functionality will be useful for RMI, for
standard extensions (javax.*), and for External Standards.

For example, this will allow an applet to use its own preferred version of a
standard extension, even if some other version is already installed on the
client system.

Considering a specific example, a third party will be able to override the
version of the XML SAX or XML DOM APIs provided as part of J2SE in
order to use a later revision of those APIs.