How does the SharedSecrets mechanism work?

jdk.internal.misc.SharedSecrets describes itself as:

A repository of “shared secrets”, which are a mechanism for
calling implementation-private methods in another package without
using reflection. A package-private class implements a public
interface and provides the ability to call package-private methods
within that package; the object implementing that interface is
provided through a third package to which access is restricted.
This framework avoids the primary disadvantage of using reflection
for this purpose, namely the loss of compile-time checking.

Can someone please provide an example that demonstrates how this mechanism enables classes in one package to access package-private methods in a different package?