ValueSource which resolves expressions against the environment variables
available from the underlying operating system (and possibly, the shell environment
that created the present Java process).
ValueSource implementation which simply wraps another value source,
and trims any of a set of possible expression prefixes before delegating the
modified expression to be resolved by the real value source.
ValueSource implementation that wraps a Properties instance,
and does a simple lookup of the entire expression string as the parameter for
Properties.getProperty(String), returning the result as the resolved
value.
ValueSourcenow.