Allows to use standard XML entities to include XML snippets into an
application context definition, for example to split a large XML file
into various modules. The include paths can be relative to the
application context's resource base as usual, instead of relative
to the JVM working directory (the XML parser's default).
Note: In addition to relative paths, every URL that specifies a
file in the current system root, i.e. the JVM working directory,
will be interpreted relative to the application context too.