{
Digester digester = new Digester();
MultiVariableExpander expander = new MultiVariableExpander();
expander.addSource( "$", mutableSource );
digester.setSubstitutor( new VariableSubstitutor( expander ) );
int useRootObj = -1;
Class<?>[] callerArgTypes = new Class[] { String.class, String.class };
CallMethodRule caller = new CallMethodRule( useRootObj, "addProperty", callerArgTypes.length, callerArgTypes );
digester.addRule( "root/property", caller );