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 );
digester.addCallParam( "root/property", 0, "name" );
digester.addCallParam( "root/property", 1, "value" );
digester.addObjectCreate( "root/bean", SimpleTestBean.class );