// Fork the output: one copy goes to a SequenceOutputter which remembers the contents for
// use next time the variable is referenced; another copy goes to the current output destination.
SequenceOutputter seq = controller.allocateSequenceOutputter(20);
seq.setPipelineConfiguration(controller.makePipelineConfiguration());
seq.open();
TeeOutputter tee = new TeeOutputter(context.getReceiver(), seq);
tee.setPipelineConfiguration(controller.makePipelineConfiguration());
c2.setTemporaryReceiver(tee);
expression.process(c2);
seq.close();