Given that much of the teaching material uses the
propagation pattern notation with wrappers and not the visitor notation
which is much closer to ordinary object-oriented programming,
you need to see several Demeter/Java examples to become
familiar with the traversal/visitor design notation of Demeter/Java.

The examples are in:
http://www.ccs.neu.edu/research/demeter/sources/DemeterJava/examples

Look at
j-selectively-explore/
to find out how you can selectively explore your objects.
This will help you understand the parsing process since you can
now "look" at the constructed objects.