Execute an action before visiting children of t. Return t or
a rewritten t. It is up to the visitor to decide what to do
with the return value. Children of returned value will be
visited if using TreeVisitor.visit().
post
java.lang.Object post(java.lang.Object t)
Execute an action after visiting children of t. Return t or
a rewritten t. It is up to the visitor to decide what to do
with the return value.