@Override
        public void onBlockField(final Token token)
        {
            if (groupPath.isEmpty())
            {
                topLevelBlockFields.add(token);
            }

            groupPathsByField.put(token, currentGroupPath());
        }
Encodes the state machine as a graphviz dot diagram.
@param sb the string builder to append to.
@param indent the indentation to use.
sbe-tool/src/main/java/uk/co/real_logic/sbe/generation/common/FieldPrecedenceModel.java