code: protected String getSpacer() {
          final StringBuilder output = new StringBuilder();
          final int indentationSize = parent != null ? getColumn() : 0;
          for (int i = 1; i < indentationSize; i++) {
              output.append(SPACER);
          }
          return output.toString();
      }
docs: Gets the spacer string to append before nodes in their toString methods.
  
  @return A string containing the amount of space to use for the node.