code: public CompositeGeneratorNode indent(final CompositeGeneratorNode parent, final String indentString) {
      final IndentNode indent = new IndentNode(indentString);
      List<IGeneratorNode> _children = parent.getChildren();
      _children.add(indent);
      return indent;
    }
docs: Appends the indentation string at the current position of the parent and adds a new composite node, indicating the same indentation for
  subsequent lines.
  
  @return an indentation node, using the given indentString, appended as a child on the given parent