code: def get_contents_dir(node):
      
      contents = []
      for n in sorted(node.children(), key=lambda t: t.name):
          contents.append('%s %s\n' % (n.get_csig(), n.name))
      return ''.join(contents)
docs: Return content signatures and names of all our children
      separated by new-lines. Ensure that the nodes are sorted.